AS2.3

Air-Land Interactions (General Session)

The session is addressed to experimentalists and modellers working on land surface interactions from local to regional scales. The programme is open to a wide range of new studies in micrometeorology and related atmospheric and remote sensing disciplines. The topics include the development of new devices, measurement techniques, experimental design, data analysis methods, as well as novel findings on surface layer theory and parametrization, including local and non-local processes. The theoretical parts encompass soil-vegetation-atmosphere transport, internal boundary-layer theories and flux footprint analyses. Of special interest are synergistic studies employing experimental data, parametrizations and models. This includes energy and trace gas fluxes (inert and reactive) as well as water, carbon dioxide and other GHG fluxes. Specific focus is given to outstanding problems in land surface boundary layer descriptions such as complex terrain, effects of horizontal heterogeneity on sub-meso-scale transport processes, energy balance closure, stable stratification and night time fluxes, dynamic interactions with atmosphere, plants (in canopy and above canopy) and soils.

solicited authors:
Co-organized by SSS11, co-sponsored by iLEAPS and ICOS
Convener: Christoph Thomas | Co-conveners: Natascha Kljun, Matthias Mauder, Andreas Ibrom
vPICO presentations
| Thu, 29 Apr, 09:00–11:45 (CEST)

vPICO presentations: Thu, 29 Apr

Chairpersons: Christoph Thomas, Natascha Kljun
09:00–09:02
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EGU21-3994
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ECS
Olli Peltola, Mika Aurela, Pasi Kolari, Ivan Mammarella, Dario Papale, Timo Vesala, and Tuomas Laurila

Global eddy-covariance (EC) flux measurement networks have provided invaluable insights into ecosystem-atmosphere exchanges of gases, energy and momentum. However, EC technique underestimates surface fluxes during periods when the turbulent flow is decoupled from the surface and this deficiency casts a shade on the validity of EC flux networks. The decoupling can happen for instance when strongly stably stratified air layers or thick forest canopies inhibit vertical mixing. These so-called decoupling periods are typically identified using friction-velocity (u*) and periods when u* is below a site-specific threshold are removed from EC flux time series. This approach has at least two weaknesses: 1) it relies on uncertain site-specific threshold values and 2) it does not consider changes in processes hindering the flow coupling to the surface. Furthermore, it can be questioned whether u* is a correct metric for the strength of turbulent mixing. In this study we utilize recently proposed method which overcomes the above-mentioned weaknesses of u* filtering. The method is based on a comparison between vertical wind speed standard deviation and work done against forces (buoyancy and canopy drag) hindering the movement of a downward propagating air parcel. Via this comparison the need for site-specific thresholds is in theory alleviated. We utilize data from various contrasting EC sites to 1) evaluate whether the new method is free from site-specific thresholds also in practice, 2) compare the flux filtering methods in different conditions and 3) assess the effect of these methods on ecosystem respiration, gross primary productivity and carbon (C) balance estimates. These results will help to assess the robustness of ecosystem C flux estimates made in the past with EC and give clues on how to move forward with EC measurements during the decoupled periods.

How to cite: Peltola, O., Aurela, M., Kolari, P., Mammarella, I., Papale, D., Vesala, T., and Laurila, T.: Beyond friction-velocity thresholds: a new look on eddy-covariance flux filtering and impact on ecosystem C flux estimates, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3994, https://doi.org/10.5194/egusphere-egu21-3994, 2021.

09:02–09:04
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EGU21-3341
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ECS
Manuel Mohr, Thomas Laemmel, Martin Maier, Sven Kolbe, Christopher Jung, Matthias Zeeman, Bernard Longdoz, Alexander Knohl, Christoph Thomas, and Dirk Schindler

Previous studies showed at a forest site, that small air pressure fluctuations that are generated during periods of high wind speed significantly enhance topsoil gas transport, which is called pressure-pumping. The strength of these air pressure fluctuations can be described by the pressure pumping coefficient (PPC) which is defined as the mean absolute slope between two measurements (0.5 s) per 30 min interval. It was shown that at this site a quadratic relationship exists between the PPC and above canopy wind speed.

To investigate the variability of small air pressure fluctuations, high-frequency airflow and air pressure measurements were carried out at ten European and American sites with different land use (grassland, crop, forest, urban). The air pressure fluctuations were generally measured above the soil surface and airflow above the site-specific canopy (above trees in forests, on the top of a high building in the city). The measurements took place between 2016 and 2020 and commonly lasted at least one month per site.

Results show that the site-specific PPC increases in a quadratic relationship with above-canopy wind speed at all sites. The data was very close to a quadratic relationship at sites with rather uniform forests and level topography (R² > 0.92), while more complex sites revealed a larger scattering of this correlation (R² > 0.65).

At some sites, the PPC is also highly dependent on the prevailing wind direction. It is shown that the local surface roughness of the plant canopy can be excluded as a main driver of the PPC. Moreover, analysis of surface roughness parameters suggests that the topographic exposure around the measurement sites is responsible for the variability in the PPC.

However, due to the limited data availability and the complexity of the sites (topography, canopy, buildings), it cannot yet be ruled out that other effects have an influence on the PPC. In any case, from the results it can be inferred that wind-induced air pressure fluctuations responsible for pressure-pumping are detectable over a variety of natural and artificial surfaces. It must, therefore, be assumed that they have the potential to increase the diffusion-limited transport rate of trace gases in the soil as well as the soil-atmosphere exchange of trace gases over a large number of surfaces during periods of high wind speed.

How to cite: Mohr, M., Laemmel, T., Maier, M., Kolbe, S., Jung, C., Zeeman, M., Longdoz, B., Knohl, A., Thomas, C., and Schindler, D.: Comparison of wind-induced air pressure fluctuations at sites with different land use, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3341, https://doi.org/10.5194/egusphere-egu21-3341, 2021.

09:04–09:06
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EGU21-8527
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ECS
Jonathan D. Muller, Eyal Rotenberg, Fyodor Tatarinov, Itay Oz, and Dan Yakir

The reduced availability of evaporative cooling resulting from a hotter and drier climate can lead to high leaf temperatures resulting in overheating. This can affect a variety of biophysical and biochemical processes that could enhance mortality. Plant resilience to these increasingly stressful conditions could rely on non-evaporative cooling. However, to what extent this plays a role is poorly known at present.

In order to assess heat dissipation under the long summer drought conditions, we measured leaf-to-air temperature differences ΔTleaf-air of pine needles in semi-arid conditions in a drought-exposed and in an experimentally irrigated plot. For this purpose, we developed a novel, high accuracy system based on an infrared camera capable of continuous measurements of leaf temperature under field conditions. Both drought-exposed and irrigated trees, which had a 10x higher transpiration rate, exhibited a similar ΔTleaf-air that remained mostly below 3.5°C. Variations in mean wind speed did not strongly affect ΔTleaf-air, but it depended highly on within-canopy turbulence. This suggests a non-evaporative cooling mechanism that relies on the low leaf resistance to heat transfer, thus generating a large sensible heat flux. The ~30% reduction in resistance between leaves of drought-exposed and irrigated trees in the same species must be a result of changes in leaf characteristics and differences in canopy structure influencing wind penetration into the canopy. This reduction in resistance is required to generate the sufficiently larger sensible heat flux of nearly 100 W m-2 observed between both treatments under high radiation.

