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Atmospheric Boundary Layer: From Basic Turbulence Studies to Integrated Applications

Driven by atmospheric turbulence, and integrating surface processes to free atmospheric conditions, the Atmospheric Boundary Layer (ABL) plays a key role not only in weather and climate, but also in air quality and wind/solar energy. It is in this context that this session invites theoretical, numerical and observational studies ranging from fundamental aspects of atmospheric turbulence, to parameterizations of the boundary layer, and to renewable energy or air pollution applications. Below we propose a list of the topics included:

- Observational methods in the Atmospheric Boundary Layer
- Simulation and modelling of ABL: from turbulence to boundary layer schemes
- Stable Boundary Layers, gravity waves and intermittency
- Evening and morning transitions of the ABL
- Convective processes in the ABL
- Boundary Layer Clouds and turbulence-fog interactions
- Micro-Mesoscale interactions
- Micrometeorology in complex terrain
- Agricultural and Forest processes in the ABL
- Diffusion and transport of constituents in the ABL
- Turbulence and Air Quality applications
- Turbulence and Wind Energy applications

Solicited Speakers:

- Dr. Fabienne Lohou, Laboratoire d’Aérologie, Université de Toulouse, CNRS, UPS, France:
" Model and Observation for Surface Atmosphere Interactions (MOSAI) project”.

- Dr. Aaron Boone, CNRM-Université de Toulouse, Météo-France/CNRS, France:
“Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment (LIAISE) Project: Overview of the Field Campaign intense phase”.

- Dr. Alexander Baklanov, World Meteorological Organization (WMO), Science and Innovation, Geneva, Switzerland: “Scientific legacy of Sergej Zilitinkevich for boundary layer research and modelling”.

Convener: Carlos Yagüe | Co-conveners: Maria Antonia Jimenez Cortes, Marc Calaf
| Mon, 23 May, 08:30–11:40 (CEST), 13:20–14:40 (CEST)
Room M2

Mon, 23 May, 08:30–10:00

Chairpersons: Carlos Yagüe, Maria Antonia Jimenez Cortes

Mary Rose Mangan et al.

The LIAISE experiment (Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment) was conducted during the summer of 2021 in the Pla d’Urgell region of the Ebro River Valley in Catalonia, Spain (Boone et al., 2021).  In the LIAISE experimental region, the surface was homogeneous at the field scale (e.g. fields of alfalfa); however, the surface was heterogeneous at the regional scale (~10-100km) because of the spatial distribution of irrigated crops and dry natural vegetation.  During the LIAISE experiment, there were extensive observations of both the surface and the boundary layer in the dry and irrigated landscapes.  The observed boundary layer is formed through a composite of surface fluxes from both the irrigated and rainfed surfaces.  Likewise, the observed surface fluxes of individual fields in both regions are controlled by both the surface properties and the regional boundary layer characteristics. 

In this study, we examine the impact of the boundary layer on surface fluxes at two of the LIAISE sites: one in the irrigated, crop-covered area and one in the dry, naturally-vegetated area.  We use an atmospheric mixed-layer column model (CLASS, Vilà-Guerau de Arellano et al., 2015) that is heavily constrained by the surface and boundary layer observations from the LIAISE experiment.  The modeling approach consists of two steps: first the boundary layer was modeled using a composite surface to mimic the landscape scale processes as a control, then a local perspective was adopted to investigate the drivers of evaporation in both the irrigated and rainfed areas.  At the local scale, we use a parameterized evaporation tendency equation introduced by van Heerwaarden et al., 2010 for both model data and observations.  This equation is used both to evaluate the time tendency of boundary layer feedbacks to evaporation and to diagnose the causes of local evaporation tendency.  This approach allows us to quantify the relative importance of the boundary layer controls on evaporation compared to other controls on evaporation (e.g. radiation and advection) at the field scale.


Boone, A., Bellvert, J., Best, M., Brooke, J., Canut-Rocafort, G., Cuxart, J., Hartogensis, O., Le Moigne, P., Miró, J. R., Polcher, J., Price, J., Quintana Seguí, P., & Wooster, M. (2021, December). Updates on the International Land Surface Interactions with the Atmosphere over the Iberian Semi-Arid Environment (LIAISE) Field Campaign. GEWEX News, 17–21.

van Heerwaarden, C. C., Vilà-Guerau de Arellano, J., Gounou, A., Guichard, F., & Couvreux, F. (2010). Understanding the Daily Cycle of Evapotranspiration: A Method to Quantify the Influence of Forcings and Feedbacks. Journal of Hydrometeorology, 11(6), 1405–1422. https://doi.org/10.1175/2010JHM1272.1

Vilà-Guerau de Arellano, J., van Heerwaarden, C. C., van Stratum, B. J. H., & van den Dries, K. (2015). Atmospheric Boundary Layer: Integrating Chemistry and Land Interactions. Cambridge University Press.

How to cite: Mangan, M. R., Hartogensis, O., and Vilà Guerau de Arellano, J.: Evaporation Controlled by Boundary Layer Feedbacks in an Irrigated Semi-Arid Environment: a LIAISE Modeling and Data Study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12283, https://doi.org/10.5194/egusphere-egu22-12283, 2022.

Maria A. Jimenez et al.

Land surface-atmosphere interactions determine the atmospheric boundary layer (ABL) features, and in the case of semi-arid regions the water availability in the upper ground strongly conditions the surface energy balance and in general the observed dominant processes. In the Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment project (LIAISE, Boone et al. 2021), an observational campaign took place in the eastern Ebro river sub-basin between spring and fall 2021 to study the land/atmosphere interactions and the effect of the surface heterogeneities on the ABL in a semi-arid environment, enclosing a large irrigated area in summer. The combined analysis of the ground-based observations, ABL atmospheric measurements (including aircraft and remote-sensing data) and modelling is expected to improve the understanding of processes affecting exchange fluxes between the surface and the atmosphere, especially evapotranspiration, and to allow exploring the local and mesoscale circulations induced by the surface heterogeneities.

