AS2.4
Orals: Thu, 27 Apr | Room F2
By continuously monitoring greenhouse gas emissions from densely populated urban areas, we can independently assess and monitor emission reduction efforts at a policy-relevant scale. The EU-funded project PAUL (Pilot Application in Urban Landscapes - Towards integrated city observatories for greenhouse gases) develops, evaluates, and refines innovative greenhouse gas monitoring technologies including observational strategies for urban areas that enhance the capabilities of the Integrated Carbon Observation System at urban scales (ICOS Cities). In 2022, three pilot observatories have been set up to test, refine and optimize approaches for monitoring emissions from a metropolitan area (Paris, France), a large isolated city (Munich, Germany) and a mid-size city (Zurich, Switzerland). The three observatories have been developed in a co-design approach and integrated different observational technologies in support of inverse and inventory modelling. The pilot observatories focus on carbon dioxide (CO2) emitted from fossil-fuel sources.
The three observatories operate for a pilot phase of two years and collect comparative data across cities with a multitude of instrument networks that serve three main goals: (1) to assess the input for inverse models of CO2 at city-scale and attribute inferred CO2 emissions to sub-city scale and emission sectors; (2) to refine spatial, temporal, and sectoral attribution of emissions in emission inventories and parametrize process models that separate urban fossil-fuel and biogenic fluxes; and (3) as independent validation datasets to evaluate estimated emission products.
In all three cities, CO2 concentrations and selected co-emitted species are continuously sampled on tall towers, on top of high buildings and/or at street level. In the Paris metropolitan area, 10 tall tower sites and 30 roof-top sites continuously measure high-precision CO2 and co-emitted species in the boundary layer upwind, over and downwind of the city. The Munich and Zurich observatories feature a combination of roof-top and street-level sensor networks placed closer to sources and sinks, with a stronger signal strength that is more forgiving in terms of the sensitivity, hence allowing the deployment of mid- and low-cost sensors. In Paris and Munich, additionally, total column observations of CO2 are performed upwind, over and downwind of the main urban emission sources using concurrent ground-based FTIR spectrometers. Three new tall-tower eddy-covariance (EC) systems have been established in central Paris, Munich and Zurich. The EC-towers provide total CO2 fluxes for defined sub-areas of each city and their characteristic diurnal, weekly and seasonal cycles. Further, the three EC-towers provide sector-specific emission ratios and fossil-fuel CO2 fluxes based on differences of measured CO2-fluxes, six co-emitted species and radiocarbon fluxes. Finally, all cities have observational systems in place that monitor biogenic fluxes, vegetation dynamics and meteorological conditions, including lidars for wind and mixed layer determination for an improved quantitative description of atmospheric transport and vertical mixing.
We highlight design considerations for the three observatories and exemplarily show how multi-scale systems can efficiently complement and constrain fossil-fuel emissions in urban areas. Knowledge and experience from these observations will feed into the establishment of guidelines for operational greenhouse gas monitoring systems in European cities on their way to climate neutrality.
How to cite: Christen, A., Emmenegger, L., Hammer, S., Kutsch, W., D’Onofrio, C., Chen, J., Eritt, M., Haeffelin, M., Järvi, L., Kljun, N., Lauvaux, T., Loubet, B., Mauder, M., Mensah, A. A., Papale, D., Rivier, L., Stagakis, S., and Vermeulen, A. and the ICOS Cities Team: ICOS pilot observatories to monitor greenhouse gas emissions from three different-size European cities, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9884, https://doi.org/10.5194/egusphere-egu23-9884, 2023.
As cities are taking actions to reduce and offset part of their anthropogenic carbon dioxide (CO2) emissions, urban vegetation has become vitally important in pursuing carbon neutrality and climate mitigation. Its effectiveness in carbon sequestration, however, has large uncertainties due to the complex urban environment comprising both natural and artificial elements. By considering seven interacting land surface covers (buildings, pavement, evergreen trees, deciduous trees, grass, soil and water) within each model grid, the Surface Urban Energy and Water balance Scheme (SUEWS) is an urban land surface model that can simulate energy, water and CO2 exchanges in cities. For SUEWS to simulate the CO2 fluxes in urban green spaces, it requires information of maximum photosynthesis and surface conductance of specific urban vegetation as well as the response of surface conductance to environmental conditions. To derive these parameters, it is necessary to utilize on-site measurements conducted over urban green spaces for an accurate description of the surface processes and variables.
To our knowledge, only the mixed vegetation type and street trees in Helsinki have been parameterized in SUEWS so far. In order to extend the flexibility and usability of SUEWS modelling across different cities and for specific urban vegetation, this research aims to (1) derive surface conductance and photosynthesis parameters from eddy covariance and chamber measurements conducted over several urban sites corresponding to different urban vegetation types, such as non-irrigated lawn, turf grass, park trees, urban fields, green roof and urban forests (evergreen and mixed-leaf); and (2) evaluate the impact of selected surface conductance and photosynthesis parameters on SUEWS model performance in two mid-latitude cities: Swindon, UK and Minneapolis-Saint Paul, USA.
The surface conductance and photosynthesis parameters for specific urban vegetation are derived by fitting measurements to an empirical canopy-level photosynthesis model where the effect of the local conditions (i.e. meteorology and ecology) is considered. Using the bootstrapping method to randomly select seven-eighths of the available measurements for 100 times, the fitted maximum photosynthesis rates range from 5.27 μmol m-2 s-1 over an non-irrigated lawn to 10.72 μmol m-2 s-1 over an evergreen forest with the dependencies on the local environmental response functions such as air temperature, incoming shortwave radiation, specific humidity deficit and soil moisture deficit. As a following step, the choice of model parameters in SUEWS simulations will be examined in the two cities along with on-site measurements.
This research improves SUEWS simulations over urban areas by deriving new surface conductance and photosynthesis parameters specific to different urban vegetation types and provides a more accurate quantification of their biogenic CO2 flux in a complex urban environment. The results also provide a better understanding on the carbon sequestration potential of urban vegetation, which will be useful in planning urban green spaces to maximize natural carbon sinks and in setting climate mitigation strategies.
How to cite: Lee, H. S., Havu, M., Karvonen, A., Ahongshangbam, J., Soininen, J., Ward, H. C., McFadden, J. P., Lohila, A., Weber, S., and Järvi, L.: Parameterizing surface conductance of different urban vegetation types for the urban land surface model SUEWS with evaluation in two mid-latitude cities, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10032, https://doi.org/10.5194/egusphere-egu23-10032, 2023.
Understanding how cities impact the atmospheric boundary layer is crucial for many processes such as air-pollution dispersion and concentrations, and is therefore important as part of weather and climate modelling. To improve modelling of those dynamic processes observation are critical as they inform development and evaluation of models, and enhance delivery of services to citizens and the management of urban infrastructure, which is vulnerable to different strengths of heat and pollutant exposure.
During a year-long field campaign from Autumn 2021 to Autumn 2022 a comprehensive set of ground-based remote sensing observations were gathered in Berlin, Germany. These allow us to explore the impact of a large city on the regional atmospheric boundary layer. The campaign, undertaken within the European Research Council funded urbisphere project, involved a grid-like network of instruments in the densely built-up city centre, with ground-based remote sensing (e.g. automatic lidars and ceilometers ALC, Doppler-wind lidars) for mixed/mixing layer height (MLH) detection. Additional instruments were located along two perpendicular rural-urban-rural transects, with existing instruments in the city and surrounding region complementing the network. During Intensive Observation Periods (IOP) in spring and summer 2022 radiosonde releases within and outside the city during selected days allow air temperature, humidity and wind-distribution profiles in the atmospheric boundary layer to be investigated.
This contribution showcases how an urban environment modifies the dynamics and convective cloud properties under varying regional-scale weather conditions. We focus on case studies for different synoptic conditions to show the extent of impact of a large city on the MLH within and beyond the urban area, including urban-rural contrasts, upwind-downwind effects, and intra-urban variability of MLH.
How to cite: Fenner, D., Christen, A., Chrysoulakis, N., Grimmond, S., Van Hove, M., Kotthaus, S., Meier, F., Morrison, W., and Zeeman, M.: Impact of a large isolated city on the mixed layer height during different weather conditions, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11585, https://doi.org/10.5194/egusphere-egu23-11585, 2023.
In this study, geostationary satellite observations are used to develop and validate two high-resolution cloud-masking approaches for the region of Paris to show and improve applicability for analyses of urban effects on clouds.
Firstly, the Local Empirical Cloud Detection Approach (LECDA) uses an optimised threshold to separate the distribution of visible reflectances into cloudy and clear sky for each individual pixel accounting for its locally specific brightness. Secondly, the Regional Empirical Cloud Detection Approach (RECDA) uses visible reflectance thresholds that are independent of surface reflection at the observed location.
Results show that
- A decrease of cloud cover during typical fog or low-stratus conditions over the urban area of Paris for the month of November is likely a result of urban effects on cloud dissipation.
- The regional approach, RECDA, is a more appropriate choice for the high-resolution satellite-based analysis of cloud cover modifications over different surface types than LECDA with regional biases of ±5 %.
This approach can provide comprehensive insights into spatiotemporal patterns of land-surface-driven modification of cloud occurrence and locally induced cloud processes, such as the diurnal variation of the occurrence of fog holes and cloud enhancements attributed to the impact of the urban heat island. Further, it is potentially transferable to other regions and temporal scales for analysing long-term natural and anthropogenic impacts of land cover changes on clouds.
How to cite: Fuchs, J., Andersen, H., Cermak, J., Pauli, E., and Roebeling, R.: High-resolution satellite-based cloud detection for the analysis of land surface effects on boundary layer clouds, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6854, https://doi.org/10.5194/egusphere-egu23-6854, 2023.
The near-surface humidity is a crucial variable in many atmospheric processes, mostly in those related to development of clouds and rain. The humidity at the height of a few tens of meters above surface is highly influenced by the surface characteristics. In many cases the land-cover (LC) is responsible for the spatial variation of the surface humidity field, therefore, it is a major factor in determining the conditions for rainfall. Cities are one of the primary LCs which have a substantial impact on the humidity field. Large urban areas are expanding, causing a significant change in the near-surface humidity field. Measuring the near-surface humidity in high resolution, where most of the humidity’s sinks and sources are, is challenging with the common tools available today. Current measurement tools do not satisfactorily assess the cities’ effects on the humidity field. A new approach for measuring the humidity, based on the cellular network, provides high resolution information on the near-surface humidity. Therefore, we can examine the land-cover effect on the humidity in the low atmosphere in fine scale. In this study, the humidity field around Tel Aviv was retrieved from the cellular network during the summer of 2017. The results show a well-noticed impact of the city and other LC types on the humidity field over the Tel Aviv metropolitan area. The method presented here can offer an improved description of the humidity field at the city-canopy level and therefore provide a better assessment of the urban/LC effects on the environment, atmospheric modeling, and particularly on clouds/rain development.
How to cite: Rubin, Y., Sohn, S., and Alpert, P.: Urban moisture based on commercial microwave links (CML) data and relation to land-cover – case of Tel- Aviv metropolitan area , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4355, https://doi.org/10.5194/egusphere-egu23-4355, 2023.