Non-evaporative cooling was demonstrated to be an effective leaf- and leaf-branch-scale cooling mechanism in trees with small leaves, which can be a critical factor in forest resistance to drying climates. The generation of a leaf-scale sensible heat flux is considered as a possible mechanism leading to the development of the previously identified canopy-scale ‘convector effect’.

How to cite: Muller, J. D., Rotenberg, E., Tatarinov, F., Oz, I., and Yakir, D.: Evidence for efficient non-evaporative leaf cooling mechanism in a pine forest under drought conditions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8527, https://doi.org/10.5194/egusphere-egu21-8527, 2021.

09:06–09:08
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EGU21-15680
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ECS
Astrid Vatne, Lena M. Tallaksen, Norbert Pirk, Ane V. Vollsnes, Kolbjørn Engeland, Poul Larsen, and Andreas Ibrom

Evapotranspiration links the energy, water and carbon budgets of wetlands, a key ecosystem in high latitudes. While the evapotranspiration in high latitude wetlands is largely controlled by available energy, the surface also exerts a non-negligible control. The surface control on evapotranspiration, often represented by the surface conductance, is sensitive to environmental variables such as vapour pressure deficit (VPD). Previous studies have shown that higher surface conductance leads to higher evapotranspiration from high latitude wetlands than from high latitude forests during periods of high VDP. However, it is unclear how the surface conductance-VPD relation varies across climatic gradients. To study the sensitivity of surface conductance to increasing values of VPD, we use data from three recently established eddy covariance sites in Norway, situated along high latitude climatic gradients. The sites included are Hisåsen (680 m.a.s.l., N 61.11°, E 12.24°), Finse (1200 m.a.s.l., N 60.59°, E 7.53°) and Iškoras (360 m.a.s.l, N 69.34°, E 25.29°). We first estimate surface conductance from the eddy covariance data, by inverting the Penman-Monteith equation. We then apply a boundary line analysis to assess the sensitivity of the surface conductance to VPD. Our preliminary results show a lower sensitivity of surface conductance to VPD on the northernmost site, compared to the two sites at lower latitude. Further work is needed to relate the observed variations in surface conductance-VPD relation to surface characteristic, and we hypothesize that the observered lower sensitivity in surface conductance is related to lower values of leaf area index. This work is a contribution to the Strategic Research Initiative ‘Land Atmosphere Interaction in Cold Environments’ (LATICE) of the University of Oslo.

How to cite: Vatne, A., Tallaksen, L. M., Pirk, N., Vollsnes, A. V., Engeland, K., Larsen, P., and Ibrom, A.: Sensitivity of evapotranspiration and surface conductance to vapour pressure deficit across high latitude climatic gradients., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15680, https://doi.org/10.5194/egusphere-egu21-15680, 2021.

09:08–09:10
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EGU21-15000
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ECS
Stefanie Falk, Ane Victoria Vollsnes, Lisa Emberson, Connie O'Neill, Aud Else Berglen Eriksen, Frode Stordal, and Terje Koren Berntsen

An increased occurrence of persistent heatwaves, as one possible future scenario, generates favorable conditions for the formation of ambient air ozone. Vegetation highly specialized to sub-arctic climate is vulnerable to rapid environmental changes inflicted by global warming and might become more susceptible to ozone in the future. Over large parts of Europe the summer 2018 had been extraordinarily hot and dry and caused large wildfires in northern Sweden in particular. This can be regarded as a test case for such a future scenario. In both 2018 and 2019, we have monitored ambient air ozone concentrations at the Norwegian Institute of Bioeconomy Research (NIBIO) Environment Centre Svanhovd in Northern Norway. Due to
data acquisition problems, ozone concentrations for two weeks in July 2018 were missing from our record. We present a reconstruction based on probability density function with respect to the Swedish and Finnish atmospheric monitoring sites in the region. Over all, ozone concentrations did not differ significantly between the two years. While temperatures and global irradiance diverged significantly from multi annual mean, precipitation varied only to some extend. Coincidentally, we have observed ozone-induced visible injuries on clovers in the ozone garden at Svanhovd in 2018, but not in 2019. We investigate the difference in uptake of ozone using the DO3SE model, with respect to the typical vegetation (e.g., birch and conifers) at
the location. We assess whether critical levels on POD1 for these species were breached. We find that an unadjusted transfer of currently used standard parameters and methodes on ozone damage assessment (IPC Mapping Manual) to vegetation in the subarctics will result in an missinterpretation of POD1 values.

How to cite: Falk, S., Vollsnes, A. V., Emberson, L., O'Neill, C., Berglen Eriksen, A. E., Stordal, F., and Koren Berntsen, T.: The 2018 heatwave and its implications on ozone induced damage on vegetation in a subarctic climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15000, https://doi.org/10.5194/egusphere-egu21-15000, 2021.

09:10–09:12
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EGU21-8919
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ECS
Ladislav Šigut, Thomas Wutzler, Tarek El-Madany, Milan Fischer, and Mirco Migliavacca

Our understanding of the carbon and water cycle was greatly improved through application of eddy covariance measurements in recent decades. Though powerful, this micrometeorological approach relies on a number of assumptions that can be affected by a selection of station location. Most importantly, terrain of the target area should be flat, target area should be homogeneous and adequate air mixing should be achieved. Although possible shortcomings can be reduced by careful site inspection before tower installation (flat terrain) or can be corrected for during data post-processing (filtering of periods with low mixing), preliminary assessment of target area homogeneity is difficult as well as correction of its impacts afterwards. The influence of such inhomogeneities can lead to a bias in the flux annual sums but also a bias in their relationships with environmental variables. Certain solutions were already proposed, but target area homogeneity was so far assessed only at a few selected sites. Here we aim to provide a suit of software tools that build on the existing software packages (REddyProc, Flux Footprint Prediction, openair, openeddy) and allow easy diagnosis of the situation at the given ecosystem station. We plan to provide directional analyses of variables of interest. This will allow to identify the wind sectors that show large deviations from the mean value of the whole target area. In a further step, we plan to combine footprint modeling with CO2 and energy flux measurements and thus provide attribution of mean (weighted) fluxes to their source area. Based on the differences with the directional analyses we will assess whether the higher computational expenses of footprint modeling are justified and bring additional information. Finally, we plan to separate the target area to a limited amount of wind sectors and attempt separate gap-filling and flux partitioning for areas identified by preceding homogeneity evaluation. The limitations and feasibility of this approach will be assessed.

This work was supported by the Ministry of Education, Youth and Sports of CR within Mobility CzechGlobe2 (CZ.02.2.69/0.0/0.0/18_053/0016924).