A first mesoscale modelling inter-comparison for a summer event in the LIAISE area is intended to evaluate the performance of the participating models compared to the observations and explore the differences between them. Participant models are run at their standard configurations to evaluate the representation of the surface features in the numerical models and its impact in the organisation of the flow at lower levels. Besides, some sensitivity tests are made (initial and lateral boundary conditions, resolution or representation of the surface features, among others) to identify the importance of some model parameters in the model results.

Four models participate in the inter-comparison: MesoNH, WRF, UKMO Unified Model and MOLOCH. They are run with similar horizontal (2km x 2km and 400m x 400m for the outer and inner domains) and vertical (2m at lower levels and stretched above) grid meshes. A 48-h integration is made between 16 and 18 July 2016 for a case under a high-pressure system centred over NW France, with well-developed thermally-driven circulations in the Ebro Basin. Sea breezes are found at the coast and seem to reach the basin after surmounting the mountain coastal range.

Model results are validated using data from the surface stations of the Servei Meteorològic de Catalunya network (very dense in the studied region). It is found that each model has a different representation of the surface heterogeneities affecting the grid values of the surface fluxes. Nevertheless, the mesoscale circulations generated by the models are very close being the differences lying mostly at smaller scales, namely the ABL characteristics, the values of the exchange fluxes at the surface or the state of the surface and the soil. The challenge at this point is to relate the model biases to the particularities of the parameterisations and of the physiographic data bases used by each model. This model inter-comparison is expected to point improvements in the definitions of the setup of each model for a later phase, when the model simulations will be validated using observations from the recent LIAISE experimental field campaign.

How to cite: Jimenez, M. A., Cuxart, J., Grau, A., Boone, A., Donier, S., Le Moigne, P., Miro, J. R., More, J., Brooke, J., Best, M., Tiesi, A., and Malguzzi, P.: Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment project (LIAISE): results for the 1st modelling inter-comparison , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11031, https://doi.org/10.5194/egusphere-egu22-11031, 2022.

Mathilde Jomé et al.

The earth’s surface and its properties impact, on different scales, the atmosphere. Thus, understanding the interactions between the surface and the atmosphere is important to establish and control global and regional numerical models. As a matter of fact, in February 2019, the Working Group on Numerical Experimentation (WGNE) reported that the bias observed on surface convective fluxes were the second source of errors in global and regional numerical models.

Reducing these errors by getting a better understanding of the impact of the surface-atmosphere interactions over heterogenous land surface is one of the main objectives of the Models and Observations for Surface-Atmosphere Interactions (MOSAI) project. Because experimental set-up that would help to study the impact of surface heterogeneity on surface convective fluxes is quite expensive, we tested a new method, based on Artificial Neural Networks (ANNs), that be proved efficient, in previous studies, in estimating surface convective fluxes at low cost. Standard low-cost meteorological stations are associated with higher-cost surface Eddy-Covariance flux stations so that station measurements can be paired to train the network on estimating surface fluxes based only on classical meteorological variables. Based on this, one may then estimate fluxes using this method on a set of various vegetation covers at the same time.

The first step is to test ANNs on well-known data. Two different datasets are used. The first one (twelve discontinuous sunny days), is a control dataset and allows to perform three type of tests to improve the estimated fluxes. The first group of tests concerns the influence of the training dataset, the second one concerns the topography of the network, and, the last one focuses on the choice of the input meteorological variables. The second dataset helps to deepen this study. The aim is to run the same tests but with a longer dataset (a dataset spanning over the course of an entire year, allowing for larger weather conditions) to propose some experimental deployment plan of the meteorological stations network and the Eddy-covariance station for the training of these stations, to apply this method to a future campaign. The first results proved for both datasets that estimating surface convective fluxes with ANNs using only a few variables and a simple topography is possible and would allow long-term monitoring of the surface energy fluxes over an heterogeneous surface.

How to cite: Jomé, M., Lohou, F., Lothon, M., Kelley, J., and Pardyjak, E.: Using Artificial Neural Network to estimate surface convective fluxes., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11095, https://doi.org/10.5194/egusphere-egu22-11095, 2022.

Stanisław Król and Szymon Malinowski

Clouds are the source of the biggest uncertainty in weather and climate models. One cannot fully understand clouds without understanding turbulence and microphysical processes in clouds. During EUREC4A experiment in 2020, data from cloud penetrations and ABL was collected using Twin-Otter aircraft. Data gathered using UFT2b thermometer, a device able to measure temperature with centimeter-scale resolution (temporal frequency of 2 kHz, assuming ~60 m/s aircraft speed), contains valuable information about turbulence and cloud dynamics during various cloud penetrations. Using Recurrence Quantification Analysis, a tool used to analise time series in order to study linearity and chaos in the system, we extract information about regimes present in clouds in terms of mixing of cloud air with enviromental air, and possible chaotic or deterministic behavior. The analysis also enables to divide and classify portions of cloud in terms of turbulence. Criteria for cloud division and classification will be discussed, which will be illustrated by selected examples of recurrence plots and characteristic quantities in various regimes.

How to cite: Król, S. and Malinowski, S.: Recurrence Quantification Analysis of temperature time series from marine cumulus clouds during EUREC4A, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4094, https://doi.org/10.5194/egusphere-egu22-4094, 2022.