Kolkata, one of the oldest and largest urban centres in Asia echoes all the major characteristics of cities from developing countries experiencing rapid urbanization and unplanned development. This study focuses on understanding the impact of intra-urban variations within a morphologically complex metropolis and its capability to modify the enveloping atmospheric conditions at the meso to micro-scale. The Weather Research and Forecasting (WRF) model was configured using a 3-tier nested domain to conduct high-resolution simulations incorporating improved land surface and urban parameterization and appropriate physical parameterization. Local Climate Zone (LCZ) map representing the land use land cover (LULC) was prepared for the innermost domain covering the city and surroundings using Planet-Scope datasets for 2019, adopting Artificial Neural Network (ANN) approach and validated using ground information. This was then integrated into the model with redefined values of specific urban parameters for a better representation of the city’s morphology. It was observed that LCZ-2 (Compact Mid-rise) and LCZ-3 (Compact Low-rise) cover almost the entire core city and around 70 % of the total built-up extent of the study area, which also consists of LCZ-5 (Open Mid-Rise) and LCZ-6 (Open Low-Rise) regions. Thus, the model was calibrated according to the surface and atmospheric conditions of the region and its performance was evaluated in comparison with ground observations. Simulations were conducted at hourly intervals for a 10-day period (August 2019) during the peak summers coinciding with the south-west monsoon period receiving heavy rain spells, to analyse the impact of heterogenous urban form on the micro-climatic variations within the city as well as its surroundings. The modelled results obtained for 2m air temperature (Tair), surface temperature (Tskin), 10m Wind Speed (WS) and Rainfall (RF) indicated a significant influence of the different LCZ classes and their spatial variations over the city. The average daytime Tair and Tskin values in the LCZ-2 is about 1℃ and 1.5℃ higher than LCZ-3, which is again 0.7℃ and 1.5℃ higher compared to the other urban LULC classes where the internal variation is relatively less. Further, the average temperature differences between the compact and open built-up structures increase significantly during night (2℃ – 3.5℃), further increasing when compared to the peri-urban (around 5℃). The inter-urban heterogeneity however, has a reverse effect on the average WS even during the typical monsoon period, with lowest speed observed in the compact core (2ms-1 – 5ms-1) due to highest surface drag (d), increasing (3ms-1 – 7ms-1) along LCZ-5 and LCZ-6 with reduction in d; which further increases substantially in the peri-urban areas (10ms-1 – 15ms-1) with lowest value of d. The variations in total RF received from the complex towards peripheral urban also depicts a similar pattern, as average RF intensity is the lowest within LCZ-2 and LCZ-3 (7mm/hr – 15 mm/hr), moderate in LCZ-5 and LCZ-6 (10mm/hr – 20mm/hr) and highest along the peri-urban areas (15mm/hr – 35 mm/hr). Thus, urban structural and morphological complexity can have a substantial effect on the local-scale climatic variations even along small horizontal distances within a city.
How to cite: Bhattacharjee, S. and Bharti, R.: Intra-urban morphological heterogeneity and its impact on the micro-climatic variations in the Kolkata Metropolitan region of India, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-16058, https://doi.org/10.5194/egusphere-egu23-16058, 2023.
Understanding the role of surface heterogeneity of surface fluxes in the development of convection is a critical topic in land-atmosphere interactions. This is especially relevant in the context of Earth System Models (ESMs), where simulated sub-grid surface heterogeneity over the land surface is mostly ignored by the overlying modeled atmosphere. Indeed, previous studies using Large Eddy Simulation (LES) have shown that heterogeneities in the surface field below ESM spatial resolution (~100 km) can cause appreciable secondary circulations and, at times, a significant increase in convective cloud development. These large scale changes initiated by small scale heterogeneity have yet to be adequately parameterized in ESMs. To address this particular weakness, this presentation presents a parameterization scheme for a near surface density driven circulation between two lower atmosphere columns with variable surface heating for use within ESMs.
The secondary circulation parameterization is fit to data from 184 LES runs over 92 days, one run each day with a homogeneous surface and one run each day with a heterogeneous surface derived from land surface model output, over a 100 km square domain centered around the ARM site in the US Southern Great Plains (SGP) in Oklahoma. It is then tested over those 92 simulation days at the SGP site, as well as shallow convective days over four heterogeneous sites where differential heating is common: Wisconsin (lake-land), Florida (ocean-land), Missouri (urban-rural) and Appalachia (elevation).
To test the circulation scheme, we use standalone columns of Cloud Layers Unified by Binormals (CLUBB) a boundary layer, cloud and shallow convection scheme used in multiple modern ESMs. CLUBB is run for three cases on each simulation day at each site: 1) as a single homogeneous column model over the domain, 2) as two separate columns over high and low sensible heat portions of the domain, and 3) following 2) with the addition of the circulation parameterization scheme. The homogeneous CLUBB simulations and those with secondary circulations are compared to evaluate the impact of the secondary circulation on cloud development, turbulent kinetic energy, and profiles of the means and variances of heat and moisture. Results over the SGP site show that the parameterized circulation yields similar changes in cloud development and profiles of heat and moisture to LES.
How to cite: Waterman, T., Bragg, A., Hay-Chapman, F., Dirmeyer, P., Fowler, M., and Chaney, N.: Parameterizing the Large Scale Impact of Land Surface Heterogeneity Induced Circulations on Convective Cloud Development, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10938, https://doi.org/10.5194/egusphere-egu23-10938, 2023.
Land-atmosphere energy and moisture exchange can strongly influence local and regional climate changes. However, high uncertainties exist in the representation of land-atmosphere interactions in numerical models and the coupling strength between land and atmosphere is largely overestimated, in which the determination of surface exchange coefficient is one of the main problems. Here, we show the improvements from a dynamic vegetation-type-dependent exchange scheme in the offline Noah land surface model with multi-parameterization options and the Weather Research and Forecasting model when applied to China. Compared to the default schemes, the dynamic exchange scheme significantly reduces land-atmosphere coupling strength overestimations, and comparisons to flux tower observations reveal its capability to better match observed surface energy and water variations. In particular, the above remarkable improvements produced by the dynamic exchange scheme primarily occur in areas covered with short vegetation. The improved version benefits from the treatment of the roughness length for heat. Further, land-surface processes play significant roles in cloud formation and precipitation generation by affecting local planetary boundary layer profiles. The dynamical exchange scheme could narrow the positive discrepancies in the simulated precipitation. Using 3-km-resolution convection-permitting models for three heavy precipitation cases, the dynamic coupling simulations could achieve the closest agreement with the field observations, especially the intensity and location of the heaviest rainfall during the precipitation process. Overall, our findings highlight the applicability of the dynamic scheme as a better physical alternative to the current treatment of surface exchange processes in atmosphere coupling models and could help achieve more accurate simulations.
How to cite: Zhang, X., Chen, L., and Ma, Z.: Improvement of surface exchange coefficient parameterization and its application to regional numerical simulation, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3423, https://doi.org/10.5194/egusphere-egu23-3423, 2023.
Orals: Fri, 28 Apr | Room F2
Surface solar irradiance varies on scales down to seconds or meters due to clouds. This highly variable nature of irradiance is not resolved by atmospheric models, yet heterogeneity in surface irradiance impacts the overlying cloud field. The inability to resolve irradiance variability, aside from insufficient model resolution, is explained by our limited understanding of cloud-driven solar irradiance variability at short spatiotemporal scales and the lack of high resolution spatial observational data. Cloud resolving models utilizing ray tracing techniques are a useful research tool, but ultimately require validation against observations.
In 2021, we gathered new observational data with a network of radiometers, specifically designed to gather data on cloud-driven surface patterns of irradiance. I will present results on various kinds of surface patterns in relation to cloud type and atmospheric conditions, based on these observations. Our radiometers sample surface solar irradiance at 10 Hz for 18 wavelengths, which we deployed in different setups in the FESSTVaL (Germany) and LIAISE (Spain) field campaigns. Our results highlight the complexity and wide range of regimes in spatiotemporal irradiance variability, but also provide insights into its driving mechanisms. These insights help guide the development of improved radiative transfer calculations, in order to move towards models that can accurately resolve irradiance variability in an operational setting.
How to cite: Mol, W., Heusinkveld, B., Hartogensis, O., and van Heerwaarden, C.: Cloud-driven patterns of surface solar irradiance as seen by a spatial network of radiometers, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-5762, https://doi.org/10.5194/egusphere-egu23-5762, 2023.
Irrigation is still widely neglected in land surface models which are used for numerical weather prediction. However, with the general improvement of coupled surface-atmosphere models and the evolution towards kilometer or hectometer grids, this omission is beginning to be reconsidered. Better understanding the links between the strong surface heterogeneity and local meteorology is one of the objectives of the LIAISE (Land surface Interactions with the Atmosphere In Semi-Arid Environment) project. The work presented here focuses on two clear and warm days of the special observation period of the LIAISE campaign that took place during the summer of 2021 in northeastern Spain. The coupled surface-atmosphere model Surfex-MesoNH is used to model two days of interest with and without an irrigation parameterization. The model outputs are then compared to multiple surface-based and airborne observational data. A clear improvement is provided by the irrigation representation. In particular, the modeled sensible and latent heat fluxes are reconciled with the observations, the temperature biases at 2m are corrected up to 5°C, and the specific humidity is increased by about 50% around noon near the surface. It is also shown that irrigation leads to changes in the structure and height of the atmospheric boundary layer. A breeze-like, non-classical mesoscale circulation induced by the surface contrasts between the irrigated area and the surrounding semi-arid area is highlighted.
How to cite: Lunel, T., Boone, A., and Le Moigne, P.: Influence of irrigation on land-surface interactions and the atmospheric boundary layer in a semi-arid region – Results from the LIAISE campaign, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-2253, https://doi.org/10.5194/egusphere-egu23-2253, 2023.
Turbulence is essential for land atmosphere interactions; however, it is difficult to quantify because of its statistical nature. Typically, turbulence is determined using time series data, on which Taylor’s hypothesis is applied to obtain turbulent data over a length scale. Taylor’s frozen turbulence hypothesis is an assumption in the core of turbulence research, however currently turbulence measurements are limited to either time series (e.g., sonic anemometers) or integrated spatial measurements (e.g., scintillometers). Therefore, the spatiotemporal nature of turbulence cannot be independently assessed. In this study we use fiber-optic distributed sensing (FODS) to measure turbulence over both time and space.
The turbulence parameter used is the structure parameter of temperature, CT2, which quantifies the intensity of temperature fluctuations over a certain scale. The structure parameter can be determined using temperature series directly, using its definition. Alternatively, the inertial range of the turbulent temperature spectrum can be used to obtain structure parameter through the Kolmogorov -5/3 power law.
A FODS experiment was conducted in the LIAISE (Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment) field campaign during 15-30 July 2021 in the north-east of Spain. A set-up was installed with a horizontal extent of 70 m, measuring at four heights between 0.40 m and 2.05 m. A thin 0.5 mm cable was used in an effort to obtain the fastest possible time response. Measurements were made at 1 Hz and 12.7 cm resolution, however the actual sampling frequency appeared to be 0.15 Hz in the temperature spectrum, likely because of the long response time of the cable.
Despite the limited 0.15 Hz sampling rate it was possible to obtain turbulence information through the use of the structure parameter of temperature. This parameter indicates the intensity of temperature fluctuations and was calculated over time, as is conventional. In a novel approach, it was also calculated over space. The spatial structure parameter obtained through the definition method was found to have the best correlation with a sonic anemometer reference, with a correlation coefficient of 0.88.
The temporal structure parameter lacks the structure that is shown in the spatial method, which is likely due to the use of 30-min averaged data for horizontal wind speed from the sonic anemometer or to Taylor's frozen turbulence hypothesis not being a suitable assumption within the dimensions of this research. Determining structure parameters through the turbulent spectrum was successful for limited data points for the time seriess and is currently inconclusive for the spatial series. This work provides a first step towards using FODS in capturing turbulent information along spatial temperature series.
How to cite: Vis, G., Hartogensis, O., ten Veldhuis, M.-C., and Coenders, M.: Can fiber-optic distributed sensing be used to resolve temperature turbulence values over time and space?, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15992, https://doi.org/10.5194/egusphere-egu23-15992, 2023.
Representing the diurnal variability of state meteorological variables, including carbon dioxide, is still an open challenge as shown by the large discrepancies with observations and weather and climate models. These discrepancies translate into different diurnal exchanges of heat, water and carbon dioxide between the canopy and atmosphere. These sub-diurnal differences can propagate to larger temporal and spatial scales.
With a systematic approach, we investigate the diurnal gas exchange of both water and carbon dioxide for an irrigated crop. Our investigation is based on a comprehensive observational dataset that ranges from scales covering from the leaf level to the canopy level to the atmospheric boundary layer gathered at the LIAISE campaign. This campaign took place over two weeks in summer of 2021 in a region of the Ebro basin located in Catalonia, Spain. We focus specially on one of the “supersites” of the campaign: La Cendrosa, which is an irrigated alfalfa field surrounded by a very dry region.
Our observational approach is bottom-up in which we first analyze the leaf, second the canopy and third the interactions with the atmosphere at a local field scale. Among the observations, we analyzed leaf gas exchange measurements, turbulent surface fluxes and vertical profiles of driving environmental variables such as radiation, wind, temperature, and specific humidity. To support the observational analysis, we use a land-atmospheric interactive model (CLASS model). This model allows the representation at each of the three levels mentioned: (1) leaf, (2) canopy and (3) field.
