AS2.5

We present the first detailed analysis of multi-seasonal near-surface turbulence observations for an urban area in highly complex terrain. Using four years of eddy covariance data collected over the Alpine city of Innsbruck, Austria, we assess the impact of the urban surface, orographic setting and mountain weather on the exchange of energy, momentum and mass. In terms of urban surface controls, findings indicate several similarities with previous studies at city-centre sites (in much flatter terrain). The available energy is used mainly for the net storage heat flux and sensible heat flux, while the lack of vegetation in the source area means latent heat fluxes are small. Observed carbon dioxide fluxes are dominated by anthropogenic emissions from building heating in winter and traffic in summer. The measured annual total carbon dioxide flux corresponds well to both modelled emissions and observations from other sites with a similar proportion of vegetation, but interpretation of seasonal and diurnal patterns is complicated by spatial heterogeneity in the source area combined with distinct temporal trends in flow conditions.

Innsbruck’s mountainous setting impacts atmospheric conditions and surface-atmosphere exchange in multiple ways. Steep valley sides block solar radiation at low sun angles, resulting in a shift in the times of local sunrise and sunset compared to over flat terrain. In the absence of strong synoptic forcing, a thermally driven valley-wind circulation develops with characteristic daily and seasonal flow patterns. Moderate up-valley winds are observed during the afternoon (these are strongest during summer), while weak down-valley winds prevail overnight, in the early morning and during winter. During spring and autumn, downslope windstorms (foehn) can lead to marked increases in temperature, wind speed and turbulence. Sensible heat fluxes in the city are almost always positive (even at night and during winter), however the presence of warm air above cooler surfaces can result in negative sensible heat fluxes during foehn. Furthermore, very low carbon dioxide mixing ratios observed during foehn events illustrate how the intense mixing helps to ventilate the city and reduce pollutant concentrations.

For the first time, the combined influences of the urban environment, complex orography and atmospheric conditions on surface-atmosphere exchange are analysed in order to begin to understand interactions between urban and topographic processes. These results are thus relevant not only for other urbanised Alpine valleys, but for the numerous cities across the globe which are located in some kind of topographic complexity, such as in river valleys or basins, on hilltops or plateaus or along coastlines.

How to cite: Ward, H. C., Rotach, M. W., Gohm, A., Graus, M., Karl, T., Haid, M., Umek, L., and Muschinski, T.: Surface-atmosphere interactions at an urban site in highly complex terrain, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6065, https://doi.org/10.5194/egusphere-egu22-6065, 2022.

To calculate turbulent fluxes from eddy-covariance measurements, an appropriate filter time needs to be selected to remove non-turbulent larger-scale motions from the raw time series, while retaining all of the turbulent contributions. Common choices include 30 min for convective conditions and 1-5 min for stable conditions. Eddy-covariance data from five i-Box stations in the Austrian Inn Valley are analyzed to determine the appropriate filter time scale under stable conditions using spectral analysis. The i-Box (Innsbruck Box) is a long-term measurement platform, which was designed to study boundary-layer processes in highly complex terrain and has been operational since 2012. The five stations are located in an approximately 6.5-km long section of the 2-3-km wide valley, with one station at the almost flat valley floor, two stations on relatively low-angle slopes of the south-facing sidewall, and two stations on steep slopes of the north-facing sidewall. Different methods, including Fourier analysis and multi-resolution flux decomposition, are tested to determine the filter time scale. As submeso motions affect temperature and the horizontal and vertical wind components differently, not all variances and covariances are equally well suited to identify the time scale. Using the correlation between the identified filter time and the mean near-surface wind speed and stability, the impact of different filter times, including a flexible, time-varying filter time, on near-surface turbulent fluxes is further discussed.

How to cite: Lehner, M. and Rotach, M. W.: Analysis of the filter time scale under stable conditions in mountainous terrain, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2687, https://doi.org/10.5194/egusphere-egu22-2687, 2022.