How to cite: Šigut, L., Wutzler, T., El-Madany, T., Fischer, M., and Migliavacca, M.: A tool for evaluation of target area homogeneity at ecosystem stations employing eddy covariance method, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8919, https://doi.org/10.5194/egusphere-egu21-8919, 2021.

09:12–09:14
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EGU21-414
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ECS
Theresia Yazbeck, Gil Bohrer, Chante' Vines, Frederik De Roo, Matthias Mauder, and Bhavik Bakshi

Trees have a large role in improving urban air quality, among other mechanisms, through dry deposition of scalars and aerosols on leaf surfaces. We tested the role of leaf density and canopy structure in modulating the rate of dry deposition. We simulated the interactions between a virtual forest patch and deposition rate of an arbitrary scalar using the Parallelized Large Eddy Simulation Model (PALM). Two canopy structures were considered: a homogenous canopy; and canopy stripes perpendicular to the wind direction. For each canopy stripe scenario, we considered thin, intermediate, and wide stripes, while the space between stripes equals the stripes’ width. Four leaf area densities were considered for each case. The results showed that stripes perpendicular to the wind direction had a larger deposition per leaf area than homogeneous canopies, and denser canopies had more total deposition, but lower per-leaf area rate. Our results can be explained by canopy-induced turbulence structures that couple the air within and above the canopy and lead to more effective leaf area where this coupling is stronger. We aggregate our results to the whole-patch scale and suggest a canopy-structure and leaf-area dependent correction to the canopy resistance parameter so to be used in coarse models that resolve dry deposition. 

How to cite: Yazbeck, T., Bohrer, G., Vines, C., De Roo, F., Mauder, M., and Bakshi, B.: Effects of spatial heterogeneity of leaf density and crown spacing of canopy patches on dry deposition rates, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-414, https://doi.org/10.5194/egusphere-egu21-414, 2021.

09:14–09:16
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EGU21-15722
Maarten van Reeuwijk and Tom Grylls

Trees play an important role in the urban heat island effect and urban air quality due to their impact on the transfer of radiation, momentum, heat, moisture and pollution. However, the effects of trees are hard to quantify due to their complex interactions with urban surfaces and the turbulent atmosphere overhead.

We present a complete tree model for large-eddy simulations (LES) that represents the effects of trees on drag, transpiration, shading and deposition at resolutions of O(1 m, 0.1 s) whilst minimising the number of model parameters. The tree model avoids the necessity to resolve the leaf temperature via a derivation of the Penman-Monteith equation and distinguishes between cooling via transpiration and shading. The latent heat flux is further broken down into radiative and advective components in order to better understand the mechanism behind transpirational cooling (e.g. the ‘oasis’ effect).

The new tree model is investigated analytically to provide insight into tree cooling regimes, and is applied to field studies to contextualise the analysis. The combined cooling effect of trees due to transpiration and shading processes can be reduced to a four-dimensional parameter space. The net tree cooling (NTC) and tree cooling ratio (TCR) parameters are defined to enable a systematic categorisation of the thermal effect of a tree into five regimes: net heating, net reduction (shading dominated), net reduction (transpiration dominated), net cooling (shading dominated) and net cooling (transpiration dominated). Existing parameterisations for tree cooling are reviewed, illustrating their limitations and highlighting the need for complete models to determine tree cooling.

The tree model is implemented into the LES model uDALES. The drag and canopy energy balance models are validated, and results are presented for domains that are 1) fully covered by trees; 2) partially covered by trees; and 3) have a single line of trees. These simulations provide physical insight into the effect of trees on the microclimate and provide evaluation data for future studies.

How to cite: van Reeuwijk, M. and Grylls, T.: Tree model with drag, transpiration, shading and deposition: Identification of cooling regimes and large-eddy simulation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15722, https://doi.org/10.5194/egusphere-egu21-15722, 2021.

09:16–09:18
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EGU21-12396
Ebba Dellwik, Poul Hummelshøj, and Gerhard Peters

Sonic anemometers provide point observations of the three-dimensional velocity field at high sampling rates and are crucial instruments for understanding and quantifying the fluxes of momentum, energy and scalars between the atmosphere and Earth’s surface. Since the beginning of sonic anemometry 50 years ago, the characterization of flow distortion, i.e. how the instrument structure alters the flow, has been an ongoing research topic. Multi-path sonic anemometry provides a new opportunity to research and understand flow distortion on the vertical velocity component, since several positions in the small measurement volume can be measured simultaneously. In this work, we use data from a flat terrain measurement campaign in 2020, in which several sonic anemometers were mounted on 4m towers placed 4m apart. The analysis is focused on the Multipath Class-A sonic anemometer (Metek GmbH, Germany), which provides vertical velocity observations from three vertical paths 120 degrees and 0.1m apart. Vertical velocities are also calculated from several combinations of the tilted paths. We investigate how the vertical velocity component is altered depending on wind direction relative to different parts of the instrument structure. We demonstrate that by an optimal combination of the different paths, the vertical velocity variance and fluxes can be significantly enhanced. We also show spectra, and especially look at the high frequency end of the spectrum, where the relative behaviour of the velocity components is known from fundamental turbulence theory. Further, the relative importance of transducer shadowing and pressure-induced blockage effects is discussed.

How to cite: Dellwik, E., Hummelshøj, P., and Peters, G.: An analysis of  flow distortion in a multipath sonic anemometer, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12396, https://doi.org/10.5194/egusphere-egu21-12396, 2021.

09:18–09:20
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EGU21-14464
Ivan Mammarella, Olli Peltola, Toprak Aslan, Andreas Ibrom, Eiko Nemitz, and Üllar Rannik

Eddy covariance (EC) scalar flux loss at high frequency is due to the incapability of the measurement system to detect small-scale variation of atmospheric turbulent signals. This systematic bias is particularly important for closed-path systems, and it is mainly related to inadequate sensor frequency response, sensor separation and the air sampling trough tubes and filters. Here, we investigate the limitations of current approaches, based on measured power spectra (PSA) or cospectra (CSA), to empirically estimated the spectral transfer function of the EC system needed for the frequency response correction of measured fluxes. We performed a systematic analysis by using EC data from a wetland and forest site for a wide range of attenuation levels and signal-to-noise ratio. We proposed a novel approach for PSA that uses simultaneously the noise and the turbulent signals present in the power spectrum, providing robust estimates of spectral transfer function for all conditions. We further theoretically derived a new transfer function to be used in the CSA approach which specifically accounts for the interaction between the low-pass filtering induced phase shift and the high frequency attenuation. We show that current CSA approaches neglect such effect, giving a non-negligible systematic bias to the estimated scalar fluxes from the studied sites. Based on these findings, we recommend that spectral correction methods, implemented in EC data processing algorithms, are revised accordingly.

How to cite: Mammarella, I., Peltola, O., Aslan, T., Ibrom, A., Nemitz, E., and Rannik, Ü.: Revising the high frequency response correction of scalar fluxes measured by closed-path eddy covariance systems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14464, https://doi.org/10.5194/egusphere-egu21-14464, 2021.