Our observations show an asymmetry in the diurnal variability of the stomatal conductance, which indicates a larger opening of the stomata during the morning than during the afternoon. To attribute processes to the causality in the stomatal opening, we derive new expressions of the tendency of the stomatal aperture as a function of the mean meteorological drivers including radiation, temperature, atmospheric CO2 concentration, and water vapor deficit. The asymmetry is only simulated by models once specific characteristics of the crop are considered. It is also observed that dynamics at the leaf level such as a closure of the stomata during the midday can cause a dip in the evapotranspiration and enhance the sensible heat flux. Our results open the debate on the circumstances under which it is important to constrain the leaf gas exchange.
How to cite: González Armas, R., Vilà-Guerau de Arellano, J., de Boer, H., Hartogensis, O., Mangan, M. R., and Gibert, F.: On the impact of leaf-level processes on the water and carbon canopy-turbulent fluxes, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10397, https://doi.org/10.5194/egusphere-egu23-10397, 2023.
This study employed fiber-optic distributed temperature and wind speed data in the forest environment, together with a scalar gas sampling network and eddy covariance measurements, to address questions concerning scalar gas mixing and transport under weak-wind conditions. We also investigate advection term variability using distributed wind speed to determine how it influences the CO2 budget in the subcanopy. Preliminary results demonstrate that employing friction velocity and bulk shear filtering to define weak and strong wind conditions separates the vertical temperature and scalar gas profiles but not the horizontal. Furthermore, the biggest scalar gas spatial variations occur at night, when wind direction and TKE magnitudes are most influential. The inlets positioned in a route related to a clearing cut show the most variability among the scalar gas inlets, illustrating the influence of subcanopy architecture on mixing and transport along the subcanopy.
How to cite: Abdoli, M. and Thomas, C.: Investigating transfer and mixing in the sub-canopy using fiber-optic driven distributed temperature and wind speed and scalar gas sampling network, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13079, https://doi.org/10.5194/egusphere-egu23-13079, 2023.
Isoprene and monoterpene emissions from the terrestrial biosphere play a significant role in major atmospheric processes. Such emissions account for 90% of the total volatile organic compound (VOC) emissions and exert a significant influence on the atmosphere's oxidation capacity, aerosol formation and in turn, clouds and climate. Emissions depend on the vegetation response to atmospheric conditions (primarily temperature and light), as well as other stresses e.g. from droughts and herbivory. The El Niño-Southern Oscillation (ENSO) is a natural cycle, arising from sea surface temperature (SST) anomalies in the tropical Pacific, which perturbs the natural seasonality of weather systems on both global and regional scales. Several studies evaluated the sensitivity of BVOC fluxes during ENSO events using transient simulations. While these studies employ realistic scenarios, it is difficult to assess the individual impact of ENSO given multiple forcing on the climate system (e.g. from CO2, aerosol, etc.). In this work, simulations from a global atmospheric chemistry-climate model with enabled interactive vegetation are used to assess changes in vegetation (net primary production (NPP) and leaf area index (LAI)), meteorology (surface temperature, surface radiation, and precipitation), and consequently, isoprene and monoterpene emission changes attributed to ENSO. Global isoprene emissions could increase by 4% during strong El Niño events with substantial regional changes e.g. + 20% over Amazonia. Changes in isoprene and monoterpene emissions are evaluated in response to meteorological and vegetational variability.
How to cite: Vella, R., Pozzer, A., Lelieveld, J., Forrest, M., and Tost, H.: Isoprene and monoterpene emission response to the El Niño-Southern Oscillation, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-1565, https://doi.org/10.5194/egusphere-egu23-1565, 2023.
Biogenic volatile organic compounds (BVOCs) are emitted into the atmosphere by plants and other living organisms and play a significant role in various plant functions, such as growth, reproduction, and defense. BVOCs are also an essential part of many chemical reactions in the atmosphere and contribute to the formation of ozone and secondary organic aerosols and affect the radiation balance.
Investigating the atmospheric vertical profile concentrations of BVOCs has become an important focus for understanding these processes. There are various methods that can be used to study the atmospheric vertical profile, including towers, balloons, aircraft, and unmanned aerial vehicles (UAVs). Among these methods, UAVs offer greater flexibility for local air sampling by hovering over a target area and can reach altitudes of up to 1000m, making them ideal for permanent BVOCs monitoring that requires repeated measurements in a specific spatial and temporal domain. However, the source contribution area of the obtained BVOCs concentrations is often not identified, potentially leading to inaccurate conclusions about the exchange between the surface, vegetation, and atmosphere above the target area.
In this study, the vertical profile of BVOCs concentrations was obtained at SMEAR Estonia (Station for Measuring Ecosystem Atmosphere Relations) to analyze the composition and distribution of these compounds in the near-surface layer. The vertical samples were collected in 2020-2021 using a commercially available pump equipped with cartridges filled with adsorbents and mounted on a UAV. The UAV was used to collect samples from heights between 0 m and 90 m.
To address the issue of space-time representativeness related to the source signal, a footprint analysis was conducted. Micrometeorological data for four target areas were obtained from three SMEAR Estonia flux towers. The Flux Footprint Prediction model (Kljun et al., 2015) was used for the footprint calculation. We determined temporal and spatial changes in roughness length (z0) and zero-displacement height (zd) for each day when BVOCs measurements were carried out using meteorological and geospatial data on land cover types and corresponding canopy heights. Due to the presence of surface heterogeneity, z0 and zd varied significantly for each wind sector. Therefore, we ran the spin-up of the FFP model with updated input parameters at each step. For the measurement results interpretation, we also evaluated the representativeness of the obtained footprints over the target areas in the space-time domain and analysed the land cover composition and vegetation characteristics.
In this work, we show how the source contribution area of BVOCs concentrations can vary in size and shape depending on atmospheric conditions, and spatial and temporal variation and thus have an effect on the obtained species composition of BVOCs. Based on the presented findings we discuss the potential implementation of this approach for similar research and its future development.
How to cite: Krasnov, D., Zolotarjova, V., Krasnova, A., Kask, K., Niinemets, Ü., and Noe, S.: An implementation of the advanced footprint analysis for UAV-based BVOC measurements, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11370, https://doi.org/10.5194/egusphere-egu23-11370, 2023.
Methane (CH4) is a strong greenhouse gas that is produced in anoxic soil conditions. Wetlands are the largest natural source of CH4 globally because their anoxic soils provide suitable habitats for CH4-producing Archaea. Both global and regional wetland CH4 budgets remain unconstrained due to large uncertainties in wetland extent and high spatio-temporal variability in CH4 dynamics that are in part driven by wetland spatial heterogeneity. High wetland spatial heterogeneity often results from the variability in microtopography, soil hydrological and chemical properties, and vegetation and microbial composition. Intertwined together, the different abiotic and biotic variables further contribute to the ratio between CH4 production, consumption and transport processes in wetland soil, resulting in either net CH4 emission or uptake. However, the contribution of different abiotic and biotic factors to CH4 flux variability in wetlands remains unclear, increasing uncertainties in up-scaling CH4 emissions from plot to ecosystem and regional scales. Therefore, including well-defined spatial heterogeneity into wetland CH4 bottom-up estimates can help improve the regional and global CH4 budget calculations.
This study investigates the effect of spatial heterogeneity on observed CH4 emissions in ten different wetland sites with varying climatic conditions. Our approach will include up-scaling chamber measurements from different land cover classes to the level of the eddy covariance (EC) footprint. The compiled chamber datasets include both manual (n=5) and automatic (n=5) measurements that have been combined with EC measurements (FLUXNET-CH4 database) based on matching timestamps. First, the chamber observations will be compared to the corresponding EC measurements without accounting for spatial heterogeneity. Then, various remotely sensed environmental variables, such as leaf area index (LAI) and topographic wetness index (TWI), in high spatial resolution will be used to create land cover classes and combined with a modeled footprint to include spatial heterogeneity in the up-scaling of point-level measurements in all sites.
Preliminary results suggest that the chamber and EC observations differ significantly in magnitude between seasons and sites. In general, chamber observations had a larger range than EC, which we expected, given that chambers capture finer spatial heterogeneity than EC. However, no consistent trends emerged in the difference in magnitude between chamber and EC. We expect that the inclusion of spatial heterogeneity into the footprint model will decrease the differences between up-scaled chamber and EC observations for all sites. Notably, we expect that the inclusion of proxies for soil moisture, plant functional type (PFT) and aerenchyma will improve footprint-level comparisons to chamber-level data. We will present updated comparisons of EC and chamber data with and without inclusion of spatial heterogeneity. Altogether, this study will establish a workflow for combining wetland CH4 data from different measurement types (EC and chamber) and will allow global syntheses to use more of the available data to constrain CH4 budgets.
How to cite: Määttä, T. and Malhotra, A. and the FLUXNET-CH4 EC-chamber working group: Effects of spatial heterogeneity within the eddy covariance (EC) footprint on up-scaled methane fluxes across multiple wetland sites, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3338, https://doi.org/10.5194/egusphere-egu23-3338, 2023.
Non-rainfall water can play a critical role in many ecosystems, but is understudied in most regions due to a lack of continuous, specialized measurements. One of the most commonly used techniques to quantify in situ ecosystem water fluxes is Eddy Covariance (EC). However, its use for the quantification of the two most famous non-rainfall water sources, dew and (radiation) fog, is limited because they often occur under humid conditions and nighttime stable stratification, making EC measurements particularly uncertain or non-valid.
Here we describe how a non-rainfall water input observed under dry conditions, namely water vapor adsorption by soil particles (VWA), can be monitored using existing eddy covariance datasets, giving insight into this little-studied soil water source. Unlike dew and radiation fog, atmospheric stability is not a prerequisite for WVA. Instead, WVA is driven by a highly negative soil matric potential inducing water vapor to condensate already at relative humidity < 100 %. Therefore, EC measurements may be more suitable to detect and quantify this flux than for dew and fog.
In this study, we test EC measurements for inferring WVA by comparing them to observations from large-weighing lysimeters, where the latter can be considered as a reference system for the measurement of WVA. Our aim is to explore the potential and limitations of the EC technique to detect and quantify WVA. We assess the quantitative and qualitative agreement between WVA estimated with the lysimeters and negative (downward) LE fluxes from EC. Our analysis uses four years of observations from a semi-arid tree-grass ecosystem and one year of a temperate agricultural ecosystem during the 2018 drought.
Our results show that during dry conditions the water vapor gradient between the relatively humid atmosphere and the dry soil pores leads to WVA in both ecosystems. We find a decent agreement between the timing of fluxes detected as WVA with lysimeters and with EC instruments, but the magnitudes (i.e. the amount of flux) differ. Furthermore, we aim to characterize the conditions under which negative LE fluxes from EC measurements can and should be interpreted as WVA. This way, our study expands the possibilities to investigate the relevance of WVA as a non-rainfall water source and, more generally, sheds light on a mostly overlooked aspect of land-atmosphere interaction during dry conditions in different ecosystems.
How to cite: Paulus, S. J., El-Madany, T. S., Orth, R., Hildebrandt, A., Reichstein, M., Nelson, J. A., Carrara, A., Moreno, G., Mauder, M., Groh, J., Lee, S.-C., and Migliavacca, M.: Interpretability of negative latent heat fluxes from Eddy Covariance measurements during dry conditions, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7666, https://doi.org/10.5194/egusphere-egu23-7666, 2023.
Most of the water input to the ecosystem comes from rainfall. However, depending on the local climatic conditions a considerable amount of water can also be produced by different fractions of non-rainfall water inputs (NRWIs), namely dew, hoarfrost, rime, fog, and the adsorption of water vapour in the soil. Such NRWIs are often neglected because they are typically small compared to rainfall on the daily scale. Nevertheless, these NRWIs provide our ecosystems with additional water, which is important for the survival of the fauna and flora in the ecosystem, especially during dry periods.
In the past different devices were used to determine some of these fractions, based on artificial surfaces (e.g., dew or fog collector). We will present a conceptual measurement set-up that allows us to determine each non-rainfall water (NRW) component for natural surfaces of agricultural ecosystems. The method is based on precise weighable lysimeter measurement to determine the incoming water fluxes of NRW. The partitioning between the NRW components will be done based on parallel observations on the surface and air temperature, humidity, rain gauge, and dust collector. Based on this conceptual system, we will compare the temporal development and occurrence of different NRW components for eight different agroecosystems under similar climatic conditions.
How to cite: Groh, J., Pütz, T., Beysens, D., Vereecken, H., and Amelung, W.: A conceptual system for identifying and distinguishing different non-rainfall water fractions in agroecosystems, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-5833, https://doi.org/10.5194/egusphere-egu23-5833, 2023.