During the spring of 2020, many countries around the world imposed lockdown measures involving economic activity and movement restrictions to contain the outbreak of the novel coronavirus disease (COVID-19), thereby leading to changes in air pollutant concentrations (Venter et al., 2020). The unprecedented reductions in primary pollutant emissions created a unique opportunity to assess the response of photosynthetic activity of terrestrial ecosystems to atmospheric changes in air quality. Our hypothesis was that a concentration decrease in particulate matter (PM) and the resulting change in light scattering may have affected photosynthesis via changes in direct and diffuse radiation, while a reduction of ozone precursor emissions may have negatively impacted the formation of ozone and reduced its phytotoxic effects. Thus, we analysed turbulent fluxes from eddy covariance measurements and meteorological data collected at the Integrated Carbon Observation System (ICOS) ecosystem stations, and also air pollution data from a continental-scale chemistry transport model (LOTOS-EUROS). Using observations from 44 sites in Europe spanning eleven countries and nine vegetation types, we calculated a 4-month (March-April-May-June, hereafter ‘spring’) anomaly of gross primary productivity (GPP) as the cumulative difference of GPP between 2020 and the reference period from 2015 to 2019. For 34 out of 44 sites, we found that the means between 2020 and the reference GPP were different at the 5% significance level. We further classify these sites into four groups according to modelling and simulation analyses and related data.

• Group 1 included 16 sites where the GPP anomaly was predominantly driven by changes in meteorology. A 7-31% GPP reduction of eight sites in this group was attributed to several different factors such as reduced incoming shortwave radiation (SW_IN), increased vapour pressure deficit (VPD), late growing season and legacy effects. The remaining eight sites experienced an increase in GPP (5-20%) which coincided with increased SW_IN and reduced diffuse fraction (K_d).
• Group 2 consisted of five sites where the GPP anomaly was primarily linked to drought-related effects as indicated by an exceptional increase in the Bowen ratio (δß > 29%), declines in soil water content (SWC) and precipitation.
• Group 3 was represented by five sites where the GPP anomaly was presumably affected by both meteorology and pollutants. All sites in this group experienced an increase in GPP of 14-47% that coincided with enhanced SW_IN (2-13%), reduced atmospheric concentrations of NO₂ (28-47%), NO (33-57%), O₃ (2-3%), SO₂ (5-7%), PM10 (4-14%), PM2.5 (9-17%) and increased NH₃ (1-5%).
• There were eight grassland and savannah sites in Group 4 where the ecosystem management interacted with meteorology to mainly increase GPP by 10-41%.

We first conclude that meteorology and pollutant concentrations during the spring were different between 2020 and 2015-2019 period. Second, our analyses showed that the GPP anomaly in the spring of 2020 was explained by the balance between positive and negative impacts of biophysical drivers. GPP increased when the combined effects of enhanced SW_IN, increased air temperature and reduced pollutant concentrations overtook the negative impact of changes in VPD, SWC and K_d.

Acknowledgements. We would like to thank ICOS site investigators for sharing eddy covariance data.

How to cite: Tang, A. C. I., Flechard, C., Simioni, G., Stoy, P. C., Fares, S., Cuntz, M., Šigut, L., Peichl, M., Mammarella, I., Buchmann, N., Berveiller, D., Douros, J., Timmermans, R., Rebmann, C., Knohl, A., Arriga, N., Taborski, T., Fu, Z., Nilsson, M., and Loustau, D. and the co-authors: Ecosystem gross primary productivity during the COVID-19 lockdown, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8155, https://doi.org/10.5194/egusphere-egu22-8155, 2022.

Urban areas, being a considerate source of CO₂, at the same time are one of the most complicated ecosystems, with some uncertain components still present in the local carbon cycle. Complications with CO₂ dynamics monitoring arise from high heterogeneity of the area and the presence of various sources, but also from a not entirely explored impact of urbanization on the local biosphere. There is a growing need for experimental data to verify existing CO₂ emission inventories and to serve as a reliable input to climate models.

In February 2021, an eddy covariance site was established in Krakow, southern Poland, to investigate CO₂ exchange in its urban ecosystem. The neighborhood of the site is highly heterogeneous, including various anthropogenic sources such as traffic, household heating, and humans themselves; however, a considerable part of the source area is covered with green, including home gardens, a soccer stadium, and a municipal park.

We present a first sight of the CO₂ eddy covariance flux results that were obtained since the site was established. The city is undoubtedly a net CO₂ source. A significant diurnal variation in the CO₂ flux amplitude was observed in the warm season as compared to winter, with the highest positive values during the night and negative values during the day, indicating effective CO₂ photosynthetic uptake. Morning and afternoon traffic peaks were not clearly pronounced: the area is highly heterogeneous and includes other sources as well that may have their own diurnal variability overlapping the traffic signal.

This project has been partially supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 958927, and the subsidy of the Ministry of Education and Science.

How to cite: Jasek-Kaminska, A., Zimnoch, M., Chmura, L., and Bartyzel, J.: CO2 ecosystem-atmosphere exchange in Krakow, Poland – preliminary results from a new European Fluxes Database Cluster EC urban station, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11716, https://doi.org/10.5194/egusphere-egu22-11716, 2022.