Robert Grosz et al.

During the EUREC4A campaign high (up to 3 mm) resolution temperature time series have been collected with the UFT-2 (Ultra-Fast-Thermometer) onboard the BAS Twin Otter aircraft in the subtropical low atmosphere in and between trade wind warm cumulus clouds. The measurements covered a wide range of atmospheric conditions, from cloud interiors, through cloud shells, air spaces between the clouds, as well as the atmospheric boundary layer. Data, resolving scales down the dissipation range allow to estimate temperature dissipation rate (TD) directly from the recorded signal. Examples of temperature fluctuations and associate TD records, characteristic to the various atmospheric conditions, will be presented and discussed.

How to cite: Grosz, R., Król, S., Nowak, J., and Malinowski, S.: Temperature dissipation in convective clouds during EUREC4A, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4222, https://doi.org/10.5194/egusphere-egu22-4222, 2022.

Marcel Schröder et al.

The energy dissipation rate is one of the most important characteristics of a turbulent flow across the entire range of scales, and of particle-turbulence interaction. To investigate cloud microphysics and turbulence in clouds and in the atmospheric boundary layer, we infer coarse-grained time series of the energy dissipation rate from one-dimensional wind velocity time records by specially developed airborne platforms, the Max-Planck-CloudKite + (MPCK+) and the mini-Max-Planck-CloudKites (mini-MPCK). During the EUREC4A-ATOMIC field campaign in the Caribbean January - February 2020, both instruments are deployed aboard balloon-kite hybrids launched from RV Maria S. Merian and RV Meteor conducting in situ measurements of the wind velocity and meteorological as well as cloud microphysical properties with high spatial and temporal resolution. We present estimates of the energy dissipation rate from in situ velocity time records by the MPCKs during the EUREC4A-ATOMIC field campaign and preliminary assessment of turbulence features.

How to cite: Schröder, M., Nordsiek, F., Schlenczek, O., Ibañez Landeta, A., Güttler, J., Bodenschatz, E., and Bagheri, G.: Energy Dissipation Rate Estimates from Airborne Atmospheric Measurements with the Max Planck CloudKites, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12458, https://doi.org/10.5194/egusphere-egu22-12458, 2022.

Christoph Thomas et al.

Mid-latitude atmospheric boundary layers (ABL) in complex, mountainous terrain are often complicated because the large-scale radiative and dynamic forcings are modulated by local-scale forcings which may dominate the near-surface transport. The large-scale forcings of interest in our study are geostrophic winds and cloudiness which are known to cause variations in ABL depth and vertical coupling. The local-scale forcings we investigate are the slope, aspect, and land cover of valley shoulders and bottom which can create high-density cold airflows and pools often associated with submeso-scale motions. These topography-related phenomena may lead to vertical decoupling between the surface, the surface layer and the ABL in absence of strong large-scale synoptic forcing. Understanding the mechanisms by which the large-scale synoptic and local-scale topographic forcings interact has remained poorly understood despite many observational and modeling studies, but is crucial to understanding and quantifying mass and heat exchange in locations to weak winds.

We present results from the Large eddy Observation Voitsumra Experiment (LOVE) in summer 2019 conducted in a mid-range mountain valley in the Fichtelgebirge mountains, Germany over a two-month period as part of the ERC DarkMix project. Observations consist of fine to medium-scale (1s to 10 min) measurements from ground-based remote sensing including a ceilometer (150 to 8000 m above ground), wind Lidar (80 to 800 m above ground), and Sodar-Rass (15 to 300 m above ground) in combination with sonic anemometry and fiber-optic distributed temperature and wind sensing. The objective is to identify the mechanisms by which the land surface gets coupled or decoupled from the near-surface air aloft eventually forming the ABL, stable boundary layer, or residual layer. Particular attention is given to the stable weak-wind flow regime often persisting from sunset to sunrise. 

We test the following two hypotheses: (1) The observed meandering of the near-surface nocturnal flow in the lowest tens of meters is the result of three competing flow modes generated by cold-slope flows from a closely co-located valley slope by net-radiative cooling, an along-valley flow supported by a weak synoptic pressure gradient, and a colder-air pool collecting at the valley bottom. Differences in the relative temperature of the three modes cause quasi-oscillatory variations in static stability and thus vertical coupling. (2) Erosion of the near-surface inversion starts well before arrival of the direct shortwave radiation at the valley bottom caused by radiative warming of the surrounding mountain slopes and enhanced mixing from aloft. As a result, coupling the land-surface to the evolving ABL may be achieved earlier than anticipated from the local surface energy balance in the valley bottom.

How to cite: Thomas, C., Freundorfer, A., Lapo, K., Muppa, S., Olesch, J., and Schneider, J.: Observing vertical coupling near the surface in a shallow mid-range mountain valley using a suite of ground-based remote sensing and tower observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4098, https://doi.org/10.5194/egusphere-egu22-4098, 2022.

Carlos Yagüe et al.