The non-closed energy balance is still an unsolved problem of eddy covariance measurements: when the net radiation budget is compared with all the different energy exchange components measured at the flux station there is a general systematic imbalance, highlighting that one or more energy components are either underestimated or not measured. Different hypotheses have been stated and many analyses into potential causes have been performed in the past years, ranging from methodological problems (water vapour flux underestimation due to condensation or unaccounted spectral damping in the analyser tube, underestimation of the vertical wind speed component due to transducers shadowing in the sonic anemometers), to components not fully monitored (e.g. the heat stored in the vegetation) different sensor footprints and field of views, to large scale motions particularly relevant in heterogeneous and fragmented landscapes. All these aspects are important and probably the issue of the energy balance non-closure is due to a combination of all the factors.
The ICOS Ecosystem network consists of a set of eddy covariance stations equipped with high-level and quality standardized instrumentation, whose data are processed centrally. The availability of these data (freely accessible through the ICOS Carbon Portal) allows for a systematic analysis of the importance of the different measured energy components (soil heat flux and the soil storage above the soil heat flux plates, air mass storage of sensible and latent heat measured with sensors along vertical profiles) in relation to various data quality filtering steps applied (raw data screening, low turbulence conditions etc.). The results show that improving the measurement and the quality control of the energy components, leads to an average 10% increase of the energy balance closure. This is not yet sufficient to obtain a perfect closure of the balance and further investigation is needed but helps to identify the magnitude of the real imbalance to be explained. Analysis of data collected under different environments and conditions helps also to identify and better understand the main possible causes of the energy balance non-closure.
How to cite: Papale, D., Nicolini, G., Op de Beeck, M., Sabbatini, S., Galvagno, M., and Gielen, B. and the ICOS Ecosystem Stations PIs: How much additional improvements in measurements and data filtering can help to close the energy balance at eddy covariance stations, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9974, https://doi.org/10.5194/egusphere-egu23-9974, 2023.
Accurate quantification of evapotranspiration (ET) is crucial for understanding variability in the global water cycle, yet state-of-the-art estimates of ET derived from models and remote sensing products contain large uncertainties. Taking the advantage of extensive eddy covariance measurements and machine learning algorithms, ET can be upscaled from globally distributed in-situ observations by combining them with global meteorological and satellite data (e.g., FLUXCOM ensembles, Jung et al., 2019). However, eddy covariance measurements suffer from well-known energy balance non-closure problems, and those uncertainties are further propagated to the global ET estimates. Here, we first estimate the energy balance non-closure within dynamic sliding windows for flux tower site, then we compute correction factors for ET measurements following different hypothesis (that assign errors to latent and/or sensible heat fluxes) according to insights from large eddy simulation studies. Then energy balance closure corrected ET data are used in FLUXCOM to estimate global ET. The upscaled ET then is evaluated by comparison with water-balance-drived ET at the catchment level. This comparison helps to determine the most consistent correction of ET for different regions and conditions. By providing improved global ET estimates, water-related studies can be further facilitated, and model parameterizations can be further optimized to address the challenges posed by climate change on ecosystems and water resources.
How to cite: Zhang, W., Nelson, J. A., Miralles, D. G., Poyatos, R., Reichstein, M., and Jung, M.: Towards reducing uncertainties of global evapotranspiration due to the energy balance closure gap in flux tower data, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11031, https://doi.org/10.5194/egusphere-egu23-11031, 2023.
The eddy covariance (EC) method, nowadays the standard method for determining forest ecosystem-atmosphere turbulent exchange, faces a major threat in its application: the air masses below the canopy are regularly decoupled from the air masses above the canopy. Consequently, the EC measurements above the canopy like e.g. H2O and particularly CO2 fluxes can be biased due to missing signals from below-canopy processes. This decoupling is strongly site dependent and influenced by meteorological conditions, canopy properties and tower-surrounding topography. It can be verified and addressed by subsequent EC measurements below and above the canopy. Specifically, the correlation of σw below and above the canopy gives information about the coupling state as this correlation is linear during periods of full coupling.
The current study aims to address the decoupling issue on a global scale. For this purpose, approximately 30 forest sites from around the world will be analyzed in a standard way with regards to decoupling. The study sites cover manifold vegetation types and climate zones, all sites are equipped with concurrent below and above canopy EC measurements. Preliminary results highlight the dependence of decoupling on meteorological conditions, canopy properties and tower surrounding topography. Nevertheless, the final goal of this action is to derive global relations between these influence factors and decoupling which will be applicable in a general way on each forest site worldwide. Highest quality turbulent fluxes will be the outcome and the accuracy of EC derived forest water and carbon budgets will improve.
How to cite: Jocher, G.: Addressing forest canopy decoupling on a global scale, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4877, https://doi.org/10.5194/egusphere-egu23-4877, 2023.
Evapotranspiration (ET) from the land surface to the atmosphere consists of transpiration (T) from plants and evaporation (E) from soil and vegetated surfaces. These biological and physical component fluxes respond differently to changes in temperature, water availability and atmospheric composition. ET can be measured directly at the ecosystem scale with the eddy covariance (EC) method but similar measurements are not currently available for the component fluxes E and T. Concurrent EC measurements above and below forest canopies provide a promising approach to partition ET into T and E. However, our understanding of the performance of such measurements is still very limited. To address these challenges, we measured and partitioned ET with three concurrent EC towers (1 above & 2 below canopy) in a montane forest at Sagehen Creek in the Sierra Nevada, California from late June 2017 to September 2020. We observed a total forest ET of 606 mm yr-1 with 275 mm yr-1 measured in the understory and a tree transpiration of 331 mm yr-1. Below-canopy measurements replicated at two locations within the above-canopy footprint indicated only small spatial variability for understory ET near the creek at Sagehen. Interannual variability in ET above and below canopy was small during the water years 2018 to 2020, despite large variability in precipitation totals. Accordingly, vegetation water use was relatively stable across years and the P–ET water balance was mainly driven by variations in water supply. Partitioning the components of total forest ET at Sagehen with concurrent EC measurements showed that on average 67–74% originated from T (47% from trees and 20–27% from understory grasses), while 26–33% were from E (mostly from the understory). Our results demonstrate the strength of concurrent above- and below-canopy EC measurements for the partitioning of ET.
How to cite: Wolf, S., Paul-Limoges, E., Sayler, D., and Kirchner, J. W.: Evapotranspiration dynamics and partitioning from concurrent above and below canopy flux measurements in a Montane Sierra Nevada Forest, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12068, https://doi.org/10.5194/egusphere-egu23-12068, 2023.
Water vapor flux plays a crucial role in surface-atmosphere exchange processes as evapotranspiration regulates the energy balance of the surface. Moreover, it transfers water vapor into the atmosphere and, as a result, shapes the hydrological cycle. The eddy-covariance (EC) technique is the most commonly applied method to directly measure water vapor flux over a wide variety of surfaces. An EC arrangement consists of a 3D sonic anemometer and a gas analyzer. To derive surface fluxes, wind components and the gas concentration (e.g. water vapor) have to be recorded with high-frequency (at least at 10 Hz). In the case of open-path (sampling-free) EC systems, infrared (IR) gas analyzers are used dominantly, which are still quite large so that e.g. they cannot be easily mounted on drones. In contrast, small and light sonic anemometers are available for flux measurements.
In this study, we present the application of a sampling-free photoacoustic (PA) sensor for water vapor flux measurement employing the EC technique. The fast response PA sensor records the water vapor concentration through an open cylindrical chamber having an overall size of less than 1 dm3. On the one hand, a previous first test showed that the vertical covariance functions obtained by the PA cell follow closely to those resulting from an accepted IR sensor. On the other hand, the PA system showed some underestimation at higher frequencies based on the analysis of co-spectra.
To comprehensively test and evaluate the PA cell for flux measurements, a seven-week-long field measurement was performed over a plain grassland when a calibrated EC150 IR sensor (Campbell Sci.) was used as a reference gas analyzer. We analyze the accuracy of the PA system: (i) depending on the orientation of the cell or i.e. the wind direction, and (ii) for a broad range of meteorological conditions, such as different wind speeds and atmospheric stability. Furthermore, to overcome the high-frequency attenuation, we establish and apply empirical spectral transfer functions following the literature and standard EC postprocessing procedures. The characteristic response time of the PA sensor is also assessed.
How to cite: Torma, P., Weidinger, T., Juhász, V., Molnár, B., Horváth, L., Huszár, H., and Bozóki, Z.: Application of open photoacoustic cell in an eddy covariance system for water vapor flux measurement, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12898, https://doi.org/10.5194/egusphere-egu23-12898, 2023.
Monitoring of trace gas fluxes and greenhouse gas fluxes is key to understand the interaction between atmosphere, plants, and soil and therefore to improving our understanding of the climate system in general.
The complex flux systems require measurement of many different inert and reactive trace gases and greenhouse gases simultaneously to obtain a complete budget. This is especially the case in urban environments where both biogenic and anthropogenic sources and sinks play a role.
The eddy covariance (eddy flux) technique is often used to determine fluxes of the gases in question. Until recently, however, the monitoring was usually limited to only a few gases per measurement device making the technique complex and expensive but providing only a limited picture. MIRO Analytical has developed a novel multicompound gas analyzer that can monitor up to 10 air pollutants (CO, NO, NO2, O3, SO2 and NH3) and greenhouse gases (CO2, N2O, H2O and CH4) simultaneously with the high time resolution necessary for eddy-covariance flux measurements. The compact system combines several mid-infrared lasers (QCLs) providing outstanding precision, selectivity and accuracy for the gas measurements.
In our contribution we will introduce the measurement technique and will demonstrate application examples of this all-in-one atmospheric flux monitor. The system will be compared to alternative devices in parallel measurements and results of long-term observations and shorter campaigns will be presented.
How to cite: Hundt, M., Brunner, M., and Aseev, O.: Simultaneous eddy flux monitoring of 10 greenhouse gases and air pollutants with a single instrument, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7803, https://doi.org/10.5194/egusphere-egu23-7803, 2023.
Two micrometeorological methods that utilize high frequency sampling of air temperature were tested against eddy covariance (EC) sensible heat flux (H) measurements at three sites representing agricultural, agro-forestry and forestry systems. The two methods encompass conventional and newly proposed forms of the flux-variance (FV) and surface renewal (SR) schemes. In terms of measurement setup, the sites represent surface, roughness and roughness to surface transitional layers, respectively. After the selection of the most reliable approaches, regression analyses against EC showed that both methods can estimate H with slopes within ±10 % from unity, and coefficient of determination R2 >0.9 across all three sites. The best performance, of both FV and SR, was at the agricultural field, where the measurements were within the surface layer. The worst performance occurred in the tall, relatively heterogeneous forest, where the measurements were taken in the roughness sublayer, the depth of which (with its inherent uncertainty) needs to be taken into account in the calculations. In addition to the evaluation of the FV and SR forms, an alternative perspective relating ramp-like structures to the vertical temperature gradients in the surface boundary layer is introduced here. Ramp-like structures carry much of the heat flux and temperature variance, representing opportunities to constrain the coefficients of the two methods. As a corollary, we introduce a novel approach emerging from bridging FV and SR methods that combines information about the coherent structures with the overall variance to obtain heat fluxes in a turbulent atmosphere. The proposed approach yields reliable H estimates without the need for site-specific calibration and instrumentation other than a single fast thermocouple.
Acknowledgement: This study was conducted with support of SustES - Adaptation strategies for sustainable ecosystem services and food security under adverse environmental conditions (CZ.02.1.01/0.0/0.0/16_019/0000797) and USDA NIFA-AFRI Sustainable Bioenergy Program, 2011-67009-20089, Loblolly pine-switch grass intercropping for sustainable timber and biofuels production in the Southeastern United States. Funding for AmeriFlux core site US-NC4 (natural forested wetland) was provided by the USDA NIFA (Multi-agency A.5 Carbon Cycle Science Program) award 2014-67003-22068. Additional funding was provided by the DOE NICCR award 08-SC-NICCR-1072, the USDA Forest Service award 13-JV-11330110-081, and the DOE LBNL award DE-AC02-05CH11231.
How to cite: Fischer, M., Katul, G., Noormets, A., Pozníková, G., Domec, J.-C., Orság, M., Trnka, M., and King, J. S.: Evaluating and bridging the flux-variance and surface renewal methods, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9744, https://doi.org/10.5194/egusphere-egu23-9744, 2023.