09:20–09:22
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EGU21-2181
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ECS
Justus van Ramshorst, Christian Markwitz, Timothy Hill, Robert Clement, Alexander Knohl, and Lukas Siebicke

Agroforestry is an integration of trees in cropland or grassland and is discussed, within Germany and the EU, as a potential “Green Solution” for agriculture. Agroforestry alters the microclimate, productivity, biodiversity, and nutrient and water usage – as compared to standard agricultural practise. A potentially key benefit is the higher carbon sequestration of agroforestry, relative to monoculture systems, which could provide an interesting option for mitigating climate change, while still providing valuable arable land. Net ecosystem exchange studies of CO2 (NEE) of agroforestry systems are rare, in comparison to the extensive studies of NEE of agricultural systems (croplands and grasslands). Therefore, the current study, as part of the SIGNAL (sustainable intensification of agriculture through agroforestry) project, investigates the NEE of agroforestry compared to that of monoculture agriculture.

At five locations across Germany, paired flux measurements above agroforestry and monoculture agronomy are performed using innovative low-cost CO2 eddy covariance sensors (slow response Vaisala GMP343 IRGA, with custom made housing). During the summer of 2020 simultaneous measurements of the low-cost setup and a LI-COR 7200 are performed, above grassland at 3.5 m and adjacent agroforestry grassland at 10 m measurements height.

The low-cost eddy covariance system is able to capture the turbulent (diurnal) CO2 flux dynamics and the response to management activities. After spectral corrections and applying quality control, the low-cost system at the agroforestry site (slope = 0.92, R2 = 0.88) performs better than the low-cost system at the grassland site (slope = 0.67, R2 = 0.80), when compared to the LI-COR measurements. This is probably due to the difference in turbulence caused by different surface roughness and measurement height. The preliminary cumulative carbon flux during the four-month measurement campaign shows a significant difference between the grassland (source of (+) 16-38 gC/m2) and agroforestry grassland (sink of (-) 148-164 gC/m2), in favour of agroforestry. By applying post processing software, we aim to further optimize the frequency corrections for the low-cost system. In the future the obtained post processing scheme will be applied to the other low-cost eddy covariance systems within the project.

How to cite: van Ramshorst, J., Markwitz, C., Hill, T., Clement, R., Knohl, A., and Siebicke, L.: Evaluation of low-cost eddy covariance for CO2 fluxes over agroforestry and grassland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2181, https://doi.org/10.5194/egusphere-egu21-2181, 2021.

09:22–09:24
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EGU21-13548
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ECS
Tyler Waterman, Gabriel Katul, Andy Bragg, and Nathaniel Chaney

The implementation of higher-order turbulence closure schemes in Earth system models (e.g., the Cloud Layers Unified by Binormals; CLUBB) aims to improve the modeling of convection and radiative transfer in numerical weather prediction and climate models. However, the added value of these schemes is constrained by the specification of boundary conditions on higher-order statistics. At the land surface, many of the higher order turbulence statistics that are required as boundary conditions are parameterized using formulations more appropriate for stationary and planar-homogeneous flow in the absence of subsidence. A case in point is the variance of the potential temperature fluctuations.  Because of the additive nature of variances arising from non-uniformity in surface heating, current parameterizations are not readily generalizable. The current scheme used in CLUBB, as well as other models, relies on limited studies over uniform terrain, with the variance entirely determined by local sensible heat flux, friction velocity, and the Obukhov stability parameter without regard to local site characteristics. This presentation aims to address this weakness by leveraging the National Ecological Observation Network (NEON) network of eddy covariance towers to validate the current parameterization scheme for potential temperature variance, as well as propose improvements for more heterogeneous terrain.

The turbulence fluctuations of temperature at 39 NEON sites are processed and quality controlled, removing points occurring at night, while precipitation is falling, and with sub-zero temperatures. Results overall indicate the current scheme performs well, especially over flat homogeneous terrain where local flux relationships dominate. When there is sufficiently heterogeneous, rough terrain or non-closure of the local energy balance, however, existing schemes fail to accurately estimate the variances in temperature. In these cases, the parameterization needs to be modified, and initial results suggest simple adjustments can yield improvements and reduce error close to that of the uniform sites with local energy balance closure. The successful improvement of the temperature variance parameterization scheme implies high potential for similar, new, empirically derived parameterizations for the surface boundaries for other higher order turbulent statistics (e.g. temperature skewness) in atmospheric turbulence models.

How to cite: Waterman, T., Katul, G., Bragg, A., and Chaney, N.: Evaluating and Improving Parameterizations of the Variance of Temperature Fluctuations Over Heterogeneous Landscapes for Surface Boundary Conditions in Atmospheric Models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13548, https://doi.org/10.5194/egusphere-egu21-13548, 2021.

09:24–09:26
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EGU21-7576
Volker Wulfmeyer and David D. Turner

The Land-Atmosphere Feedback Experiment (LAFE) deployed several state-of-the-art scanning lidar and remote sensing systems to the Atmospheric Radiation Measurement (ARM) Program Southern Great Plains (SPG) site during August 2017. A novel synergy of remote sensing systems was applied for simultaneous measurements of land-surface fluxes and horizontal and vertical transport processes in the atmospheric boundary layer (ABL). The impact of spatial inhomogeneities of the soil-vegetation continuum on L-A feedback was studied using the scanning capability of the instrumentation as well as soil, vegetation, and surface flux measurements. Thus, both the variability of surface fluxes and ABL dynamics and thermodynamics over the SGP site was studied for the first time. The objectives of LAFE are as follows:

I. Determine turbulence profiles and investigate new relationships among  gradients, variances, and fluxes
II. Map surface momentum, sensible heat, and latent heat fluxes using a synergy of scanning wind, humidity, and temperature lidar systems
III. Characterize land-atmosphere feedback and the moisture budget at the SGP site via the new LAFE sensor synergy
IV: Verify large-eddy simulation model runs and improve turbulence representations in mesoscale models.

In this presentation, the status of LAFE research and recent achievements of the science objectives are presented and discussed. Concerning I., long-term profiling capabilities of turbulent properties have been developed and will be presented such as continuous measurements of latent heat flux profiles for a duration of one month. Concerning II., we present a combination of tower and remote sensing measurements to study surface layer profiles of wind, temperature, and humidity. A first evaluation of the results demonstrates significant deviations from Monin-Obukhov similarity theory. Concerning III., Convective Triggering Potential (CTP)-Humidity Index (HIlow) metrics are presented at the SGP site to characterize L-A feedback and a new technique for determination of water-vapor advection, as important part of its budget. Last but not least, concerning IV., we present an advanced ensemble model design with turbulence permitting resolution for case studies and model verification from the convection-permitting to the turbulent scales in a realistic mesoscale environment. Using this framework, we introduce a strategy to apply the observations for the test and development of turbulence parameterizations. These results confirm that LAFE will make significant contributions to process understanding and the parameterization of the next generation of high-resolution weather forecast, climate, and earth system models.