The pollutant concentration close to the surface at specific sites of a city depends on multiple factors. However, disentangling the relative importance of them using observational data is not an easy task. To deepen into these relationships, in this study we use intensive and multiple data from several urban field campaigns that were developed in the city of Madrid (Spain) during 2020 and 2021 under the framework of the AIRTEC-CM (*) research project (Urban Air Quality and Climate Change Integral Assessment).
Among the most typical pollutants in cities, the nitrogen dioxide (NO2) is of crucial importance due to its negative impacts on human health. The diurnal cycle of this pollutant is closely related to the anthropogenic emissions in the area and to the local meteorology, as well as to the turbulent transfers in the atmospheric boundary layer. In this work, we analyse the relation between the NOconcentration and different meteorological variables, including some turbulent parameters calculated from sonic anemometers: turbulent kinetic energy (TKE) and friction velocity (U*). In this sense, we have distinguished those situations where the turbulent parameters are more valuable (have better correlation) than the wind speed, which is the meteorological variable typically used to be correlated with the pollutant concentration.
The analysis of the data clearly reveals how the highest NO2 concentrations are associated with fair-weather (stable) synoptic conditions, as it is already known and expected. However, the detailed analysis of the diurnal cycle in these periods also highlights how the stability favours the appearance of mesoscale diurnal winds (mountain breezes) in the city, increasing the turbulence close to the surface and favouring the pollutants dispersion. This is of key importance because in some cases these processes are not correctly simulated by numerical models, which could lead to wrong predictions (overestimation) of the pollutant’s concentrations at specific hours. Specifically, the evening transition and the following hours during stable conditions are the most difficult periods, displaying the highest and quicker variability in NO2 concentration: very high concentration during calm periods in the transition followed by a rapid cleaning of the air a few hours later due to the breeze appearance.


(*) AIRTEC-CM research project (S2018/EMT-4329) is funded by The Regional Government of Madrid (Spain).

How to cite: Yagüe, C., Román-Cascón, C., Ortiz, P., Sastre, M., Maqueda, G., Serrano, E., Artíñano, B., Gómez-Moreno, F. J., Díaz-Ramiro, E., Alonso, E., Fernández, J., Borge, R., Narros, A., Cordero, J. M., García, A. M., and Núñez, A.: How do the local meteorology and turbulence influence the nitrogen dioxide concentration in Madrid?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10292, https://doi.org/10.5194/egusphere-egu22-10292, 2022.

Antoni Grau Ferrer and Maria A. Jiménez

The island of Mallorca (western Mediterranean Sea) is taken in this work to statistically characterize some of the physical mechanisms involved during Sea Breeze (SB) conditions. It is a complex terrain island with two main mountain ranges (at the north and east) and an elevated area in its center, which defines three main basins: Palma in the west, Alcudia in the northeast and Campos in the southwest.

The physical mechanisms that take place under SB conditions are analysed through the inspection of data from automatic weather stations (AWS) from the Spanish Meteorological Agency (AEMET) during the period 2009–2021. Hourly satellite-derived land-surface and sea-surface temperatures (LST and SST, respectively) are used to compute the surface temperature difference (LST–SST) in the three basins. Besides, a method (Grau et al, 2020) is taken to select the SB events separately in the three basins using data from AWS during the warm months of the year (from April to September).

Results show that the surface temperature difference changes in the three basins pointing that other physical mechanisms are present during SB conditions. For instance, it is explored the role of the large-scale winds in the strength of the SB, the influence of the shape of the basin in the propagation of the SB front and the importance of the vertical temperature gradient (T850hPa – LST) for the SB initiation. It is found that there are differences in the SB features of the three basins (maximum wind speed, initiation and duration of the SB, strength of the horizontal thermal gradient) and SB conditions are not simultaneously met. Besides, interactions between SB and locally-generated winds at the slopes that close the basins are important and they can enhance/diminish the wind locally.

How to cite: Grau Ferrer, A. and Jiménez, M. A.: Statistical characterization of the physical mechanisms under Sea Breeze conditions in a complex terrain island, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12350, https://doi.org/10.5194/egusphere-egu22-12350, 2022.

Fabienne Lohou et al.

The Global Energy and Water cycle Exchanges and World Climate Research Program have pointed out the importance of the land-atmosphere (L-A) coupling for weather and climate models. The Working Group on Numerical Experimentation survey on systematic errors established that the outstanding errors in the modelling of surface fluxes of momentum and sensible and latent heat is the second most important issue. Earth System Models (ESM) and Numerical Weather Prediction (NWP) systems often have large biases in their representation of surface-atmosphere fluxes when compared to observations. The detailed quantification and reduction of these biases are still on-going efforts in many modelling centres. The Models and Observations for Surface-Atmosphere Interactions (MOSAI) project aims at contributing to this effort.

The first step to achieve this objective is to conduct a fair and correct evaluation of the L-A interactions simulated by ESM and NWP models. This is based on (1) reliable references against which the simulated L-A exchanges can be evaluated, and (2) relevant comparison methods able to point out the ESM and NWP system weaknesses. These points define the two first scientific objectives of MOSAI project. The first scientific objective is to investigate and determine the uncertainty and representativeness of L-A exchanges measured over heterogeneous landscapes. Three one-year campaigns are planned to document this heterogeneity on three of the ACTRIS instrumented sites in France. The objective is to make these permanent fluxes measurements well documented in terms of uncertainty, surface energy imbalance and surface heterogeneity representativeness at the scale of the model grid-mesh. The second scientific objective is to propose and test two methods to evaluate the L-A exchanges in ESM using long-term measurements. The first approach is based on sensitivity studies performed with 3D models or with their corresponding single-column version, either forced by data from the MOSAI one-year campaigns or coupled with their LSM, and for which an atmospheric forcing will be derived from operational analyses. The second approach relies on Artificial Intelligence methods (Neural Network or Random Forest) to test the dependency of the surface fluxes to several meteorological variables, at the same time for observation and models. These two methods will allow identifying specific weaknesses of each model at different spatial and time scales.