Tall tower eddy covariance (TTEC) flux measurements are employed to estimate turbulent matter and energy fluxes at landscape scales (e.g. within 1 to 5 km radius around a tower). Virtually all landscapes feature horizontal surface heterogeneity. One main complication for the interpretation of TTEC is the sampling bias by the varying local meteorological conditions. While the wind direction bias can only be considered by the choice of the location of the TTEC, we examine here how the effects of atmospheric stability can be alleviated by sampling from different measurement heights (zm). The objective is to define an optimal set of measurement heights to minimize sampling bias from variation in atmospheric stratification for TTEC long-term flux observation. To our knowledge, this problem has not yet been addressed in the scientific literature.
We used a two years’ dataset from the 122 m tall tower at Risø (Denmark, 55°41'39.15" N, 12°5'17.93" E) and two flux footprint models to develop an objective statistical approach for the definition of a set of measurement heights for optimal sampling of the landscape heterogeneity. The tower is equipped with 3D ultrasonic anemometers in five different heights. The evaluations concern the Eastern sector, which is comprised of a mosaic of land uses, small settlements and comparably sparse road infrastructures.
We define the criteria for optimal landscape flux sampling from the distributions of the source weights (contribution to the measured flux per unit area) sampled in a number of stability classes relative to a frequent unstable stability class as reference. The upper sampling height is set a priory to match measurements and the targeted area; here zm equal to 120 m for the 70% cumulated footprint to stay within a 5 km radius around the tower.
Theoretical analysis with the footprint model shows the limitation of the attempt to compensate for lateral footprint extension at different stabilities, while the longitudinal sampling of the landscape heterogeneity can be maintained more homogeneously by the systematic choice of the measurement height according to atmospheric stability and wind speed.
The results rely on the accuracy of the footprint estimation, which is generally an essential criterion for the interpretation of TTEC measurements in heterogeneous landscapes.
How to cite: Kissas, K., Scheutz, C., and Ibrom, A.: Reducing the effects of weather on the sampling bias in tall tower eddy covariance flux measurements, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15533, https://doi.org/10.5194/egusphere-egu23-15533, 2023.
The boreal biome exchanges large amounts of carbon (C) with the atmosphere and thus significantly affects the global climate. A managed boreal landscape typically consists of various sinks and sources of carbon dioxide (CO2), methane (CH4), and dissolved organic and inorganic carbon (DOC and DIC) across forests with different stand ages, mires, lakes, and streams. Due to the spatial heterogeneity, a full understanding of the landscape-scale C balance requires capturing all C fluxes. Here, we investigate the five-year interannual variability in the net landscape carbon balance (NLCB) by compiling terrestrial and aquatic fluxes of CO2, CH4, DOC, DIC, and harvested C obtained from 2016 to 2020. For that purpose, we applied tall-tower eddy covariance measurements, stream monitoring, and remote sensing of biomass stocks (i.e. harvested C via clearcutting) to estimate the landscape-scale C fluxes across the land-water-atmosphere continuum for an entire boreal catchment (~68 km2) in Sweden. Our results show that this managed boreal forest landscape was a net C sink during 2016-2020 (123 ± 63 g C m-2 yr-1) with the lowest and highest sink-strength occurring during a wet year 2017 (16 g C m-2 yr-1) and a drought year 2019 (182 g C m-2 yr-1), respectively. The net landscape-atmosphere CO2exchange was the dominant component of NLCB, followed by the C export via harvest and streams. We further found that global radiation and vapor pressure deficit regulated the inter-annual variations of NLCB, whereas forest biomass and source area contribution of mires determined its spatial variability. Overall, our multi-year NLCB investigations provide a holistic understanding of the inter-annual variations in NLCB of managed boreal forest landscapes to better evaluate their potential for mitigating climate change.
How to cite: Chi, J., Klosterhalfen, A., Nilsson, M., Laudon, H., Lindroth, A., Kljun, N., Wallerman, J., Fransson, J., Lundmark, T., and Peichl, M.: Five-year inter-annual variation in the net landscape carbon balance of a managed boreal forest landscape in Sweden, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-16012, https://doi.org/10.5194/egusphere-egu23-16012, 2023.
Posters on site: Thu, 27 Apr, 14:00–15:45 | Hall X5
It has been well-recognised that the horizontal advection can modulate the downwind footprint of the urban heat island (UHI). However, limited studies have considered the urban heat advection (UHA) generated from this boundary-layer process, mainly due to the lack of a dense network of sensor to sufficiently resolve the local climate in a city. For the first time, this study explores the possible influence of the horizontal advection on the nocturnal surface urban heat island sensed by the MODIS satellite (sUHA) over a ten-year period. Results show that the heat transport from urban to downwind areas can be observed by the satellite instrument. A significant warming up to 0.5 ºC and 1.7 ºC were found at city (Birmingham) and regional scale (West Midlands area), respectively. The amplification of the sUHA at regional scale was largely attributed to the topography effects according to the significant correlation between sUHA and a topography index (i.e. R2=0.53). An approximate 0.5 ºC can be corrected for sUHA after minimising the topography impact by applying a statistical method. Overall, this study highlighted the value of the satellite instrument to investigate the UHA at both city and regional scale. However, more importantly, the topography was found to have considerable influences on regulating the heat transfer from urban to its downwind areas, which provides further implications for urban planning and risk management with respect to the UHI.
How to cite: Feng, J., Wang, Y., Cai, X., and Chapman, L.: The Effect of Horizontal Advection on the Nocturnal Surface Urban Heat Island Using MODIS Satellite over Birmingham and the West Midlands, United Kingdom, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4605, https://doi.org/10.5194/egusphere-egu23-4605, 2023.
The exposure of populations to toxic traffic emissions is an important concern and significant research effort has been put into measuring and modelling exposure to traffic related pollutants within urban areas. It is also the case that busy trunk roads can pass through villages and towns subjecting those populations to both particulates and pollutant gases. Often, smaller villages in urban areas have complex topographies and provide a different environment to cities with regard to pollutant dynamics. Perfluorocarbon (PFC) trace gases are useful to measure the flow of gases within an area [1]. PFCs are inert, non-depositing and non-toxic and can be detected at low levels using sufficiently sensitive mass spectrometers and preconcentration devices [2]. To understand the passage of gaseous pollutants from a busy road passing through a rural village in Southern England, PFCs were released from a fixed and a moving source and sampled in several locations downwind.
Eight experiments occurred over three different measurement periods, three in June 2021, two in February 2022 and two in May 2022, covering different times of day and meteorological and road conditions. In each experiment, perfluoromethylcyclohexane was released from a fixed position approximately 400 m downwind of the road (July, Feb) or on the road west of the village (May) for 15 minutes, while 1,3-perfluorodimethylcyclohexane was released from the passenger side of a moving vehicle travelling with the flow of traffic through the village. 30-minute Tedlar bag samples were collected in up to 10 locations, some of these locations also measured PM10, PM2.5 and PM1 using an Alphasense N3 optical particle sensor. Bag samples were stored separately from release equipment and transported to Bristol University School of Chemistry for analysis using the methodology described in [3].
Wind directions during the experiments were south westerly and westerly. The highest tracer concentrations from the moving source were often measured within a bus stop roadside in the centre of the village, whereas the static release was highest at a residential roadside sample on the western side of the village. Two samples were taken roadside in a church yard and at the top of the spire, the moving release was consistently higher at ground level, but from the stationary release the tracer was predominantly higher in concentration at roof height.
[1] Shallcross, D. E. et al. 2009. Atmospheric Science Letters, 10(2), 59-65.
[2] Simmonds, P. G. et al .1995. Analytical Chemistry, 67(4), 717-723.
[3] Matthews, J. C. et al. 2020. Boundary-Layer Meteorology, 175(1), 113-134.
How to cite: Matthews, J., Khan, A., and Shallcross, D.: Mapping of traffic emissions from a busy road in a rural village using gaseous perfluorocarbon tracers, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10175, https://doi.org/10.5194/egusphere-egu23-10175, 2023.
Globally, cities correspond to most of the direct anthropogenic carbon emissions, and due to the global mega-trend of urbanization, their importance will only increase. The carbon budget of an area is often given as a net ecosystem exchange (NEE), which describes net CO2 fluxes measured with eddy covariance (EC) method. However, these measurements alone cannot partition anthropogenic and biogenic carbon sources and sinks. Earlier studies on vegetated ecosystems have defined leaf-scale relative uptake (LRU) of carbonyl sulfide (COS) and CO2 to partition the biogenic uptake, namely gross primary production (GPP).
In this research, the aim was to examine the suitability of using COS flux measurements to partition GPP from urban NEE, to better understand the effect of urban green areas on the carbon balance of cities. EC fluxes of CO2 and COS were measured at ICOS Associated Ecosystem Station FI-Kmp station in Helsinki, Finland, during Winter 2020-2021 and July 2022. Urban LRU is estimated for a footprint dominated by urban parks. Then, GPP is estimated from the measured COS flux, using three methods with varying complexity, for more heterogeneous footprints with more pronounced anthropogenic influence. Estimates are compared with a more common carbon balance partitioning method where only ecosystem respiration is considered.
Preliminary results showed how LRU over urban park has similar behavior as forest LRU, and the values are same order of magnitude. COS flux can be used as a tracer for carbon uptake by photosynthesis also in urban areas. Two out of the three methods showed the daily dynamics of GPP qualitatively right, with more complex underestimating and simpler overestimating the GPP, respectively. When using COS as a proxy for GPP in a heterogeneous urban environment, errors arise due to anthropogenic emissions of COS, which are not expected in the original context of using the compound as a biogenic activity tracer. In the future, more focus will be put to adapt methods to determine anthropogenic influence.
How to cite: Soininen, J., Rantala, P., Kulmala, L., and Järvi, L.: Partitioning the urban carbon budget with carbonyl sulfide (COS) flux measurements conducted in a high-latitude city, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7420, https://doi.org/10.5194/egusphere-egu23-7420, 2023.
This study summarizes seasonal monitoring of turbulent energy fluxes from eddy covariance (EC) and large aperture optical scintillometer, measuring in parallel. The site (agricultural field of app. 16.5 ha) is located in north-eastern Austria, Danube river lowland (48.21N, 16.622E); in 2019 covered subsequently by a winter wheat field, straw, and bare soil. The EC together with ancillary measurement was located at the 2.7 m height at the center of the field. The radiation balance components measurements consist of a 4-channel net radiometer for net radiation (Rn) installed at 3.5 m and three soil heat flux plates for soil heat flux (G) monitoring (0.05 m below surface), including thermocouples for quantification of the heat storage above the soil heat flux plates. The scintillometer transmitter and receiver units were fixed at 4 m height masts, facing towards each other from the NW and SE corners of the field, with a measurement path length of 570 m diagonally across the field. The EC method enables the determination of fluxes within a footprint centered around the point of measurement in the middle of the field, whereas the scintillometer provides an estimation of sensible heat flux (HSC), derived from air refractive index fluctuation integrated over the measurement path length. The scintillometer-based latent heat (LESC) is calculated as a residuum from available energy (Rn-G) and HSC, provided by the scintillometer. As the EC method provides direct measurements of sensible heat (HEC) and latent heat (LEEC) fluxes we use it as a reference method. During the period March to June (green canopy) the comparison of the EC-based turbulent fluxes (HEC+LEEC) and the available energy (Rn-G) showed a very good agreement, resulting in the energy balance closure of 0.97 (R2 = 0.94). This suggests the ability of the EC method to capture all scales of eddies responsible for energy transport at this site as well as the good accuracy and robustness of the measurement setup. During the period March to June (green canopy), the HEC, LEEC, HSC, and G fluxes accounted for 23 % (R2 = 0.55), 60 % (R2 = 0.72), 32 % (R2 = 0.56), and 12 % (R2 = 0.62) of the Rn flux, respectively. The comparison of methods indicates that HSC overestimated HEC by 20 % (R2 = 0.78). However, during the latter part of the season (straw and bare soil) we found that under highly unstable atmospheric stratification, HSC is even more overestimating HEC and sometimes is even exceeding the available energy. The main reason for such behavior can be the choice of the universal stability function in the computation of HSC. Recommendations for universal functions that are correcting this artifact in HSC will be discussed.
Acknowledgment: This study was supported by SustES - Adaptation strategies for sustainable ecosystem services and food security under adverse environmental conditions (CZ.02.1.01/0.0/0.0/16_019/0000797).