How to cite: Wulfmeyer, V. and Turner, D. D.: New results of the Land Atmosphere Feedback Experiment (LAFE), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7576, https://doi.org/10.5194/egusphere-egu21-7576, 2021.

09:26–10:30
Break
Chairpersons: Andreas Ibrom, Matthias Mauder
11:00–11:02
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EGU21-7693
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ECS
Florian Späth, Shehan Morandage, Andreas Behrendt, Thilo Streck, and Volker Wulfmeyer

A new Land-Atmosphere Feedback Observatory (LAFO) was established at the University of Hohenheim, Stuttgart, Germany. It is considered as a role model for a network of GEWEX LAFOs (GLAFOs) that is a central project and proposed by the GEWEX Global Land/Atmosphere System Study (GLASS) panel (Wulfmeyer et al. 2020). Its main objective is to observe directly land-atmosphere (L-A) feedback for process understanding and improving its representation in weather and climate models. The set up phase of this research facility was funded as infrastructure project of the Carl Zeiss Foundation. The main goals are to

1) investigate the diurnal cycle of the planetary boundary layer (PBL) including its turbulent properties,
2) improve parameterizations based of vegetation dynamics, surface and PBL fluxes, and
3) verify mesoscale and turbulence permitting models,
4) characterize L-A feedback by suitable metrics.

LAFO brings together a sensor synergy with unequaled spatial and temporal resolution. An extended set of soil physical, plant dynamic as well as meteorological variables throughout the PBL are measured focusing on evapotranspiration and turbulent exchange processes over an agricultural landscape. Observations are recorded with state-of-the-art instruments on a long-term basis as well as with a more sophisticated sensor setup campaign based.

The first key component of the LAFO sensor synergy consists of 3D scanning lidar systems: A scanning water vapor differential absorption lidar and a scanning temperature and humidity rotational Raman lidar, both developed at the Institute of Physics and Meteorology. Both systems are worldwide unique and provide water vapor and temperature remote sensing data in the surface layer up to the lower free troposphere with very high resolution up to the turbulent scale (Behrendt et al. 2015, Wulfmeyer et al. 2015, Muppa et al. 2016, Späth et al. 2016, Lange et al. 2019). Additionally, two scanning Doppler lidars measure the horizontal and vertical wind profiles and turbulent wind fluctuations. The lidar measurements are complemented by a 3D scanning Doppler cloud radar.

The second key component is a soil water and soil temperature sensor network distributed over the agricultural study area combined with two eddy-covariance stations (Imukova et al. 2016) to observe fluxes at the land surface.

The third key component consists of devices for vegetation characterization. As an example, the “BreedVision” phenotyping platform (Busemeyer et al. 2013) based on an innovative sensor-setup provides an extensive set of sensor-data for field phenotyping and feature prediction without vegetation destruction. Unman aerial vehicles (UAVs) with spectroscopic cameras are also available.

For specific campaigns studying L-A feedback with particularly high detail, research partners are highly welcome to join our research team. Following the FAIR (Findable, Accessible, Interoperable, Reusable) data principle, our data will be made available on a website. We present first measurement examples and show how these can be used to reach our research goals.

 

Wulfmeyer et al. 2020, GEWEX Quarterly Vol. 30, No. 1.
Behrendt et al. 2015, doi:10.5194/acp-15-5485-2015
Wulfmeyer et al. 2015, doi:10.1002/2014RG000476
Muppa et al. 2016, doi:10.1007/s10546-015-0078-9
Späth et al. 2016, doi:10.5194/amt-9-1701-2016
Lange et al. 2019, doi:10.1029/2019GL085774
Imukova et al. 2016, doi:10.5194/bg-13-63-2016
Busemeyer et al. 2013, doi:10.3390/s130302830

How to cite: Späth, F., Morandage, S., Behrendt, A., Streck, T., and Wulfmeyer, V.: The Land-Atmosphere Feedback Observatory (LAFO), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7693, https://doi.org/10.5194/egusphere-egu21-7693, 2021.

11:02–11:04
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EGU21-12968
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ECS
Johannes Speidel, Hannes Vogelmann, Matthias Perfahl, Matthias Mauder, and Luise Wanner

Connecting the earth's surface with the free troposphere, the planetary boundary layer (PBL) comprises complex dynamics of turbulent behavior. This especially applies for areas with heterogeneous terrain. Relevant near-ground processes such as released energy fluxes and the emission of aerosols and trace gases directly interact with the atmosphere. Therefore, the PBL's physical state is determined both by the near-ground processes as well as entrainment of air parcels from higher layers. The mainly turbulence-driven transport of particles and properties throughout the PBL constrain a comprehensive understanding of the PBL's behavior. Hence, the energy balance closure problem as well as errors in precipitation forecast in long-term numerical weather predictions, amongst others, remain unresolved challenges. Here, ground-based lidar profiling is a well suitable method for observing the PBL, as data sampling allows for high temporal and vertical resolutions (Here: Sampling rate of 100\,Hz and 7.5\,m). During the CHEESEHEAD campaign, carried out in summer 2019, our newly developed ATMONSYS lidar performed measurements over complex terrain in northern Wisconsin. There, our lidar system was embedded in a dense network of multiple in-situ and remote sensing instruments. The central aim of this campaign was to further contribute to solve the energy balance closure problem. With the ATMONSYS lidar, vertical columns of aerosol backscatter coefficients, water vapor and temperature have been recorded. The presented work shows what the data is suitable for in terms of resolution and temporal extent in the first place. As a second point, focus is given on structure and variability of aerosol backscatter coefficient distributions and water vapor concentrations as well as their implications on the prevailing state of the PBL. Based on the presented findings, we discuss the potential and suitability of this experimental data for deriving transport processes within the PBL.

How to cite: Speidel, J., Vogelmann, H., Perfahl, M., Mauder, M., and Wanner, L.: Ground-based lidar observations of vertical aersosol and water vapor profiles within the boundary layer over heterogeneous terrain, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12968, https://doi.org/10.5194/egusphere-egu21-12968, 2021.

11:04–11:06
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EGU21-563
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ECS
Luigi Brogno, Francesco Barbano, Laura Sandra Leo, Harindra Joseph Fernando, and Silvana Di Sabatino

Low-level jets (LLJs) are a peculiar feature of the nocturnal Planetary Boundary Layer (PBL) and they have been extensively observed both in flat and complex terrain configurations. On the contrary, double-nosed LLJs have been rarely investigated. They essentially consist in the simultaneous occurrence of two noses (i.e. two wind-speed maxima) within the PBL vertical profile of wind speed, but their origin and mechanisms remain rather unclear.

Data collected in an open valley during the MATERHORN field experiment are used here first to demonstrate that double-nosed LLJs are frequently observed at the site during stable nocturnal conditions, and second to describe the mechanisms that drive their formation. Structural characteristics of these double-nosed LLJs are originally described using refined criteria proposed in the literature.