The second step of the project concerns the improvement of the L-A exchanges simulated by ESM and NWP systems. The coupling between land surface models (LSM) and atmospheric models is based on several simplifications which are different when considering Large-Eddy Simulation (LES), weather or climate models. The third scientific objective of MOSAI project addresses some of these underlying simplifications in the coupling between LSM and atmospheric models, and their impacts on the simulated L-A exchanges. After determining the importance of a realistic heterogeneous landscape versus percentages of unified landscape to correctly simulate the surface flux in ESM and NWP, differential treatment of the boundary-layer parameterizations will be developed, so that the atmosphere model can describe as many sub-columns as the number of land-surface patches to explicitly represent the L-A coupling.

How to cite: Lohou, F., Lothon, M., Bastin, S., Brut, A., Canut, G., Cheruy, F., Couvreux, F., Cohard, J.-M., Darrozes, J., Dupont, J.-C., Lafont, S., Roehrig, R., and Román-Cascón, C. and the MOSAI Team: Model and Observation for Surface Atmosphere Interactions (MOSAI) project, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8797, https://doi.org/10.5194/egusphere-egu22-8797, 2022.

Mon, 23 May, 10:20–11:50

Chairpersons: Maria Antonia Jimenez Cortes, Carlos Yagüe

Aaron Boone et al.

It is known that irrigation can impact the local atmospheric boundary layer characteristics, thereby modifying near surface atmospheric conditions within and downwind of irrigated areas and potentially the recycling of precipitation. The understanding of the impact of anthropization and its representation in models have been inhibited due to a lack of consistent and extensive observations, but in recent years, land surface and atmospheric observation capabilities have advanced. The overall objective of the Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment (LIAISE) project is to improve the understanding and prediction of land-atmosphere-hydrology interactions in a semi-arid region characterized by strong surface heterogeneity between the natural landscape and intensive agriculture. The study region is located over the Pla d’Urgell region within the Ebro basin in NE Spain. This area was selected since it is a breadbasket region: there are discussions underway to further expand this irrigated zone owing to its economic importance, but consensus of current climate projections predicts a significant warming and drying over this region in upcoming years. Thus there is an urgent need to improve the prediction of the potential changes to the regional water cycle since water resources are limited.


Here we present an overview of the intense phase of the LIAISE observational campaign, which is part of the HYdrological cycles in the Mediterranean Experiment (HyMeX) phase 2, that took place in July, 2021 when land surface heterogeneity was at a maximum. A network of 7 stations provided continuous measurements of the surface energy and water budget components for multiple representative land cover types, including irrigated surfaces, along with detailed surface biophysical measurements from the leaf to field scale. Surface fluxes at the field scale were made using scintillometer configurations over 3 of the sites. Lower atmospheric measurements were obtained from tethered balloons, lidar, UHF profilers, frequent radio-sounding releases, UAVs and several aircraft. Finally, airborne instruments measured solar induced florescence, surface temperature over several spectral bands and soil moisture over a transect cutting across the rain-fed and irrigated areas. The main outcome of this project is to provide the underpinnings for improved models leading to better water resource impact studies for both the present and under future climate change.

How to cite: Boone, A., Best, M., Bellvert, J., Brooke, J., Canut-Rocafort, G., Cuxart, J., Hartogensis, O., Ramon Miro, J., LeMoigne, P., Polcher, J., Price, J., and Quintana Segui, P.: Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment (LIAISE) Project: Overview of the Field Campaign intense phase, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8028, https://doi.org/10.5194/egusphere-egu22-8028, 2022.

Naseem Ali et al.

Turbulence in the atmospheric boundary layer (ABL) plays an important role in the weather and climate system as it governs the meteorological exchanges of momentum, energy, and moisture between the free atmosphere and the Earth’s surface. Motivated by the need for conceptual physics-based models that parameterize turbulence in the ABL in terms of spectra at all spatio-temporal scales, we explore a linear random advection approach to characterize different scenarios of sheared convective boundary layer flows. As a main result, we obtain the wavenumber–frequency spectrum as a product of the wavenumber spectrum and a Gaussian frequency distribution, whose mean and variance are given by the mean advection and random sweeping velocities, respectively. The applicability of the model is evaluated with direct numerical simulations of the mixed layer and entrainment zone for the streamwise and vertical velocity components as well as buoyancy. To obtain a fully analytical formula for the linear random advection approach, we propose using a von-Kàrmàn wavenumber spectrum parameterized by the characteristic convective velocity and length scales. These scales are height-dependent and vary considerably with the relative balance of buoyancy and shear forces. The comparison of the von-Kàrmàn-based model for velocity and buoyancy to simulation results shows that the main features of the measured spectra are captured by the model. 

How to cite: Ali, N., Mellado, J. P., and Wilczek, M.: A Wavenumber–Frequency Spectrum Model for Sheared Convective Atmospheric Boundary Layer Flows, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1432, https://doi.org/10.5194/egusphere-egu22-1432, 2022.

Cedrick Ansorge and Hauke Wurps

The profiles of wind speed and direction in turbulent Ekman flow are formulated based on asymptotic theory and data from direct numerical simulation. The profile of the streamwise component follows the classical viscous, logarithmic and wake scaling. In the outer layer, the velocity component profiles can be described by an Ekman-spiral with adapted boundary conditions that result in a reduction of the spiral-like rotation. The span-wise component poses a conceptual challenge to the channel-flow analogy in the context of asymptotic matching; it exhibits a mixed scaling in the surface layer, but follows outer scaling for most of the outer layer. Viscous stress scales universally across the boundary layer in inner units while the total stress becomes universal as a function of outer height. This implies a mixed scaling for the turbulent stress and eddy viscosity across the inner layer and convergence to a universal scaling as function of the outer height across the outer layer for increasing scale separation vide Reynolds numbers.