How to cite: Orság, M., Fischer, M., Pozníková, G., Eitzinger, J., and Trnka, M.: Comparison of the energy fluxes inferred from eddy covariance and optical scintillometer at the agricultural field during different parts of the season, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7132, https://doi.org/10.5194/egusphere-egu23-7132, 2023.
Agroforestry (AF) systems are recognized as a more sustainable agricultural practice compared to conventional agriculture due to its potential for increase carbon sequestration, among others. Short Rotation Alley Cropping (SRAC) is an AF practice in Central Europe in which trees and crops are cultivated in alternating rows.
The amount of carbon sequestered by a SRAC system can be estimated by the eddy covariance (EC) technique, the standard method for the continuous assessment of energy, momentum and trace gas exchanges above terrestrial ecosystems. As SRAC systems are heterogeneous, using only one EC set-up might limit the spatial representativity and, hence, the statistical power of measured fluxes. Increasing the number of EC set-ups could increase the statistical power, which is, however, cost intensive.
Therefore, the aim of this study was to test (i) the performance of a lower-cost EC (LC-EC) set-up for CO2- and H2O-flux measurements above SRAC and monocropping (MC) agriculture and (ii) if the sensor-to-sensor differences in fluxes are lower than differences between ecosystems (SRAC and MC).
We performed CO2 and H2O flux measurements above a MC system with three lower-cost and one conventional EC set-up from March to August 2022. In addition, CO2 and H2O fluxes were also measured with a LC-EC set-up located in a SRAC system at 520 m distance from the MC site.
The CO2 and latent heat (LE) fluxes of the three LC-EC set-ups showed similar results compared to the conventional EC setup. The linear regression between the conventional and the LC systems showed R2 coefficients in the range of 0.8-0.9 for CO2 and 0.7-0.9 for LE, and slopes in the range of 0.9-1.0 for CO2 and 0.8-1.0 for LE. The energy balance was consistent for all the systems, providing an average 70% closure. The total cumulative C uptake over the entire campaign was similar among the 3 LC-EC set-ups, but they underestimated the C uptake compared to the conventional EC set-up by 18% on average. The C uptake measured by the LC-EC systems at the end of the measuring campaign was 74 g C·m-2 at the MC (mean across all the 3 LC-EC set-ups) and 111 g C·m-2 at the SRAC. The C uptake of the conventional EC system at the MC was 90 g C·m-2. Hence, the SRAC system had a larger C uptake than the MC system throughout the measurement campaign.
We conclude that the LC-EC provided satisfying results compared to conventional EC, with the potential to improve the spatial replication of EC measurements. Furthermore, the difference between the 3 LC-EC set-ups in the MC was much lower compared to the difference between the MC and the SRAC.
How to cite: Callejas Rodelas, J. Á., van Ramshorst, J., Knohl, A., and Markwitz, C.: Intercomparison of lower-cost and conventional eddy covariance systems for CO2 and H2O flux measurements above cropland monoculture and agroforestry, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-1527, https://doi.org/10.5194/egusphere-egu23-1527, 2023.
Temperate forests have been shown to substantially impact near-surface climate and atmospheric boundary layer dynamics through a range of complex land-atmosphere feedback mechanisms. For example, forests can reduce water loss to the atmosphere during periods of high vapour pressure deficit, thereby preventing or delaying severe drought impacts. Reducing water loss during periods of high atmospheric water demand comes at the expense of reduced forest productivity and may contribute to additional warming of near-surface air temperatures through increased partitioning of energy to sensible heat. Understanding how land-atmosphere interactions in forested landscapes modify regional and local climate is thus crucial for the design of efficient national and international climate mitigation and adaptation strategies.
To better understand complex land-atmosphere interactions in a typical forested landscape of eastern Canada, we have established an integrated atmospheric boundary layer observatory in a temperate forest in New Brunswick, Canada. Observations will be used to quantify environmental, plant physiological, and atmospheric feedbacks and their impacts on near-surface climate. Here, we present the instrumental setup and preliminary results from the integrated observatory. Forest soils are monitored using soil temperature, volumetric soil moisture, soil water potential, and snow depth measurements and are complemented by soil CO2 efflux measurements using forced diffusion chamber systems. Detailed vertical profiles of air temperature and humidity, wind speed and direction, and light are measured from the forest floor to a height of 28 m (i.e., 18 m above the forest canopy) using six weather stations. At the top of the flux tower at 28 m above ground, net ecosystem CO2 exchange and evapotranspiration of the forested landscape is measured using the eddy covariance technique along with longwave and shortwave radiation fluxes. A ceilometer will be added to the observatory in spring 2023 to continuously observe cloud base height and atmospheric boundary layer height. The integrated measurements will produce datasets that can be used to diagnose complex land-atmosphere interactions, to characterise forest microclimate, and to validate coupled land-atmosphere models.
How to cite: Helbig, M., Nick, N., Deklan, M., Lukas, R., Jillian, R., Lidia, B.-V., Chance, C., and Mara, T.: From soils to clouds - An integrated atmospheric boundary layer observatory in a temperate forest of eastern Canada, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3707, https://doi.org/10.5194/egusphere-egu23-3707, 2023.
Ecosystems play an important role in controlling the exchange of energy, water and carbon between the land surface and the atmosphere, which contributes to the regulation of the climate through biogeochemical process. Changes in vegetation or biomass impacts the microclimatological conditions of the landscapes with feedbacks to the heat and water budgets. Knowledge about the dynamics and driving factors of the exchange processes contributes to our understanding of the land surface – atmosphere interactions as drivers of the Earth’s surface energy budget.
In the Tumbesian mountain dry forest (MDF) in the Laipuna reserve on the western escarpment of the Andes mountains in South Ecuador two eddy-covariance measurement stations have been installed over natural forest and an anthropogenic replacement system to observe atmospheric water and carbon fluxes. The MDF is characterized by a distinct seasonality, which can be divided into a dry (May - December) and wet (November - May) season following the inter-hemispherical shift of the ITCZ. Mean monthly precipitation totals ranges between 50 and 400mm with an annual amount of 650mm, while the temperature varies between 21 – 26°C. The forest ecosystem is dominated by deciduous trees and hold a clear annual cycle in the water budget and carbon sequestration. In the scope of global climate change such water limited landscapes are strongly vulnerable to climatic stress situations which lead to changes in the phenological cycles in the ecosystem associated with feedbacks to the water and carbon cycle. The aim is thus, to investigate the energy, water and carbon dynamics along a land use gradient in order to estimate the impact of deforestation on net-ecosystem exchange and evapotranspiration in the MDF region. The study shows first results of microclimatological conditions, such as radiative fluxes, moisture and soil conditions of both sites as well as water and carbon fluxes.
How to cite: Murkute, C., Cofrep, F. P., Raffelsbauer, V., Scholz, S., Limberger, O., Carillo-Rojas, G., Bendix, J., and Trachte, K.: Water and carbon fluxes along a land use gradient in the tropical mountain dry forest of South Ecuador, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-5832, https://doi.org/10.5194/egusphere-egu23-5832, 2023.
Thinning is performed primarily to manage between-tree competition and allocate growth-limiting resources (e.g. light, water, nutrients) to the remaining trees and to increase their growth rate and vitality. From biophysical point of view, thinning changes tree spacing, number, and size distribution. Our hypothesis is that altered stand structure and decreased foliage density cause modifications of the microclimate, radiation budget and turbulence characteristics within the canopy. Jointly, these physical constraints change the dynamics of biogeochemical cycles and affect mass and energy exchange between soil and vegetation components and the atmosphere.
Here, we investigate the short-term response (i.e. one-two years post thinning) to the thinning done at Hyytiälä forest located in southern Finland. We present results using eddy covariance (EC) fluxes of NEE and ET at both ecosystem level (i.e. above canopy EC) and ground vegetation level (i.e. sub-canopy EC). We found that the forest became a source of carbon during the first post thinning year (+55 gC m-2), while in the second post-thinning year (2021), the ecosystem has only partly recovered showing annual NEE value of -152 gC m-2 which is somehow far from the long-term net uptake measured at the site (-252 gC m-2). Preliminary results show that the thinning had less impacts on ET fluxes. We also report the effect of thinning on ecosystem surface fluxes of carbonyl sulfide (COS), carbon monoxide (CO) and ozone (O3). Here, we hypothesize an increase of CO biogenic emission, due to an increase of amount of litter and light on the forest floor, and a decrease of COS and O3 deposition rates, related to foliage removal.
Finally, the functional response of the flux components are analysed by using clustering and modelling approaches in order to disentangle the roles of thinning and weather on measured fluxes and budgets.
How to cite: Mammarella, I., Thomas, A., Aslan, T., Aalto, J., Back, J., Kolari, P., Launiainen, S., Peltola, O., and Vesala, T.: Effect of thinning on turbulence structure, energy and gas exchange in a boreal forest, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12230, https://doi.org/10.5194/egusphere-egu23-12230, 2023.
Exchanges of mass and energy between a subalpine coniferous forest and the atmosphere have been continuously monitored since few decades at Renon (Bolzano, Italy) applying the eddy covariance (EC) technique. The station is part of the Integrated Carbon Observation System (ICOS) EU Research Infrastructure. The area surrounding the site is characterized by complex topography, with a mean slope angle of about 11° and a Southward aspect. In this study, we focused on the analysis of turbulent energy fluxes (sensible and latent heat) and the energy budget closure of the forest during a period of about three months (August-October 2021), when a below-canopy EC system was additionally deployed to better understand the dynamics of turbulent exchanges. The energy balance closure was assessed for periods characterized by distinct wind circulation patterns (thermally-driven slope winds vs. synoptic winds) and turbulent energy fluxes were processed applying different coordinate rotation methods (double rotation and planar fit). We found significant differences in the magnitude of sensible and latent heat fluxes computed with double rotation or planar fit. These differences were more marked during periods characterized by slope winds, suggesting a connection with local advection performed by these winds.
How to cite: Vendrame, N., Destro, M., Rodeghiero, M., Montagnani, L., and Zardi, D.: Turbulent energy fluxes and surface energy balance closure of a coniferous forest at the complex-terrain site of Renon (Italian Alps), EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15305, https://doi.org/10.5194/egusphere-egu23-15305, 2023.
Forests cover roughly one third of the global land area and currently remove around one quarter of anthropogenic CO2 emissions, thus slowing down the increase in atmospheric CO2 concentrations. Forests account for approximately 90% of all terrestrial biomass, which corresponds to about 400 Gt C.
However, the ratio of carbon uptake to release is a very fragile one and is determined by many factors such as water and nutrient availability, the amount and quality of light or stand age. In addition to the factors mentioned above, temperature is one of the most important factors that determine this ratio. Both fluxes determining the net ecosystem exchange (NEE), the gross uptake of CO2 by photosynthesis (GPP) and ecosystem respiration (Reco) are sensitive to temperature. Thus, we investigated the temperature sensitivity of NEE at a newly established pine forest field site in Austria at 960 m a.s.l. Applying an understory and an ecosystem scale eddy covariance system we were able to disentangle temperature effects on understory and tree crown CO2 exchange.
We found a clear temperature optimum for CO2 uptake on ecosystem scale at around 20°C and a decrease in uptake on higher temperatures. This decrease was caused by (i) the understory turning from a slight sink for CO2 into a source of CO2 at higher temperatures, and (ii) a reduction of CO2 uptake in the tree canopy layer. Furthermore, we compared carbon flux data with continuous tree growth data from dendrometer measurements.
How to cite: Hammerle, A., Spielmann, F., Scholz, K., Oberhuber, W., and Wohlfahrt, G.: Some forests like it cold, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15468, https://doi.org/10.5194/egusphere-egu23-15468, 2023.
The eddy covariance technique (EC) is used worldwide to measure surface fluxes of greenhouse
gases and energy balance components. Nevertheless, in the scientific community it is well-known
that EC presents an imbalance of the energy components. In this regard, the atmospheric boundary
layer (ABL) directly influences the mass and energy transfer between surface and atmosphere.
Thus, knowledge and characterization of the ABL might be essential to disentangling the drivers
causing the imbalance of the energy components measured by EC. This work aims to relate ABL
characteristics to the accuracy of the surface energy balance closure (SEBC) obtained by EC.
The study was carried out in an irrigated olive orchard (Olea europaea var. europaea L.) in the
Southeastern Iberian Peninsula (37.9427º N, 3.3002º W and 370 m asl) during the intensive
BLOOM (turBulence and oLea pOllen prOperties experiMent) campaign, from May 19th to June
20th 2022. In order to characterise ABL dynamics, remote sensing techniques are commonly used.