This work is based on the energy flux measurements in almond orchards conducted in the framework of a research project focused on the water status monitoring of this crop in semi-arid environments. An eddy-covariance system was installed in a central location of a 11 ha young almond orchard in 2017 and data of the components of the energy balance equation were collected for 3 years. In 2020 the tower was moved to a nearby plot, to monitor a 10 ha mature almond orchard in this case. Both sites are located in Albacete (southeast Spain), and datasets are available through the European Fluxes Database Cluster.

The complex structure of the trees and the small size of the fields are a challenge for the characterization of the surface energy balance in almond orchards. This work analyzes the footprint area contributing to the turbulent flux measurements, as well as the energy balance closure as a function of the canopy height and the instruments deployment. Also, registered CO₂ flux data allows a discussion on the behavior of the almond trees as carbon sinks in these environments.

Flux databases in woody crops are quite scarce in global networks. The measurement site introduced in this work will contribute with valuable flux data to the study of these expanding crops in semi-arid areas.

How to cite: Sánchez, J. M., Simón, L., Rodríguez, A., López-Urrea, R., González, J., Doña, C., Galve, J. M., and Calera, A.: Eddy-covariance measurements and surface energy balance in almond orchards. Results and challenges., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12886, https://doi.org/10.5194/egusphere-egu22-12886, 2022.

Wind machines have been increasingly used for fruit frost mitigation in the agricultural community. The basic idea of using wind machines is to bring the warm air from above to the surface and create mixing. However, the efficiency and physical mechanism of air mixing by wind machines are not fully understood from previous studies. The conclusions from previous studies are usually based on a few point measurements only and therefore limited as to abstract general guidelines. Here, a unique field experiment is presented, with high-resolution (0.25m) temperature probing at the scale of a full orchard. In combination with high-resolution numerical simulation, this allows to better understand the effects of turbulent mixing and to quantify wind machine efficiency.

In the field we employed a 9km optical fiber in two horizontal planes at heights of 1 and 2m above the surface. Through this Distributed Temperature Sensing a meshed grid with resolution of ~0.25m over ~ 6 ha is obtained. This allows to quantify the spatial and temporal variation of temperature dynamics at orchard scale. Some findings can be drawn from experimental observations. Wind machines are proved to be an effective method for frost mitigation. In our experiment, the wind machine reduced 50% and 70% of the inversion strength (7K) in an area of 3.39ha and 0.61ha respectively. The warming area strongly depended on the radial distance to the wind machine, inversion strength and advection intensity. In general, the closer distance to the wind machine, the warmer the air is. However, advection plays an important role in the shape and direction of the warming plume. With only 0.2-0.3m/s weak wind at 3-meter height, the center of the warming plume at 1m height drifted 50m in the downwind direction: The background wind in combination with the wind machine changed the warming plume to an asymmetrical ‘pear shape’.

Numerical simulations were used to investigate the sensitivity of the various settings of the wind machine. Operation modes include full 360 degrees rotation (FR), upwind (UHR) and downwind (DHR) rotation (both 180 degrees). The analysis shows that typically the upwind mode results in better mixing efficiencies than the FR and DHR cases. This may be attributed to the enhanced turbulence that is caused by the shear interaction between the machine jet and the upward wind. The evaluation of different settings of the wind machine showed that all levels of warming are generally insensitive to the rotation period (1.6 to 10min). The setting of tilting angle (9°± 3°) gives optimal warming efficiency for all operation modes. With the finding of the current study, we recommend that farmers and the agricultural community test the effectiveness of the upwind operation.

How to cite: Dai, Y., Boekee, J., van Hooft, A., Schilperoort, B., ten Veldhuis, M.-C., and van de Wiel, B.: Wind machines for fruit frost mitigation: a quantitative 3D investigation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11630, https://doi.org/10.5194/egusphere-egu22-11630, 2022.

Floodplain forests play an important role in strong, mutual and continuous interaction between climate and the ecosystems, despite a relatively small total area of coverage in Europe. They are characterized by a high production level and biodiversity.

In this study we focus on the quantification of CO₂ exchange attributable to the floodplain forest in Lanzhot, Czech Republic. This quantification is a critical requirement in order to estimate the CO₂ balance on a local and regional scale. Lanzhot is a floodplain forest located in South Moravian Region of Czech Republic (48.6815483 N, 16.9463317 E). It’s a 122 years old, mixed deciduous-broadleaf forest. Main species are english oak, narrow-leaved ash and hornbeam. Mean ground water level reaches depth of 2.7 m.