How to cite: Ansorge, C. and Wurps, H.: Wind veer and wind speed in turbulent Ekman flow, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7575, https://doi.org/10.5194/egusphere-egu22-7575, 2022.

Marta Waclawczyk et al.

In this work we show how to retrieve information about temporal changes of turbulence in the atmosphere based on in-situ wind velocity measurements. The performance of our method is illustrated with the use of high-resolution data taken by a helicopter-borne platform ACTOS (Airborne Cloud Turbulence Observation System) in stratocumulus-topped boundary layer (STBL).

Atmospheric turbulence is a complex phenomenon, characterized by the presence of a plethora of scales (eddies). Turbulence may undergo large space and time variations due to rapidly changing external conditions, it may be locally suppressed or enhanced. To describe characteristic features of turbulence, statistical theories are sought for. In this context, a number of recent research works address the problem of the equilibrium Taylor’s law and its failure in the presence of rapid changes of the system. A new, non-classical, although universal scaling is introduced to describe the latter.

In this work we calculate two non-dimensional indicators, the dissipation factor and the integral-to-Taylor scale ratio and study their dependence on the Taylor-based Reynolds number. By analysing these results we can identify regions where turbulence is in its stationary state, with production balancing the dissipation and regions where turbulence decays in time or, on the contrary, becomes stronger. We also detect non-equlibrium turbulence states which indicate the presence of rapidly-changing external conditions. In this case the investigated statistics do not follow the equilibrium Taylor’s law, but both, the dissipation factor and the integral-to-Taylor scale ratio become inversly proportional to the Taylor-based Reynolds number. 

The presence of non-equilibrium turbulence in the atmospheric boundary layer has important implications, as it indicates that common turbulence closures may fail to predict the dynamics of such systems correctly.  Incorporating non-equilibrium effects to turbulence models may largely improve their predictions.

How to cite: Waclawczyk, M., Nowak, J. L., and Malinowski, S. P.: Detecting non-equilibrium states in atmospheric turbulence., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4965, https://doi.org/10.5194/egusphere-egu22-4965, 2022.

Georgios Bagiatis et al.

The Kolmogorov hypothesis of local isotropy is fundamental in stochastic models of turbulence and generally assumed to hold for atmospheric turbulence. According to Kolmogorov’s second similarity hypothesis, there is a range of turbulent scales (inertial subrange) that are statistically isotropic and the statistics of these scales have a universal form that is uniquely determined by the TKE dissipation rate. Recent work based on atmospheric turbulence measurements has shown that the scale-wise route turbulence takes to reach isotropy at these smallest scales is uniquely determined by the anisotropy of the energy containing eddies.

In this study we explore the connection between large-scale anisotropy and the route to small-scale isotropy through direct numerical simulations (DNS). We perform simulations of neutral flow over flat and rough (wavy) surfaces at different Reynolds numbers, to investigate the scale-wise anisotropy as a function of height from the surface and surface-roughness. The resulting trajectories of relaxation to isotropy are compared to the experimental ones and the differences between the two are explored in light of the return-to-isotropy terms and Reynolds number.

How to cite: Bagiatis, G., Medvedova, A., Stiperski, I., Rotach, M., and Kendl, A.: Scale-wise relaxation to isotropy in direct numerical simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4189, https://doi.org/10.5194/egusphere-egu22-4189, 2022.

Daniela Cava et al.

Observations of the vertical structure of the turbulent flow in different stability regimes above and within the Amazon Forest at the Amazon Tall Tower Observatory (ATTO) site are presented. The shear length scale at the canopy top together with the coherent turbulent structures time and separation length scale were evaluated to determine influence of stability on the inception and development of the roughness sublayer. Five stability regimes were identified. The definition of an intense table regime allowed the identification of a peculiar condition characterized by low-wind and weak coherent structures confined close to the canopy top and producing negligible transport. Submeso motions dominate the flow dynamics in this regime both above and inside the roughness sublayer.

The shear length scale increases with decreasing stability, presenting two asymptotes for large unstable and stable stratification and a linear behaviour close to neutral stratification. The coherent structure time and length scales are detected using an original method based on the autocorrelation functions of 5-min subsets of turbulent quantities. The vertical time scale is larger in neutral conditions and decreases for both increasing and decreasing stability, while the separation length scale at the canopy top presents a linear dependence on the shear length scale, whose slope is maximum in neutral conditions and decreases departing from neutrality. A new parameterization describing the dependence of the coherent eddies’ separation length scale on the h/L stability parameter is presented.

How to cite: Cava, D., Mortarini, L., Quaresma Dias Júnior, C., Brondani, D., Acevedo, O., Oliveira, P., Giostra, U., Manzi, A. O., Araújo, A., Tsokankunku, A., and Sörgel, M.: Impact of Atmospheric Stability on Vertical Propagation of Submeso and Coherent Structure in a Dense Amazon Forest, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7042, https://doi.org/10.5194/egusphere-egu22-7042, 2022.

Miroslaw Zimnoch et al.

Urban areas, which constitute 2% of the land surface, are responsible for around. 70% of anthropogenic CO2 emissions. Estimation of the anthropogenic contribution in total atmospheric CO2 load observed in cities is crucial for better understanding of the human influence on the carbon cycle and can help improve and validate atmospheric models dedicated for such regions.