Two driving mechanisms for double-nosed LLJs are newly proposed in the current study. The first mechanism is wind-driven, in which the two noses are associated with different air masses flowing one on top of the other. The second mechanism is wave-driven, in which a flow perturbation generates an inertial-gravity wave. This wave vertically transports momentum causing the occurrence of a secondary nose, leading to the formation of a double-nosed LLJ. Careful examination of the temporal evolution of these events also revealed the short-lived and transitional nature of the secondary nose in both the mechanisms, as opposite to the primary nose whose evolution appeared instead driven by inertial oscillations. Application of two analytical inertial-oscillation models retrieved from the literature confirms this hypothesis. Indeed, both models satisfactorily reproduce the observed single-nosed LLJs but fail to capture the temporary formation of the secondary nose.

How to cite: Brogno, L., Barbano, F., Leo, L. S., Fernando, H. J., and Di Sabatino, S.: Double-Nosed Low-Level Jets over Complex Terrain: Driving Mechanisms and Analytical Modeling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-563, https://doi.org/10.5194/egusphere-egu21-563, 2021.

11:06–11:08
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EGU21-13379
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ECS
Jason Simon, Tyler Waterman, Finley Hay-Chapman, Paul Dirmeyer, Andrew Bragg, and Nathaniel Chaney

Land-surface heterogeneity is known to play an important role in land-surface hydrology, which drives the bottom boundary condition for atmospheric models in numerical weather prediction (NWP) applications. However, the ultimate impact of land-surface heterogeneity on atmospheric boundary layer (ABL) development is still an open problem with implications for sub-grid scale (SGS) parameterizations for both NWP and climate modeling. Large-eddy simulation (LES) is often used to study the effects of land-surface heterogeneity on ABL development, most typically via specified surface fields which are not influenced by the atmosphere (i.e. semi-coupled). Heterogeneous land surfaces have been seen in previous studies to have a significant influence on ABL dynamics, particularly cloud production, in certain cases when semi-coupled to the atmosphere.

Here we use the Weather Research and Forecasting (WRF) model as an LES with both semi-coupled and fully-coupled land surfaces to investigate the impact of two-way coupling on the interaction between heterogeneous land surfaces and daytime ABLs. For semi-coupled simulations, the HydroBlocks land-surface model is run offline, driven by 4-km NLDAS-2 meteorology with Stage-IV radar rainfall data, and then used to specify the bottom boundary in WRF. The WRF-Hydro model is used for cases where the land surface is fully coupled to the WRF model. Both land-surface models use the Noah-MP model as their underlying physics package and add both subsurface and overland flow routing. The WRF model uses a 100-m horizontal resolution, and the land-surface models use high resolution (30 m) datasets that were upscaled to match the LES resolution for elevation, landcover, and soil type using NED, NLCD, and POLARIS respectively. These LES experiments are performed over the ARM Southern Great Plains Site atmospheric observatory in Oklahoma during the Summer of 2017 with a grid size of 100 km x 100 km to imitate a single cell in a modern climate model. The impact of land-surface heterogeneity on the atmosphere is evaluated by comparing simulations using the fully heterogeneous land surfaces with simulations where the land surface is homogenized at each timestep, taking a domain-wide spatial mean value at every grid cell. Results are evaluated primarily by the differences in the development of clouds and evolution of turbulent kinetic energy in the ABL.

How to cite: Simon, J., Waterman, T., Hay-Chapman, F., Dirmeyer, P., Bragg, A., and Chaney, N.: An Analysis of the Importance of a Fully-Coupled Atmosphere and Land-Surface When Considering the Impact of Multi-Scale Land Spatial Heterogeneity on Cloud Development, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13379, https://doi.org/10.5194/egusphere-egu21-13379, 2021.

11:08–11:10
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EGU21-11853
Rong Ma, Wei Yao, Meng Lu, and Zhitong Yu

The Flux information based on momentum, energy and matter is an important link between different components of the earth system. Flux observation is of great significance for understanding the energy and matter exchange in each circle of the earth system, revealing the carbon cycle process at the same time. Fluxes between the atmosphere and the Earth's surface must pass through the atmospheric boundary layer and have considerable influence on the state of the atmospheric boundary layer. Therefore, the observation and analysis of vertical turbulent flux in the atmospheric boundary layer has become a hot topic of atmospheric research. Based on the development of turbulence theory, the method of calculating gas-flux in the atmospheric boundary layer is constantly improved. In recent years, with the development of lidar detection system, doppler lidar system and differential absorption lidar system have also been effectively used to measure the mean wind speed and small-scale dynamic turbulence parameters, which can be applied to directly detect gas flux of the atmospheric boundary layer. For major scientific issues in the global carbon cycle and carbon emission reduction monitoring needs, this paper has developed a new method of gas-flux calculation of atmospheric boundary layer, while obtaining the wind profile information and gas concentration profile information at the same time and at the same place by the detection of lidar system. This method calculates flux takes into account the atmospheric stability judgment, surface friction velocity and the Monin-Obukhov stability parameter based on the turbulent transport theory of atmospheric boundary layer. It can quickly and effectively realize the active remote sensing detection of the gas flux information of atmospheric boundary layer under different atmospheric stability conditions,which has been proved to be effective and accurate by comparing with other gas-flux data.

How to cite: Ma, R., Yao, W., Lu, M., and Yu, Z.: A New Method for Gas-Flux Calculation in Atmospheric Boundary Layer Based on the Active Detection of LiDAR System, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11853, https://doi.org/10.5194/egusphere-egu21-11853, 2021.

11:10–11:12
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EGU21-6272
George Burba, Abby Brooke, Lauren Doggett, Kristin Feese, Jonathan Goodding, Dave Johnson, Paula Leibbrandt, Thad Miller, Kelli Rice, and Micah Witt

The Eddy Covariance method is a micrometeorological technique of high-speed measurements of water vapor, gases, heat, and momentum transport within the atmospheric boundary layer. For decades, this technique has been widely used by micrometeorologists, covering over 2100 stationary measurement locations, and numerous airborne and shipborne campaigns. Modern instrumentation and software are rapidly expanding the use of this method in many non-micrometeorological areas of scientific research, and in regulatory and commercial applications. However, a number of researchers from the disciplines outside the micrometeorology and the majority of non-academic investigators are still not familiar enough with the proper implementation of the method required for conducting high-quality, reliable, traceable, and defensible measurements in their respective areas of interest.

Although mostly automated, the method is still mathematically complex, and requires significant care to correctly design the task-specific measurement and data handling system, set up the physical site, and process and analyze the large volumes of data. Efforts of the flux networks (e.g., FluxNet, Ameriflux, Asiaflux, ICOS, NEON, OzFlux, etc.) have led to major progress in the unification of the terminology and general standardization of processing steps. The project-specific details of the methodology itself, however, are difficult to unify because various experimental sites and purposes of studies dictate different treatments, and site-, measurement- and purpose-specific approaches.

With this in mind, step-by-step instructions were created to introduce a novice to general principles, requirements, applications, processing and analysis steps of the conventional Eddy Covariance technique, and to assist in further understanding the method through more advanced references such as textbooks on micrometeorology, guidelines from the flux networks, journals, and technical papers. These are provided in the form of the free electronic resource, a 620-page textbook titled "Eddy Covariance Method for Scientific, Regulatory, and Commercial Applications". The explanations are written in a non-technical language to be of practical use to those new to this field.