To evaluate the ecosystem-atmosphere CO₂ exchange we apply the eddy covariance (EC) method, which became a key method for measurements of energy and greenhouse gas exchange between ecosystems and the atmosphere. In recent years, case studies focused on testing and validating the applicability of the EC technique above forest ecosystems. The majority of these studies led to the conclusion that above forest canopy derived CO₂ fluxes might be biased due to missing below canopy respiration components in the above canopy signal during periods of insufficient mixing (decoupling) across the canopy. As standard flux filtering methods like the u_* filtering may not account for decoupling sufficiently, additional below canopy EC measurements were suggested to tackle this problem. The key assumption behind such two-level measurements is, that quantities like u_* or the standard deviation of vertical wind velocity exhibit a linear relation during periods of full coupling between below and above canopy air masses.

In this study, we assess different single- and two-level flux filtering strategies with regards to decoupling and its impact on the above canopy derived CO₂ fluxes. The analysis is focused on one year of concurrent below and above canopy EC measurements. Our starting hypothesis was that conventional single-level EC flux filtering strategies like the u_* filtering might not be sufficient to fully capture the forest CO₂ exchange at the studied ecosystem. Initial results suggest that decoupling occurs regularly at the studied floodplain forest. The implication on the above canopy derived EC CO₂ fluxes, however, appears to be negligible. We attribute this to the open canopy and flat EC tower surrounding terrain which inhibits horizontal removal of below-canopy respired CO₂. Overall, our study underlines the need of explicit decoupling investigations at each forest ecosystem, as decoupling is strongly site specific, depending on canopy properties, site meteorology and tower surrounding topography.

How to cite: Kowalska, N. and Jocher, G.: Floodplain forest CO2 exchange – a micrometeorological point of view, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11112, https://doi.org/10.5194/egusphere-egu22-11112, 2022.

The exchange of energy, moisture and momentum between the atmosphere and the land-surface as well as the associated feedback processes are decisive for the development of the planetary boundary layer. Inaccurate representation and parameterization of these processes are a weakness of current weather and climate models. Improvements in these areas will contribute significantly to better simulations of cloud formation on all temporal and spatial scales. This requires simultaneous measurements of the land-atmosphere system in all compartments. Both the LAFE and the new LAFO design with their instrument synergies have already made important contributions to this. With comparisons between model parameterizations and observations, e.g. the applicability of the Monin-Obukhov similarity theory (MOST) in the case of natural heterogeneous land surface can be investigated or new parameterizations can be developed.

The Land-Atmosphere Feedback Experiment (LAFE, Wulfmeyer et al., 2018) was performed in August 2017 as a measurement campaign at the Atmospheric Radiation Measurements (ARM) Program Southern Great Plains site in Oklahoma, USA. For boundary layer observations, scanning Doppler lidar systems for wind measurements, rotational Raman lidar for temperature and humidity measurements, and differential absorption lidar for water vapor measurements were setup. At the land-surface, meteorological and plant dynamics variables, energy balance, and soil moisture and temperature were recorded at eddy covariance stations. These measurements are also executed at the Land-Atmosphere Feedback Observatory (LAFO, lafo.uni-hohenheim.de) at the University of Hohenheim in Stuttgart (Germany) to collect long-term time series in addition to field experiments. Here, lidar measurements are operationally operated and complemented by measurements from a Doppler cloud radar. At the land surface we measure with eddy covariance stations and a network of soil moisture and temperature sensors and the vegetation status is recorded in the study area. This sensor synergy in LAFO is prototype for GLAFOs (Gewex LAFOs, Wulfmeyer et al. 2020) to establish these measurements in different climate regions in the world.

In this contribution, we present the measurement concept and how observations can be used to study and improve boundary layer and turbulence parameterizations. We demonstrate this with measurement results from LAFE and LAFO with estimates of fluxes determined by combining the moisture, temperature, and wind profiles near the ground, allowing the derivation of appropriate similarity relationships for both entrainment fluxes and MOST.

Wulfmeyer et al., 2018, doi: 10.1175/BAMS-D-17-0009.1

Wulfmeyer et al. 2020, GEWEX Quarterly Vol. 30, No. 1.

How to cite: Späth, F., Lange, D., Behrendt, A., Abbas, S. S., Brewer, A., Senff, C., Weber, T., Streck, T., and Wulfmeyer, V.: LAFE and LAFO: New experimental and observational investigations of land-atmosphere feedback processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7498, https://doi.org/10.5194/egusphere-egu22-7498, 2022.