In 2021, diurnal measurement campaigns were performed with approximately monthly resolution aimed at characterization of vertical profiles of CO2 over the urban area of Krakow, Southern Poland, using a tethered touristic balloon located in the city center. The measurements were conducted up to the altitude of 280 m a.g.l. Simultaneously,  spot air samples were collected in order to determine the contribution of anthropogenic component based on radiocarbon analysis. Based on preliminary results presented in this work, the temporal evolution of the nocturnal (NBL) and convective (CBL) boundary layer over the city can be observed. Part of the profiles also shows CO2 plums detected at the elevation of ca. 200 m a.g.l. originating potentially from nearby industrial emission sources. The model analysis performed using the HySplit model enabled to identify a potential emission source.

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: Zimnoch, M., Sekula, P., Skiba, A., Maslouski, M., Jasek-Kaminska, A., Gorczyca, Z., Chmura, L., Bartyzel, J., Necki, J., and Jagoda, P.: Vertical profiles of CO2 concentration in the urban area of Krakow, Poland – preliminary results of CoCO2 measurement campaigns., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12270, https://doi.org/10.5194/egusphere-egu22-12270, 2022.

Gianluca Pappaccogli et al.

In the last decades, ecosystem activities are continuously monitored at long-term eddy covariance (EC) research infrastructures located worldwide, in order to estimate turbulent exchanges at the land-atmosphere interface, which plays a key role in many applications. In this context, the eddy covariance technique represents the reference method for the estimation of direct aerosol turbulent exchanges. In this study, the performance of Linear Detrending (LDT) and a Recursive Digital Filter (RDF) in removing the low-frequency contribution to the calculations of aerosol vertical turbulent fluxes is investigated. The both methods are applied in order to obtain a correct evaluation of ultrafine particles, exchange velocity, separating the negative cases (named emission velocity - Ve) from positive cases (the so called deposition velocity - Vd). An ogive analysis of turbulent fluxes was carried out in order to obtain the low-frequency time scales (τc) required by the RDF for different atmospheric stability conditions (i.e. unstable, stable and neutral). RDF was applied also with a constant low-frequency time scale (RDF300, τc=300s). In this comparison study LDT has been used as method of reference. Stationarity test proposed by Mahrt (1998 - MST98) has been applied particle number fluxes with and without applying LDT and RDF methods, in order to investigate the impact of separation criteria on stationarity test performances. The novelty of this work consists in the straightforward application of the recursive digital filter to real long-case EC measurement of particle number concentration flux, assessing the performance of the two filtering methodologies, which can be applied in real-time and post-processing automated procedures. Results show that there are no significant differences in stationary cases for filtering procedures. The sensitivity analysis carried out for the main turbulent parameters highlights that wider discrepancies occur between LDT and RDF300, showing a large increase in turbulent number particles flux.  Filtering procedures lead a slight increase of exchange velocity, although and underestimation occurs for emission and deposition velocities. The filtering effect of RDF manuscript strongly depends on the low-frequency time scale, which should be preferably estimated by means of spectral criteria.

How to cite: Pappaccogli, G., Donateo, A., and Famulari, D.: A comparison study between linear detrending and recursive digital filter in aerosol deposition velocity evaluation by eddy covariance method , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2521, https://doi.org/10.5194/egusphere-egu22-2521, 2022.

Stephanie Reilly et al.

The most frequently used turbulence parameterizations in numerical weather prediction (NWP) and general circulation (GC) models are turbulence schemes with a prognostic turbulence kinetic energy (TKE). These turbulence schemes are strongly dependent on an ad-hoc quantity, the turbulence length scale. The turbulence length scale is used to parameterize the molecular dissipation of TKE and is also required for calculating the turbulence exchange coefficients. Traditionally, the turbulence length scale formulations do not take into account the transfer of TKE across scales, as they are designed for scales above the energy production range of the turbulence spectra. However, with computational power growing, it has become increasingly possible to simulate at scales within the energy production range, that is within the gray zone of turbulence. At resolutions within the gray zone, the cross-scale transfer of TKE needs to be taken into account in order to accurately represent the turbulence. For this purpose, a turbulence length scale diagnostic was developed that can be used for resolutions in the gray zone. This is achieved by calculating the turbulence length scale from the so-called effective dissipation rate, a combination of the cross-scale TKE transfer and the dissipation rate. The effective dissipation rate is estimated from the budget of the TKE using large-eddy simulation (LES) data. A similar approach can be used to calculate turbulence length scale from the budgets of scalar variances. This study makes use of three different turbulence length scale diagnostics based on: the TKE, the variance of the total specific water content, and the variance of the liquid water potential temperature. Four algebraic turbulence length scale formulations are evaluated using the turbulence length scale diagnostics as a reference. The evaluation of the algebraic turbulence length scale formulations is conducted for several idealized LES cases, simulated using the MicroHH model. These LES cases represent a variety of different atmospheric boundary layer conditions.

How to cite: Reilly, S., Bastak Duran, I., Theethai-Jacob, A., and Schmidli, J.: An Evaluation of Algebraic Turbulence Length Scale Formulations using Budget-Based Diagnostics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8623, https://doi.org/10.5194/egusphere-egu22-8623, 2022.

Yi Lin et al.