One of them is via Doppler lidar, which provides measurements of wind components and
turbulence-related products at high spatial and temporal resolutions. In particular, a Doppler lidar
Stream Line (HALO photonics) with a temporal resolution of 2 seconds and 10 minutes (for vertical
and scanning measurements, respectively) and 30 m of vertical spatial resolution was used to
retrieve the turbulent kinetic energy dissipation rate (ε) and wind shear (sh) with a common
resolution of 3 minutes as indicators of convective and mechanical sources of turbulence,
respectively. To assess the SEBC, we used (1) a three-axis sonic anemometer (CSAT-3, Campbell
Scientific, Logan, UT, USA) and an enclosed path infrared gas analyser (IRGA, Li-Cor 7200;
Lincoln, NE, USA) on a tower 9 m tall to measure latent heat (λE) and sensible heat (H) fluxes; (2)
an incoming and outgoing short- and long-wave 4-component radiometer (CNR-4, Kipp & Zonen,
Delft, Netherlands) to measure net radiation (Rn); and (3) two each: soil moisture probes (CS616,
CSI), thermocouples (TCAV, CSI) and heat flux plates (HFP01, Hukseflux, Delft, the Netherlands)
at 0.10 m, 0.04 m and 0.08 m depth, respectively to calculate the soil heat flux (G).
Preliminary results show that SEBC enhances under turbulent conditions (slope and R2 from 0.49
and 0.92 to 0.81 and 0.94, respectively). However, when the source of turbulence is mechanical the
SEBC is less accurate (slope and R2 from 0.82 and 0.94 to 0.77 and 0.9, respectively). A more
detailed study based on principal component analysis of the ABL height, skewness of the vertical
wind velocity and vertical profile of horizontal wind, together with ε and sh, among other Dopplerlidar-
derived products is expected to offer reliable information that is highly relevant regarding the
influence of the ABL on the SEBC.
ACKNOWLEDGMENTS: This work was supported by the
Spanish Ministry of Science and Innovation through project PID2020-117825GB-C21
(INTEGRATYON3), the Andalusian regional Development through the projects B-RNM-60-
UGR20 (OLEAGEIs) and P18-RT-3629 (ICAERSA), including European Union ERDF funds.
How to cite: Aguirre García, S. D., Andújar-Maqueda, J., Abril-Gago, J., Aranda- Barranco, S., Agea-Plaza, D., Ortiz-Amezcua, P., Sánchez-Cañete, E. P., Kowalski, A.-S., Serrano-Ortiz, P., and Guerrero-Rascado, J.-L.: Studying the Atmospheric Boundary Layer influence on the Surface EnergyBalance Closure combining eddy covariance and Doppler lidar, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-17499, https://doi.org/10.5194/egusphere-egu23-17499, 2023.
Accurate observations of atmospheric composition and exchange of greenhouse gases between the ecosystems and the atmosphere are critical for constraining climate models. Infrared gas analyzers (IRGA) using either broad band non-dispersive or narrow band tunable laser technologies are widely used for this purpose. Typically, such analyzers are installed on stationary meteorological towers over land; but an increasing number of systems are being deployed on mobile platforms and buoys to extend the spatial coverage and include measurements over water. One technological challenge is that the motion of the platform influences the gas concentration measurements. Empirical correction methods have been proposed, but their universality is limited because the source of these sensor-related effects and their underlining mechanisms have not been understood. In this study we identified the dominant source of the error: orientation-dependent temperature stabilization of the thermoelectrically cooled infrared detector. To further investigate this hypothesis and gain insights to a solution, a new prototype closed-path IRGA with an improved infrared detector was developed. In the study, we compared the performance of the prototype to standard models of commercially available IRGA measuring CO2 and H2O. Tilt experiments with side-by-side mounted IRGAs were first conducted on a controlled laboratory platform with independent pitch and roll axes. Over the ±30° range of angular position, the orientation-correlated errors were reduced by a factor of 4 to 10 on CO2 and a factor of 2 to 8 on H2O. Subsequent testing was performed duplicating realistic buoy motion in a deep-water tank with typical at-sea combined pitch and roll motion. In these tests, improvements in the measurement errors were similar to the laboratory experiments. Implications for the correction of past field measurements and insights for further sensor optimization and system improvements are discussed.
How to cite: Bogoev, I., Vandemark, D., Emond, M., Miller, S., Shellito, S., and Covert, J.: Improvements in infrared gas analyzers for measuring atmospheric gases on moving platforms, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3987, https://doi.org/10.5194/egusphere-egu23-3987, 2023.
Absorption, transformation and release of incoming solar radiation as turbulent heat into the atmosphere is critical for earth's energy balance. However, there is a lack of knowledge of the governing factors of the associated turbulent fluxes. Especially the influence of land surface heterogeneities is uncertain, as often only one-dimensional measurements are available. Finding an interrelation of the surrounding terrain to the turbulent fluxes is therefore not possible. This might be the explanation for why measured fluxes often cannot be reproduced with common calculation methods.
Thus, the objective of our study is to investigate the impact of surface heterogeneities on turbulent surface fluxes by performing idealized Large Eddy Simulations of a convective boundary layer over heterogeneous land surfaces under varying conditions. The simulations are run with the Parallelized Large-Eddy Simulation Model (PALM), covering a 10 km x 10 km domain with cyclic boundary conditions. The horizontal resolution is 5 m, the vertical resolution is 2 m near the surface and is increasing with height. The simulation period is one day. The scenarios differ in initial wind profiles, radiation, soil moisture and the type of surface heterogeneities. Output variables are averaged over 5 minutes.
By means of these highly resolved simulations, an encompassing three-dimensional analysis of the turbulent surface fluxes and their governing factors could be carried out, enabling the development of improved methods for calculating turbulent fluxes.
How to cite: Koerner, B.: High resolution Large Eddy Simulations of the convective boundary layer over idealized land surface heterogeneities, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7621, https://doi.org/10.5194/egusphere-egu23-7621, 2023.
In parameterization of the bi-directional ammonia exchange models over vegetated surfaces there are three most crucial parameters: (1) the stomatal (χs) and (2) the soil (χg) compensation point concentrations as the function of Γ=[NH4+]/[H+] in the apoplast and soil, as well as (3) the cuticular resistance Rw. These factors determine the direction and magnitude of the ammonia flux. Moreover, in the sophisticated models the soil (Fg) and litter (Fl) fluxes must be distinguished as well. Furthermore, the recapture of ammonia volatilized from the ground in the lower layer of the canopy should also be considered.
For partitioning the measured ammonia flux into stomatal, cuticular and ground parts two-layer, bi-directional exchange models are generally used. However, the parameterization mostly based on empirical relationships involves uncertainties, resulting in disagreements among the applied models in the estimation of the stomatal/soil flux ratio.
The main reasons of the deviations may be the following:
- a) Overestimation of the soil compensation-point (χg).The Γg calculated from the ammonium content of the soil and the pH of the soil solution is overestimated, because part of the ammonium content in the soil is bound in the solid phase hence Henry's law for the liquid phase cannot be applied for this fraction.
- b) Neglecting of the part of soil derived ammonia recaptured by leaves. For this reason, soil emissions may be underestimated.
- c) Uncertainty or lack of bioassay measurement for Γs and difficulties with the Γs determined by indirect way. Instead of complicated bioassay measurements, the models generally use empirical approximations to calculate the stomatal compensation point concentration or infer it from the bulk ammonium content of the leaf tissue. Both methods can be a source of error.
- d) Inaccurate or rough estimate of cuticular resistance. Beside the temperature and humidity, the ratio of acidic air components and ammonia determines the Rw. Models often consider a constant site-specific average for this parameter, even though the ratio of acidic substances to ammonia varies from day to day.
Due to these uncertainties, the estimation of the share of fluxes controlled by soil and vegetation is often uncertain. Furthermore, the uncertainty of the parameterization limits the applicability of the model and reduces its robustness.
As a conception, we are aiming the use of the following measurement and parameterisation protocol:
- a) Measurement of the flux above bare soil and above the litter covered soil separately, by soil chambers using the PICARRO-G2103 NH3 Hence, the Fg and Fl and the ratio of compensation point concentrations (χg/χl) can be estimated separately. Comparison of the χg calculated from soil NH4+ and pH with the measured values.
- b) Calculation of the recaptured ammonia by the model as the residual term among soil-cuticular-stomatal exchange.
- c) Performing bioassay measurements.
- d) Use of daily acid/base gas ratio from the nearby regional background air pollution station.
Model conception based on previously developed models. Bulk fluxes above the canopy will be measured by the relaxed eddy accumulation technique (REA) with a newly designed photoacoustic system using a QCL as light source.
How to cite: Horváth, L., Huszár, H., Nagy, Z., Pintér, K., Szabó, A., Takács, T., Torma, P., Tóth, E., Weidinger, T., and Bozóki, Z.: Application of a bi-directional ammonia exchange model for optimization of input parameters at a fertilized crop system; validation by flux measurements, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-5854, https://doi.org/10.5194/egusphere-egu23-5854, 2023.
Micrometeorological measurements, and greenhouse-gas monitoring, performed by on-site sensors or remote sensing are not exclusively influenced by the terrain beneath the sensor position or at the optically aimed spot, sometimes they are not even influenced by it at all. The footprint function (or so-called source area) provides a description of the actual “field of view”, namely the 2D spatial distribution of the weighing function applied on the sources and sinks to yield the signal value. Given a scalar of interest, different distributions are obtained depending on whether the considered quantity is the concentration or the flux of this scalar.
Footprints derived from fully analytical models are restricted due to the following hypotheses: homogeneous flow (i.e. in terms of soil-atmosphere interactions, e.g. roughness length, thermal sources driving the turbulence), the eddy diffusivity and the mean wind speed are power-law functions of height. Despite these restrictions, they are often used due to their ease and speed. The footprint functions are expressed in terms of the inverse Gamma distribution whose parameters depend on the power-law parameters. These parameters must be identified from the actual wind speed and diffusivity profiles, which are generally assimilated to profiles parameterized according to the Monin-Obukov theory. The scope of the analytical approach can be broadened by relaxing the power-law constraint regarding the profiles. In this perspective a new semi-analytical model was developed which is based on a graded multi-layer approach. A Liouville transformation is first applied which introduces a new independent variable, the Diffusion-Ascent-Associated Advection Distance (DAAAD, in place of height) and a new advection-diffusion parameter, the atmosphere inertivity, which describes the atmosphere inertia to state change at the considered position. The graded multi-layer method allows approximating the real inertivity profile by a piecewise function, with continuously joined sublayers, hence allowing a close fitting with a minimal number of sub-layers.
As an example, Monin-Obukhov profiles based on the Businger-Högström parameterization, from unstable to stable, were considered and the footprint functions were computed for a large range of height. It was shown that the corresponding concentration and flux footprints are very accurately approximated (to less than 1-1.2% RMS error) by the functions mentioned before based on the inverse Gamma distribution. The optimal values of the two or three parameters involved therein were computed to provide a database depending on the two ratios zm/z0 and z0/L. Furthermore, an analytical parameterization of the two parameters intervening in the flux footprint has been proposed with only a slight reduction of the performance as compared to the highly accurate semi-analytical multi-layer model.
A comparison to the classical Kormann & Meixner, and Hsieh et al. models, which otherwise share the same hypotheses, is finally presented. With a negligibly small increased effort in the computation of the parameterization functions, a much better rendering of the Monin-Obukhov footprints is achieved. Moreover, the Monin-Obukhov profiles are just an example, the graded multi-layer method can be applied to any pair of profiles inasmuch the K-theory can be considered valid in the studied context.
How to cite: Krapez, J.-C.: Footprint parameterization derived from a graded multilayer semi-analytical model valid in homogeneously driven boundary layers described by Monin-Obukhov theory, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7164, https://doi.org/10.5194/egusphere-egu23-7164, 2023.
Water scarcity is regarded as a primary issue in many dry climates, with significant impacts on food security and national developments. Since agricultural irrigation accounts for most of water consumption worldwide, providing a water management system is critical to cope with water stress and its challenges. Agricultural water management is an interdisciplinary task, dealing with meteorological and environmental factors. In this work, we have established a 24/7 operational system to simulate those land surface variables, associated with evapotranspiration, biomass growth, and water deficit, using the Surface Energy Balance Algorithm for Land (SEBAL). SEBAL simulates the energy balance, using satellite data in shortwave and thermal bands, as well as soil and meteorological data (wind speed, humidity, etc).