Technology has reached a point where ground-based remote sensing instruments have the ability to greatly increase the spatial and temporal data density compared to conventional instruments. This offers the great opportunity to improve the understanding of individual processes and to increase the predictive capabilities of numerical weather models and reduce their inaccuracies. The goal of this study is to assess these measurement inaccuracies and the usefulness of Doppler lidar systems for these purposes. The data were collected during the FESST@MOL 2020 measurement campaign, organised by the German Weather Service (DWD) and initiated by the Hans-Ertel-Center for Weather Research (HErZ), at the boundary layer field site (GM) of the DWD in Falkenberg (Tauche), Germany. During the measurement campaign, a total of eight Doppler lidars of the brands Halo Photonics and Leosphere were active in different operating modes. We compare the results of triple and single Halo Photonics lidar setups and triple Leosphere lidar setups with the measurements of an ultrasonic anemometer mounted at a height of 90 m at the 99 m high instrumented tower in Falkenberg. The focus of the operating modes was on various virtual tower (VT) measurements and velocity azimuth display (VAD) measurements with the different averaging times of ten and thirty minutes for the mean horizontal wind. The discrepancy in readings between VT and VAD measurements increases with increasing height above the ground while the Halo Photonic lidars performed better in the comparison with the sonic anemometer.

How to cite: Wolz, K., Wildmann, N., Beyrich, F., Päschke, E., Detring, C., and Mauder, M.: Comparison of wind measurements from different Doppler lidar scan strategies and two lidar brands with an ultrasonic anemometer, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5441, https://doi.org/10.5194/egusphere-egu22-5441, 2022.

Ammonia (NH₃) plays an important role in atmospheric and environmental chemistry, from the formation of inorganic and organic aerosol, to soil acidification and nutrient cycles. Its dominant source are anthropogenic emissions, primarily from agricultural activities, and it thereby contributes substantially to fine-particle pollution in many regions. However, there are high uncertainties in attributing atmospheric NH₃ to specific sources, and current emission inventories substantially underestimate many major point sources. The quantification of NH₃ is challenging, due to the wide range of ambient mixing ratios and its infamous propensity to interact with surfaces, causing losses and slow response times.

In this study, we present a new technique for detecting NH₃ using a chemical ionization mass spectrometer (CIMS). The CIMS was deployed on a G-1 aircraft during the Holistic Interactions of Shallow Clouds, Aerosols, and Land Ecosystems (HI-SCALE) campaign over Oklahoma, specifically around the ARM Southern Great Plains field site, in 2016. The instrument was modified to enable quantifiable airborne measurements throughout tropospheric pressures, and to alternatingly use iodide anion and deuterated benzene cation ionization. In this mode, and aided by a high-flow core-sampling setup, we obtained a formidable device for measuring in-situ mixing ratios of NH₃. Measured NH₃ mixing ratios spanned from <10 to 100s of parts per trillion in the free troposphere, to sharp plumes of highly elevated mixing ratios (10’s of parts per billion) downwind from a fertilizer plant. These plumes are of the order expected based on the U.S. Environmental Protection Agency’s National Emissions Inventory (NEI). The high sensitivity and response time of ~1 s allowed us to also calculate vertical NH₃ fluxes via eddy covariance. We used the continuous wavelet transform method to maximize the spatial resolution of the derived fluxes, remaining limited to ~1-2 km by the flight altitudes and related turbulence scales. Together with flux footprint considerations, the measurements let us constrain the NH₃ emission rates for ubiquitous agricultural area sources in rural Oklahoma. Typically, the derived area emission rates clearly exceeded the values provided by the NEI. In addition, our measurements captured large point sources that appeared to be missing in the NEI, at least one identified as a large cattle farm.

How to cite: Schobesberger, S., D'Ambro, E. L., Lee, B. H., Peng, Q., Pekour, M. S., Fast, J. D., and Thornton, J. A.: Airborne flux measurements of ammonia over the Southern Great Plains using chemical ionization mass spectrometry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7295, https://doi.org/10.5194/egusphere-egu22-7295, 2022.

The present paper explores the role that nocturnal low-level jets exert on the lower nocturnal boundary layer. In particular, this paper investigates their role in the modulation of surface turbulence near the surface. This presentation also discusses the controversy regarding the existence of atmospheric shear sheltering over contrasting surfaces. In a seminal experiment aimed at validating the Hunt and Durbin (1999) theory, Smedman (2004) reported the existence of shear sheltering in real atmospheric conditions. However, other existing studies did not find any evidence of eddy blocking in the presence of a low-level jet near the ground despite the use of large datasets and contrasting environmental conditions. In this present presentation, an explanation is offered in the present study which reconciles all three experimental studies, thus elucidating the apparent contradiction. Furthermore, this paper conclusively supporting the presence of shear-sheltering in the presence of low-level jet. Implications for surface-atmosphere exchange in contrasting surfaces and atmospheric stabilities are discussed.