Information is provided on the theory of the method (including the state of methodology, basic derivations, practical formulations, major assumptions, sources of errors, error treatments, etc.), practical workflow (e.g., experiment design, implementation, data processing, quality control, and analysis), data sharing and flux stations networking, key alternative methods, and the most frequently overlooked details.

 

References:

  • Aubinet, M., T. Vesala, and D. Papale (Eds), 2012. Eddy Covariance: A Practical Guide to Measurement and Data Analysis. Springer, 442 pp.
  • Burba, G., 2021. Eddy Covariance Method for Scientific, Regulatory, and Commercial Applications. LI-COR Biosciences, 620 pp. (under review)
  • Burba, G., 2013. Eddy Covariance Method for Scientific, Industrial, Agricultural and Regulatory Applications. LI-COR Biosciences, 331 pp.
  • Burba, G., 2021. Atmospheric Flux Measurements. In W. Chen, D. Venables, and M. Sigris (Eds.). Advances in Spectroscopic Monitoring of the Atmosphere. Elsevier, 510 pp. (in press)
  • Foken, T., 2017. Micrometeorology. Berlin: Springer, 362 pp.
  • Lee, X., 2018. Fundamentals of boundary-layer meteorology. Springer, 255 pp.
  • Lee X., W. Massman, and B. Law (Eds), 2004. Handbook of Micrometeorology: A Guide for Surface Flux Measurement and Analysis. Springer, 250 pp.
  • Monson, R. and D. Baldocchi, 2014. Terrestrial biosphere-atmosphere fluxes. Cambridge University Press, 487 pp.

How to cite: Burba, G., Brooke, A., Doggett, L., Feese, K., Goodding, J., Johnson, D., Leibbrandt, P., Miller, T., Rice, K., and Witt, M.: Using Eddy Covariance Method in Disciplines beyond Micrometeorology for Scientific, Regulatory, and Commercial Applications, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6272, https://doi.org/10.5194/egusphere-egu21-6272, 2021.

11:12–11:14
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EGU21-3962
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ECS
Gitanjali Thakur, Stan Schymanski, Kaniska Mallick, and Ivonne Trebs

The surface energy balance (SEB) is defined as the balance between incoming energy from the sun and outgoing energy from the Earth’s surface. All components of the SEB depend on land surface temperature (LST). Therefore, LST is an important state variable that controls the energy and water exchange between the Earth’s surface and the atmosphere. LST can be estimated radiometrically, based on the infrared radiance emanating from the surface. At the landscape scale, LST is derived from thermal radiation measured using  satellites.  At the plot scale, eddy covariance flux towers commonly record downwelling and upwelling longwave radiation, which can be inverted to retrieve LST  using the grey body equation :
             Rlup = εσ Ts4 + (1 − ε) R ldw         (1)
where Rlup is the upwelling longwave radiation, Rldw is the downwelling longwave radiation, ε is the surface emissivity, Ts  is the surface temperature and σ  is the Stefan-Boltzmann constant. The first term is the temperature-dependent part, while the second represents reflected longwave radiation. Since in the past downwelling longwave radiation was not measured routinely using flux towers, it is an established practice to only use upwelling longwave radiation for the retrieval of plot-scale LST, essentially neglecting the reflected part and shortening Eq. 1 to:
               Rlup = εσ Ts4                        (2)
Despite  widespread availability of downwelling longwave radiation measurements, it is still common to use the short equation (Eq. 2) for in-situ LST retrieval. This prompts the question if ignoring the downwelling longwave radiation introduces a bias in LST estimations from tower measurements. Another associated question is how to obtain the correct ε needed for in-situ LST retrievals using tower-based measurements.
The current work addresses these two important science questions using observed fluxes at eddy covariance towers for different land cover types. Additionally, uncertainty in retrieved LST and emissivity due to uncertainty in input fluxes was quantified using SOBOL-based uncertainty analysis (SALib). Using landscape-scale emissivity obtained from satellite data (MODIS), we found that the LST  obtained using the complete equation (Eq. 1) is 0.5 to 1.5 K lower than the short equation (Eq. 2). Also, plot-scale emissivity was estimated using observed sensible heat flux and surface-air temperature differences. Plot-scale emissivity obtained using the complete equation was generally between 0.8 to 0.98 while the short equation gave values between 0.9 to 0.98, for all land cover types. Despite additional input data for the complete equation, the uncertainty in plot-scale LST was not greater than if the short equation was used. Landscape-scale daytime LST obtained from satellite data (MODIS TERRA) were strongly correlated with our plot-scale estimates, but on average higher by 0.5 to 9 K, regardless of the equation used. However, for most sites, the correspondence between MODIS TERRA LST and retrieved plot-scale LST estimates increased significantly if plot-scale emissivity was used instead of the landscape-scale emissivity obtained from satellite data.

How to cite: Thakur, G., Schymanski, S., Mallick, K., and Trebs, I.: Plot-scale retrieval of land surface temperature and emissivity estimation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3962, https://doi.org/10.5194/egusphere-egu21-3962, 2021.

11:14–11:16
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EGU21-14126
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ECS
Shaofei Wang, Ji Zhou, Xiaodong Zhang, and Zichun Jin

Land surface temperature (LST) is a key factor in earth–atmosphere interactions and an important indicator for monitoring environmental changes and energy balance on Earth's surface. Thermal infrared (TIR) remote sensing can only obtain valid observations under clear-sky conditions, which results in the discontinuities of the LST time series. In contrast, passive microwave (PMW) remote sensing can help estimate the LST under cloudy conditions and the LST generated by PMW observations is an important input parameter for generating medium-resolution (e.g., 1km) all-weather LST. Neural networks, especially the latest deep learning, have exhibited good ability in estimating surface parameters from satellite remote sensing. However, thorough examinations of neural networks in the estimation of LST from satellite PMW observations are still lacking. In this study, we examined the performances of the traditional neural network (NN), deep belief network (DBN), and convolutional neural network (CNN) in estimating LST from the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) and Advanced Microwave Scanning Radiometer 2 (AMSR2) data over the Chinese landmass. The examination results show that CNN is better than NN and DBN by 0.1–0.4 K. Different combinations of input parameters were examined to get the best combinations for the daytime and nighttime conditions. The best combinations are the brightness temperatures (BTs), NDVI, air temperature, and day of the year (DOY) for the daytime and BTs and air temperature for the nighttime. Compared with the MODIS LST, the CNN LST estimates yielded root-mean-square differences (RMSDs) of 2.19–3.58 K for the daytime and 1.43–2.14 K for the nighttime for diverse land cover types for AMSR-E. Validation based on the in-situ LST demonstrates that the CNN LST yielded root-mean-square errors of 2.10–5.34 K and the error analysis confirms that the main reason for the errors is the scale mismatching between the ground stations and the MW pixels. This study helps better the understanding of the use of neural networks for estimating LST from satellite MW observations.