This workflow consists of 3 interconnected units: WRF model, Python implementation of the SEBAL model (pySEBAL), and a web-based management panel for the visualization, reanalysis, and publishing the results. The WRF model is run in a daily basis for 36 hours, starting from 12:00 UTC, to provide the meteorological data for the next day. At the next stage, the simulated WRF data after some required processing (converting formats and units of files and
variables, etc.) will be incorporated as input data into the SEBAL model. The key data for the SEBAL model is the “Visible Infrared Imaging Radiometer
Suite” (VIIRS) real-time data over the Suomi satellite, which is received automatically after tracking the satellite and picking the appropriate data files for download. SEBAL outputs include some of the variables with key role in agricultural water management, such as actual and potential evapotranspiration, biomass production and deficit, albedo, NDVI, etc, with a resolution of 375m over Iran.
The third section of the operational system is a web-based panel, consisting of an open-source server to share and edit the SEBAL outputs. An open-source database management system for the client- based analysis of the SEBAL outputs, and an open-source JavaScript library for displaying the maps of the SEBAL outputs in web browsers.
How to cite: Nikfal, A., Karimi, M., Pashapour, S., Vazifedoust, M., Khorani, M., Khosravi Tabrizi, A., Noory, H., Rezvani, M., and Toofaninejad, Z.: A new 24/7 operational workflow in agro-meteorology, based on the coupled WRF/SEBAL models, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-1901, https://doi.org/10.5194/egusphere-egu23-1901, 2023.
Undisrupted wind observations at 10m level (u10, v10) have been analyzed for recent decadal changes with respect to surface geostrophic winds (ug, vg) and 10m winds from ERA5 (u10E, v10E).
Thus, we analyze the difference between (u10, v10) and (ug, vg), and between (u10, v10) and (u10E, v10E). The underlying hypothesis is that the effective roughness length has increased during the last 30 years in the Danish area, including surrounding seas, due to the extensive expansion of both on- and off-shore wind turbine installations in Denmark and neighboring countries.
Theoretically a gradual increase in roughness length will lead to a reduction in near-surface winds with respect to undisturbed conditions, i.e., the recent "climatic roughness length" before the present analysis. We already know from extensive measurement campaigns - mostly offshore - that direct wake effects from large wind farms can be quite substantial - with reduced near surface wind - in the wake, sometimes up to almost 100 km downstream of the wind farm.
Furthermore, the cross-isobaric flow will change, resulting in a potential enhanced Ekman pumping in the planetary boundary layer, and thereby an accelerated spin down process of atmospheric synoptic scale weather systems, including induced precipitation in decaying low-pressure systems. Therefore, this is also analyzed.
It is well known that we have natural decadal and interdecadal fluctuations in the near surface wind, which are not related to changing regional surface characteristics. This is the reason that we do not consider the direct wind-observations but rather the anomalies with respect to ERA5 surface geostrophic winds and near surface winds, which are only marginally "polluted" by the existence of wind farms, since these are not build into the re-analysis system (model)
We have obtained results showing a change in the wind characteristics analyzed, which is in line with the original hypothesis.
How to cite: Kaas, E., Vedel, H., and Fischereit, J.: Observed changes in ageostrophic winds over Denmark, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13590, https://doi.org/10.5194/egusphere-egu23-13590, 2023.
Eddy covariance flux measurements need to be gap-filled when utilising the data for the calculation of annual balances. The measurement technique itself is prone to errors and technical failures may also lead to gaps of various lengths. Gap-filling of the flux time series is typically based on estimating statistically representative values based on various environmental variables through linear regression, lookup tables or machine learning methods.
A large number of methods for the imputation of energy fluxes have been applied and compared in recent literature (Zhu et al. 2022; Mahabbati 2022; Khan, Jeon, and Jeong 2021; Foltýnová, Fischer, and McGloin 2019). Both latent and sensible heat fluxes are strongly driven by the incoming solar radiation, and it is usually used as an independent variable in gap-filling models. Vekuri et al. showed that a widely used method for gap-filling carbon dioxide fluxes creates a systematic bias in northern ecosystems, where the distribution of incoming radiation is highly skewed.
Here, we assess if a similar bias error emerges for sensible and latent heat fluxes after gap-filling with the standard methods or suggested alternatives. We use global data from openly available flux measurement databases and compare the bias and other metrics between different latitudes. We assume that the errors in total energy balances are not as significant as in carbon budgets, but the results could still indicate which methods should be preferred when complete time series of energy flux data are needed.
References
Foltýnová, L., M. Fischer, and R.P. McGloin, ‘Recommendations for Gap-Filling Eddy Covariance Latent Heat Flux Measurements Using Marginal Distribution Sampling’, Theoretical and Applied Climatology, Vol. 139, No. 1–2, September 11, 2019, pp. 677–688.
Khan, M.S., S.B. Jeon, and M.-H. Jeong, ‘Gap-Filling Eddy Covariance Latent Heat Flux: Inter-Comparison of Four Machine Learning Model Predictions and Uncertainties in Forest Ecosystem’, Remote Sensing, Vol. 13, No. 24, January 2021, p. 4976.
Mahabbati, A., ‘Investigating the Application of Machine Learning Models to Improve the Eddy Covariance Data Gap- Filling’, The University of Western Australia, 2022.
Vekuri, H., J.-P. Tuovinen, L. Kulmala, D. Papale, P. Kolari, M. Aurela, T. Laurila, J. Liski, and A. Lohila, ‘A Widely-Used Eddy Covariance Gap-Filling Method Creates Systematic Bias in Carbon Balance Estimates’, Scientific Reports, forthcomig.
Zhu, S., R. Clement, J. McCalmont, C.A. Davies, and T. Hill, ‘Stable Gap-Filling for Longer Eddy Covariance Data Gaps: A Globally Validated Machine-Learning Approach for Carbon Dioxide, Water, and Energy Fluxes’, Agricultural and Forest Meteorology, Vol. 314, March 1, 2022, p. 108777.
How to cite: Rinne, E., Vekuri, H., Tuovinen, J.-P., and Aurela, M.: A comparison of methods for gap-filling sensible and latent heat fluxes in different climatic conditions, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12035, https://doi.org/10.5194/egusphere-egu23-12035, 2023.
Posters virtual: Thu, 27 Apr, 14:00–15:45 | vHall AS
Today, peatlands only cover slightly more than 3.5 % of Germanys territory. However, they play an important role concerning greenhouse gas emissions (CO2, CH4). We can avoid most of these emissions by proper management of the water table. This leads to a large potential net benefit for climate mitigation when re-establishing valuable long-term carbon sinks at the same time. Measurements in peatlands are challenging because they are often situated in remote locations, and it is difficult to install measurement towers on these statically unstable soils.
Two wetlands in Germany (grey willow in NE Germany; black alder in Eastern Brandenburg) are compared to the TU Dresden cluster of sites close to Dresden. The wetlands receive comparatively little precipitation, e.g. the grey willow site receives on average 580 mm/year (average from 1991 – 2020) but the water table is dominated by the nearby river Peene (fluctuating in dependence of the hydrological conditions in its estuary area). Similar complexity exists for the black alder site with regard to the managed water table of the river Spree. Measurements are available from eddy-covariance since 2010 for the grey willow, and from 2010 to 2015 for the black alder.
Yearly, seasonal and daily data of CO2 (gross primary production, ecosystem respiration) and H2O are analysed relative to the water table and the climate forcing (radiation, vapour pressure deficit and wind). Special attention will be paid to the flux patterns at each site (fingerprints of ET, FC and of WUE). A comparison to the long-term cluster sites (forests, grassland and crop rotation) allows a first assessment of the potential benefit of various land management systems for climate mitigation. However, uncertainty might be large due to the differences in soil and climate, as well as by the typical non-linearity of complex systems like the wetlands and their dependence to the water table.
How to cite: Moderow, U., Grünwald, T., Körner, P., Bernhofer, C., and Mauder, M.: Comparing CO2 and H2O exchange of wetlands (high water table) to crops/forests (low water table), EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9061, https://doi.org/10.5194/egusphere-egu23-9061, 2023.
The thunderstorms produce cold pools that spread horizontally few kms from the location of cumulonimbus clouds. They are often seen during the noon-evening period. The atmosphere and several surface meteorological parameters show a sudden change during the passage of these cold pools. An earlier study has noted that 85% of gust events observed at Gadanki, India are associated with these cold pools (and thunderstorms). Cold Pools are mainly found to occur in the months of April, May and June during 11 years’ time from 2010 -2021 over Gadanki. A total of 84 cases of cold pools were seen during this period with highest number of cold pools occurring in the noon-evening time 3 pm- 4 pm, followed by the time intervals of 2 pm- 3 pm and 4 pm- 5 pm. The atmospheric variables (temperature, wind speed, pressure and humidity) are used to determine the onset of a cold pool using meteorological tower data. It is interesting to note that we have observed cold pools with heavy rainfall and cold pool events with drastic changes in all these parameters but no rainfall. Wind profiler data shall provide a better understanding of these cold pools.
How to cite: Gogoi, D. and Rao, T. N.: Response of the atmospheric boundary layer to cold pools of thunderstorms at rural location, Gadanki, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-791, https://doi.org/10.5194/egusphere-egu23-791, 2023.
Abstract
This study presents a soiling forecasting (SF) tool developed by the University of Patras in order to predict the deposition of dust on Parabolic Trough Collector (PTC) mirrors. The SF estimation is occurred from the ADTM models. Dust accumulation from sedimentation, Brownian motion and impaction are considered in the estimation of deposition velocity. Moreover, the impact of rainfall is also considered. The computational procedure was divided into the laminar flow regime and the turbulence flow regime in order to estimate the rate at which dust particles can accumulate on the surface of a PTC mirror.
The meteorological data used in the model's training were taken from a weather station at the company KEAN Soft Drinks Ltd. in Limassol, Cyprus (PTC location), and the particle concentrations were obtained from CAMS global atmospheric forecasts [1]. Two variants of the model were used. The first model uses PM2.5 and PM10 (kg/m3). The second model uses a wider distribution of aerosols. Specifically, dust aerosol mixing ratio in the bins 0.03-0.55 μm, 0.55-0.9 μm and 0.9-20 μm were used.
The reflectivity estimations from both models were compared with the available PTC mirror reflectivity measurements to confirm the effectiveness of the SF tool [2]. The validation measurement campaign was conducted from June 3rd to June 7th, 2019. A major soiling event occurs within the first three days which increases gradually until June 5th and then recedes. For the chosen validation period, both models accurately captured the phasing and magnitude of reflectivity. Figure 1 illustrates the soiling mechanisms for the first model and the Figure 2 for the second model respectively. The wind speed during the 4-day period was below 6.8 m/s (laminar flow threshold). The larger particles included in the second model and the corresponding deposition velocity of the coarse particles resulted at higher values for Sedimentation and Brownian motion while Impaction had the same range between the two models (because the wind is the dominant factor of this mechanism). Therefore, the coarser particles resulted in increased influence of sedimentation over impaction in model 2. In both models, the impact of Brownian deposition was the least among the mechanisms. Moreover, the sedimentation had the highest influence, at most hours, in the modelled deposition velocity with occasional outbursts of impaction. The process of calibrating the models with data covering various atmospheric conditions is ongoing.
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Fig. 1: Input data, soiling mechanisms and reflectivity for model 1. |
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Fig. 2: Input data, soiling mechanisms and reflectivity for model 2. |
Acknowledgements
Smart Solar System (S3) project is supported under the umbrella of SOLAR-ERA.NET Cofund by Projektträger Jülich – Forschungszentrum Jülich GmbH – Energie-Technologie-Nachhaltigkeit (ETN 1) and General Secretariat of Research and Innovation (GSRI). SOLAR-ERA.NET is supported by the European Commission within the EU Framework Programme for Research and Innovation HORIZON 2020 (Cofund ERA-NET Action, N° 691664).
References
[1] CAMS, https://atmosphere.copernicus.eu
[2] P. K. Ktistis, R. A. Agathokleous, and S. A. Kalogirou, “Experimental performance of a parabolic trough collector system for an industrial process heat application,” Energy, doi: 10.1016/j.energy.2020.119288.
How to cite: Voukelatos, A., Anastasiou, A., Sattler, J. C., Alexopoulos, S., Dutta, S., and Kioutsioukis, I.: A comparison of two approaches of dust deposition for Parabolic Trough Collector Mirrors , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-16002, https://doi.org/10.5194/egusphere-egu23-16002, 2023.