How to cite: Leclerc, M. Y. and Zhang, G.: Shear-Sheltering and Its Impact on Atmospheric Turbulence, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13266, https://doi.org/10.5194/egusphere-egu22-13266, 2022.

Atmospheric water, or non-rainfall water inputs (NRWIs) are an important source of water in arid areas. Considering the large surface area of arid and extremely arid regions, NRWIs are a critical, albeit largely overlooked, component of the global hydrological cycle.  Water vapor adsorption is not only the least studied form of NRWI but likely the most common one in arid areas. The amount of water vapor adsorption mainly depends on the gradient between water vapor pressure between the air (e_a) and the soil (e_s).  Sea breeze, which carries moist air from the sea landward, can result in a significant daily increase in e_a in desert areas. 

We have examined the diurnal cycle of soil water content derived by water vapor adsorption and evaporation in two very different deserts: the Negev (loess soil, ~100 mm y^-1) and the Namib (sand dunes, ~20 mm y^-1).  Water vapor adsorption into the Negev’s loess soil has been established as the dominant NRWI (with 0.3-0.5 mm night^-1). Even in the Namib, which is known as a fog desert, even on nights with fog, at least half of the water accumulation occurred via water vapor adsorption, before the onset of fog (0.1-0.2 mm night^‑1).  

How to cite: Agam, N. and Kool, D.: Water where there is no water – Atmospheric water captured by world deserts, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12343, https://doi.org/10.5194/egusphere-egu22-12343, 2022.

In arid and semiarid environments non-rainfall water inputs (NRWI) are an important source of water. In Israel's Negev desert direct absorption of atmospheric water vapor is the dominant NRWI and is strongly affected by soil properties, in particular clay content. The presence of a surface crust layer, whose physical and physico-chemical properties are substantially different from those of the underlying undisturbed substrate will likely affect the absorption patterns.  The objective of our study was to quantify the effect of soil type (loess vs. sand) and crust cover (crust vs. crust removed) on direct atmospheric water absorption.

The loess soil samples were obtained in an open field adjacent to the Jacob Bluestein Institutes for Desert Research (BIDR), Ben-Gurion University of the Negev (30˚51’ N, 034˚46’ E, 470 m a.s.l); and the sand samples from the Nizzana Sand Dune area (30˚58’N, 034˚24’E, 226 m a.s.l.).  The loess crusts were physically induced while those present on the sand samples were of biological origin.

A field experiment was carried out in the open field adjacent to the BIDR.  Four undisturbed 0.5 m depth soil samples (sand and loess with crust and with crust removed) were placed in micro-lysimeters and automatically weighed at 30 min. intervals.  This field experiment was carried during the dry season of May to October 2016.

The field study was supplemented with a laboratory experiment in which undisturbed samples (1,3, 7 and 10 cm) obtained from the above mentioned sites were used. Oven-dry samples were exposed during 6 days to constant temperature and relative humidity conditions (25±1 ^oC and  85±5 %, respectively)  in sealed chambers.  Mass changes were recorded at varying time intervals.   

The adsorption process in the field started in the late afternoon with the arrival of the sea breeze and ended with sun rise. On a daily basis the crusted loess sample adsorbed more water than the crusted sand sample, and the crust removed loess soil absorbed more water than the crust removed sand.  The crusted samples generally absorbed less water than the corresponding non-crusted ones.

The results of the laboratory tests showed that loess samples with crust and with crust removed absorbed similar water amounts for all sample depths throughout the study period. The crusted sand samples however absorbed systematically more water than the crust removed samples for all sample depths.

We conclude that the higher resistance of crusts to gaseous flux, a result of their higher bulk density and smaller pores, does not limit water vapor flux into the deeper soil layers and does not explain the field results.  

How to cite: Berliner, P., Neuberger, C., Anxia, Y., and Nurit, A.: The effect of soil type and crust cover on the absorption of atmospheric water vapor – laboratory and field trials., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11198, https://doi.org/10.5194/egusphere-egu22-11198, 2022.

Globally, ecosystems are water-limited on about one-third of the land area. In these ecosystems, it has been shown that even small water inputs often play a relevant role for a large number of species ensuring their survival. However, to date, such inputs from fog, dew, and adsorption of atmospheric water vapor, which are summarized as non-rainfall water input (NRWI), can rarely be studied because the necessary measurement infrastructure is scarce. Long-term measurements covering multiple seasons and years are especially rare. This limits our understanding of the role of NRWI in the surface water, energy, and carbon balance in ecosystems. 