How to cite: Wang, S., Zhou, J., Zhang, X., and Jin, Z.: Estimating Land Surface Temperature from AMSR-E and AMSR2 Data with Convolutional Neural Network, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14126, https://doi.org/10.5194/egusphere-egu21-14126, 2021.

11:16–11:18
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EGU21-14373
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ECS
Jin Ma and Ji Zhou

As an important indicator of land-atmosphere energy interaction, land surface temperature (LST) plays an important role in the research of climate change, hydrology, and various land surface processes. Compared with traditional ground-based observation, satellite remote sensing provides the possibility to retrieve LST more efficiently over a global scale. Since the lack of global LST before, Ma et al., (2020) released a global 0.05 ×0.05  long-term (1981-2000) LST based on NOAA-7/9/11/14 AVHRR. The dataset includes three layers: (1) instantaneous LST, a product generated based on an ensemble of several split-window algorithms with a random forest (RF-SWA); (2) orbital-drift-corrected (ODC) LST, a drift-corrected version of RF-SWA LST at 14:30 solar time; and (3) monthly averages of ODC LST. To meet the requirement of the long-term application, e.g. climate change, the period of the LST is extended from 1981-2000 to 1981-2020 in this study. The LST from 2001 to 2020 are retrieved from NOAA-16/18/19 AVHRR with the same algorithm for NOAA-7/8/11/14 AVHRR. The train and test results based on the simulation data from SeeBor and TIGR atmospheric profiles show that the accuracy of the RF-SWA method for the three sensors is consistent with the previous four sensors, i.e. the mean bias error and standard deviation less than 0.10 K and 1.10 K, respectively, under the assumption that the maximum emissivity and water vapor content uncertainties are 0.04 and 1.0 g/cm2, respectively. The preliminary validation against in-situ LST also shows a similar accuracy, indicating that the accuracy of LST from 1981 to 2020 are consistent with each other. In the generation code, the new LST has been improved in terms of land surface emissivity estimation, identification of cloud pixel, and the ODC method in order to generate a more reliable LST dataset. Up to now, the new version LST product (1981-2020) is under generating and will be released soon in support of the scientific research community.

How to cite: Ma, J. and Zhou, J.: Global long-term land surface temperature for NOAA AVHRR: extension from 1981-2000 to 1981-2020, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14373, https://doi.org/10.5194/egusphere-egu21-14373, 2021.

11:18–11:20
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EGU21-4510
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ECS
Shuang Sun, Donghai Zheng, Shaomin Liu, Ziwei Xu, Tongren Xu, Hui Zheng, and Xiaofan Yang

The Tibetan grasslands has very strong land-air interactions and plays an important role in the regional climate system of the Tibetan Plateau and understanding of land-air interactions in the Tibetan grasslands is significantly important for the sustainable development of it under the climate change. In this paper, we assessed the Noah-MP by conducting ensemble experiments for analyzing the sensitive physical processes, and selected the optimal combinations of parameterization options at four alpine meadow sites in the Tibetan grassland ecosystems. Measurements collected from four study sites over the Tibetan grassland ecosystems in the Heihe Watershed Allied Telemetry Experimental Research (HiWATER) are used. The results showed that the dynamic vegetation (Dveg), the canopy stomatal resistance (Crs), the runoff and the groundwater (Run) and the surface exchange coefficient (Sfc) physical processes are the most sensitive control physical processes for energy and water fluxes in the Tibetan grassland ecosystems. Importantly, the optimal combination of parameterization options in Noah-MP overestimates the sensible heat flux (H) and underestimates soil moisture (θ) obviously. After finding the problems in the simulations outputed by the optimal combination of parameterization options, two groups of improved experiments were conducted to find out the reason. We found that the improved calculation of the surface exchange coefficient can alleviate the overestimation H, and the improved method of soil parameters considering the soil organic carbon (SOC) and an exponential form of root vertical distribution for each soil layers can effectively solve the underestimation of θ at all four sites.

How to cite: Sun, S., Zheng, D., Liu, S., Xu, Z., Xu, T., Zheng, H., and Yang, X.: Assessment and Improvement of Noah-MP over the Tibetan grasslands in growing season, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4510, https://doi.org/10.5194/egusphere-egu21-4510, 2021.

11:20–11:22
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EGU21-7848
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ECS
Ebony Lee and Seon Ki Park

The Noah Land Surface Model (Noah LSM) estimates snow depth using snow water equivalent and snow density. The snow density is determined by snow compaction, snowmelt water storing, and density of fresh snowfall. The Noah LSM usually underestimates snow depth compared to the ground observations in Korea, which occurs from the beginning of snowfall. We performed an optimal estimation of parameters related to the density of fresh snowfall, using micro-genetic algorithm (μ-GA) that uses the evolution process concept through natural selection and mutation mechanism. Ground observations from 36 sites of the Korea Meteorological Administration, for the recent 10 years (May 2009 – April 2019), are used for offline forcing of the Noah LSM and evaluating the fitness function in μ-GA. Optimized parameters reduced the density of fresh snowfall, and improved the simulated snow depth. The root-mean-square error of snow depth decreased from 8.1 cm to 7.1 cm.

How to cite: Lee, E. and Park, S. K.: Optimization of snow density parameter of Noah Land Surface Model using micro-genetic algorithm for estimating snow depth, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7848, https://doi.org/10.5194/egusphere-egu21-7848, 2021.

11:22–11:24
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EGU21-14192
Seung Yeon Lee, Sujung Lim, Ebony Lee, and Seon Ki Park

To improve the predictability of weather/climate models, a prediction system capable of simulating the land surface-atmosphere interaction is essential. In the land surface model (LSM), the parameter values are applied differently depending on the land cover type. Previous studies reported that the Noah LSM underestimated the snow-related variables such as snow albedo, snow depth, and snow cover, compared to actual observations. In this study, among various processes in Noah LSM, we optimize several parameters related to snow albedo, using the genetic algorithm (GA) and satellite (MODIS) data: the parameters to be optimized include 1) the threshold value of the amount of snow with full coverage, , 2) the distribution shape coefficient related to the maximum albedo of new snowfall, and 3) the maximum albedo coefficient. We propose the MODIS data processing method to extract representative snow albedo values, rather than the point (pixel) values, for different land cover types in a 10 km by 10 km area around a model gridpoint ⸺ the representative values are used to calculate the fitness function in the GA optimization. The snow albedo simulation by Noah LSM has alleviated the underestimation problem with the optimized parameter values: it showed better results with the parameter values optimized using the representative values than those optimized using the point values. We expect to see further improvement in the weather/climate simluations using the coupled land surface-atmosphere model (e.g., WRF-Noah LSM) by implementing the optimized parameter values related to snow albedo.

How to cite: Lee, S. Y., Lim, S., Lee, E., and Park, S. K.: Satellite data processing for optimization of snow albedo parameterization in Noah LSM, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14192, https://doi.org/10.5194/egusphere-egu21-14192, 2021.

11:24–11:45