In this contribution, we investigate surface water exchange processes in a semi-arid Savannah ecosystem over a period of a year. Five large high precision weighing lysimeters enable us to analyze water phase changes with a temporal resolution of five minutes. 

Our main finding is that across (almost) all seasons diel dynamics were characterized by evaporation at daytime and condensation at nighttime. Condensation processes varied between seasons. In winter, dew and fog regularly formed at night when soil moisture and atmospheric humidity were close to saturation. In summer, despite high mean night conditions of atmospheric vapor saturation deficit (15 hPa), water input via adsorption of atmospheric vapor formed due to dry topsoil moisture (< 10 %). In total NRWI occurred for at least 3 hours per day on 297 days (81 % of the year) with a mean duration of 6 hours per day. The relative contribution of NRWI to the total annual water input was 8 %. However, we found a large seasonal variability, with adsorption forming the major water input to the ecosystem during the summer drought period. In the year analyzed, it compensated for 19 % of the evaporation losses. 

Our results suggest a non-negligible contribution of NRWI to the water budget of a semi-arid ecosystem. Consequently, a better representation of the diel dynamics of evaporation and condensation could help us to increase our knowledge of eco-hydrological processes in semi-arid ecosystems. Especially during the dry season, data from daytime and nighttime hours should be taken into account in order not to bias the water balance towards evaporative losses.

How to cite: Paulus, S. J., El-Manday, T. S., Orth, R., Hildebrandt, A., Wutzler, T., Carrara, A., Moreno, G., Perez-Priego, O., Kolle, O., Reichstein, M., and Migliavacca, M.: Frequent water inputs to a semi-arid ecosystem at night - a lysimeter based study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10003, https://doi.org/10.5194/egusphere-egu22-10003, 2022.

Abstract: Large eddy simulations (LES) are performed to better understand the airflow, structure, and mixing processes in the stable boundary layer (SBL) in the bottom of a mid-range mountain valley, Fitchelgebirge, in Southern Germany. The simulated structure and evolution of the SBL over the complex terrain agreed well in comparison with the remote sensing measurements. The simulations were tested using different vertical grid spacings of 10 m, 5 m and 2 m and a stretched version starting at 1 m assuming flat terrain. The topography of the experimental site is complex with mountain ranges of around 700 m on the north and up to 1km on the south. There is a gap on the western side of the site where channel flows are possible. Additional simulations were conducted with topography from a digital elevation model containing elevational differences up to 400 m. Results showed an increased depth of the cold-air pool by up 30 m and lower near-surface temperatures with differences exceeding 5 K in the valley bottom when comparing topography against flat-terrain simulations. The structure of the cold-air drainage followed terrain contours indicating local slope flows being responsible for the enhanced cooling when topography was included, while flat-terrain runs showed no evidence of a coherent cold-air layer. Finer grid resolutions showed much improvement in the resolved cold-pool vertical and horizontal structure. LES output was also compared with in-situ and remote sensing observations in terms of hourly mean profiles of wind speed, direction, and potential temperature, and turbulence kinetic energy. The results highlight the importance of including the topography in SBL modeling for e.g. frost damage forecast, air-pollution studies, fog analyses, and computing greenhouse gas budgets since both the SBL turbulence and time-averaged flow are governed by the thermal structure which is forced by topography even in relatively gentle mountainous terrain in mid-latitude regions.

How to cite: Muppa, S. K., Lapo, K., Sungur, L., Babel, W., and Thomas, C.: Investigating the impact of topography on the stable boundary layer structure over complex terrain using Large eddy simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7620, https://doi.org/10.5194/egusphere-egu22-7620, 2022.

We investigate the diurnal variability in and above the Amazonia rainforest for a representative day during the dry season period. We combine high-resolution large-eddy simulations constrained and evaluated against a comprehensive observations gathered during the field experiment GOAMAZON14.

Our findings quantified the large variability of the photosynthesis drivers in the canopy. This leads to a large scatter on the values of the leaf conductance with minimum and maximum values that vary more than 100% from the average value. The impact of turbulence on the fluxes of heat, moisture and carbon dioxide differs: at the canopy top, we found more strike structures related to wind at the canopy-atmosphere interface whereas at the canopy bottom the structure remind the ones of convective cells. In systematically comparing with the observations, we find that the agreement with observations depend very much on the variable. We find the best spatiotemporal agreement with variables related to wind. The heat distribution and fluxes compare also satisfactorily with the observations. The increasing of complexity on the biophysical processes, related to ecophysiology and soil and the atmospheric control, leads to the largest disagreement between observations and simulation results for evaporation, carbon dioxide plant assimilation and soil efflux. Though the model is able to capture the correct dependences, the magnitude still differ.  We discuss here the need to revise and adjust the leaf and soil models as well as to set a more comprehensive observational strategy to advance our understanding at leaf and canopy levels, and their coupling with the atmosphere.

How to cite: Vila-Guerau de Arellano, J., Pedruzo-Bagazgoitia, X., Moene, A., Ouwersloot, H., Gerken, T., Machado, L., Martin, S., Patton, E., Sorgel, M., Stoy, P., and Yamasoe, M.: Investigating the diurnal radiative, turbulent and biophysical processes in the Amazonian canopy-atmosphere interface by combining LES simulations and observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-835, https://doi.org/10.5194/egusphere-egu22-835, 2022.

Land surface heterogeneity affects the distribution of energy from incoming solar radiation, and in conjunction with ambient winds, influences the convective atmospheric boundary layer development. In this study, experimental large-eddy simulations were carried out applying continuously-distributed soil moisture along a river corridor with idealized initial atmosphere conditions at a spatial scale on the order of kilometers. Simulations were performed with ambient wind ranging from 0 to 16 m/s and for different directions, which are cross-valley and parallel-valley. After decomposing the simulated winds into the ensemble-averaged wind, phase wind, and turbulence, the results show that soil moisture heterogeneity induces a well-organized secondary circulation structure with the horizontal mesoscale phase wind approaching some 2 m/s. The secondary circulation structure persists under the parallel-valley wind conditions independently of the wind speed, but is destroyed when the cross-valley wind is stronger than the horizontal mesoscale phase wind. We explored the relationship between the secondary circulation strength, expressed as the normalized maximum of the vertical phase wind variance, and dimensionless variables such as Bowen ratio and stability parameter (ratio of boundary layer depth and Obukhov length). With the mean of these dimensionless variables, we found a distinct relationship between the strength of the secondary circulations with respect to the ambient wind.

How to cite: Zhang, L., Poll, S., and Kollet, S.: Large-eddy Simulation of Surface Heterogeneity Induced Secondary Circulation with Ambient Winds, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5533, https://doi.org/10.5194/egusphere-egu22-5533, 2022.

Earth System Models (ESMs) traditionally operate at large horizontal resolutions, on the order of 100km, which can obscure the effects of smaller scale heterogeneity. The literature, as well as work in the Coupling of Land and Atmospheric Subgrid Parameterizations (CLASP) project, indicates that surface heterogeneity, particularly in surface fluxes, has important implications for not only surface processes but atmospheric processes as well. Previous work using large-eddy simulation (LES) shows that spatial variability in surface heating can produce significant secondary circulations that are closely related to the type and scale of heterogeneity and are not currently captured by single column sub-grid atmospheric parameterizations used in ESMs.. This presentation aims to address this persistent weakness by using a multi-column approach, where two single column models, one over a high sensible heat flux portion of a climate gridcell domain and another over a low sensible heat flux portion, are coupled through a modeled secondary circulation. 

To accomplish this task, we run the Cloud Layers Unified By Binomials (CLUBB) standalone single column model over a 100 km box centered at the Southern Great Plains site in Oklahoma for a variety of surface and atmospheric conditions both as a single column model, and with two coupled columns. Results are also compared to LESs that use a homogeneous surface flux field and LESs that use realistic, high resolution surface flux fields. Initial results focus on liquid water path (LWP) response to added heterogeneity for 43 day long simulations. We observed qualitatively similar responses in LWP as a result of accounting for heterogeneity induced secondary circulations in both LES and multi-column CLUBB as well as indications of clear trends in response based on the atmospheric conditions. This work indicates that a multi-column setup has significant promise for modeling the impacts of heterogeneity induced secondary circulations for application in ESMs at a fraction of the computational expense of LES. Continuing work expands this analysis to cover a wider variety of surface and atmospheric conditions, determine when multi column CLUBB has significant sensitivities to heterogeneity induced secondary circulations, and explore avenues for further simplification of the model setup.

How to cite: Waterman, T., Bragg, A., Simon, J., and Chaney, N.: Capturing the Effects of Surface Heterogeneity Induced Secondary Circulations on the Lower Sub-grid Atmosphere in Earth System Models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10646, https://doi.org/10.5194/egusphere-egu22-10646, 2022.