The boundary-layer low-level jet (LLJ) is a widespread wind phenomenon that can strongly affect urban heat islands (UHIs). However, the influence of LLJ on the three-dimensional structure of UHI remains poorly understood. Thus, in this study, we focused on the impacts of boundary-layer LLJs on the horizontal distribution, vertical development, and three-dimensional structure of UHIs. Observational data for the surface values of meteorological parameters were collected from 376 automatic weather stations (AWSs) in Beijing and its surrounding areas. Vertical profiles of the atmospheric boundary layer were also obtained from a field sounding campaign conducted in Beijing from August 28 to September 2, 2016. In addition, we also performed three-dimensional model simulations using the Weather Research and Forecasting (WRF) model to capture the change of meteorological parameters. The conclusions achieved in the present study are as follows:

(1) When a LLJ occurs in Beijing, the Richardson number Ri was found to be smaller than 0.25 at all these urban and suburban stations. As Ri represents the stability of the whole atmosphere, it can indicate the influence of upper winds on the horizontal distribution of the canopy UHI. When Ri<0.25 and LLJ occurs, the momentum is transmitted downwards, leading to the increase of the wind speed near the ground. This enlarged wind speed would carry the heat from urban areas downwards to the suburban regions, resulting in a downwind drift of the canopy UHI position and a expansion of the UHI area by approximately 1,000 km2. (2) It was also found that when a LLJ occurs, the vertical mixing above the urban area is enhanced, with a TKE up to 0.52 m2/s2 near the ground. This enhanced vertical mixing causes a decrease in the lapse rate of the temperature in the urban area. The lapse rate when LLJ presents (0.3°C/100m) is less than half of that when LLJ is absent (0.7°C/100m). Under this condition, the height of the heat island also elevates up to approximately 200m. (3) We found that the LLJ is capable of increasing the temperature of the downwind urban area by a maximum of 8.5°C/h through the warm advection. The temperature advection in the upper air caused by LLJ also tilted the three-dimensional structure of UHI. As a result, the heat island behaves as a plume under the influence of LLJ.

How to cite: Lin, Y., Wang, C., and Cao, L.: Impact of the boundary-layer low-level jet on the three-dimensional structure of the urban heat island in Beijing, China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-160, https://doi.org/10.5194/egusphere-egu22-160, 2022.

Juerg Schmidli et al.

The unified parameterization of turbulence and clouds in the atmospheric boundary layer is one of the challenges in current weather and climate models. An update of the two-energy turbulence scheme is presented, the 2TE+APDF scheme. The original version of the two-energy scheme is able to successfully model shallow convection without the need of an additional parameterization for non-local fluxes. However, the performance of the two-energy scheme is worse in stratocumulus cases, where it tends to overestimate the erosion of the stable layers. To alleviate this problem, we propose several modifications: an update of the stability parameter to consider local stratification, a more flexible computation of the turbulence length scale, and the introduction of the entropy potential temperature to distinguish between a shallow convection and a stratocumulus regime. In addition, the two-energy scheme is coupled to a simplified assumed PDF method in order to achieve a more universal representation of the cloudy regimes. The updated turbulence scheme is evaluated for several idealized cases and one selected real case in the ICON modeling framework. The results show that the updated scheme corrects the overmixing problem in the stratocumulus cases. The performance of the updated scheme is comparable to the operational setup of the ICON model, and can be thus used instead of the operational turbulence and shallow convection scheme in ICON. Additionally, the updated scheme improves the coupling with dynamics, which is beneficial for the modeling of coherent flow structures in the ABL, such as, for example, cloud streets.

How to cite: Schmidli, J., Bašták Ďurán, I., and Sakradzija, M.: Unified parameterization of turbulence and boundary layer clouds using the updated two-energies turbulence scheme , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7028, https://doi.org/10.5194/egusphere-egu22-7028, 2022.

Mon, 23 May, 13:20–14:50

Chairpersons: Maria Antonia Jimenez Cortes, Carlos Yagüe

David Avisar and Sigalit Berkovic

Jerusalem (Jer, Israel) is located on a mountain (~800m above sea-level), between the Eastern Mediterranean coast, to the west, and the Jordan valley (~400m below sea-level), to the east. This coast—mountain—valley (iCMV) complex terrain structure has a relatively smooth contour line. Nevertheless, the corresponding boundary layer dynamics (BLD) has not yet been fully unraveled for the summer season, which is characterized by a persistent synoptic regime. In this work we use the Weather Research and Forecasting (WRF) model, together with ceilometer measurements, to decipher the detailed mesoscale evolution of the iCMV BL during the late summer period of Sep. 5-15, 2017, where the maximal BL depth in Jer vary in the range 500-1500m. We first validate the BL height (BLH) simulated by 4 WRF BL parameterizations. Accordingly, the MAE is around 120m and 180m for the coastal and Jer areas, respectively. An analysis of the modeled daytime iCMV BL evolution shows that the topography, sea-breeze, and the synoptic regime conspire to produce the following pattern: In the morning, the topography and the radiation forcing induce a surface-flow-convergence (SurFCon), above which the BLH is locally elevated. The initial SurFCon position, relative to Jer, depends on the synoptic flow. Afterwards, as the sea-breeze propagates inland, it advects the SurFCon eastward. The locally-elevated BLH collapses in the late afternoons when it reaches the valley. Generally, the weaker, or easterly, the synoptic flow is, the more likely the initial location of the elevated BLH (SurFCon) will be west to Jer, and during noontime it will pass through Jer, which probably experiences a higher daily maximum BLH. On the other hand, during a westerly synoptic flow the SurFCon is located east to Jer at all times. Thus, the city experiences relatively lower daily maximum BLH, in contrast to the coastal plains.  Furthermore, we conclude that the surface synoptic classification cannot serve as a BLH predictor for Jer. This conclusion should be validated for BLD throughout the year.

How to cite: Avisar, D. and Berkovic, S.: High Spatiotemporal Resolution Planetary Boundary Layer Dynamics Across the Israeli Coast—Mountain—Valley Terrain Unraveled by WRF Simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-646, https://doi.org/10.5194/egusphere-egu22-646, 2022.

Lukáš Bartík et al.

Uncertainties associated with the determination of model vertical turbulent diffusion profiles are generally considered to be one of the main causes of the discrepancies between modeled and measured pollutant concentrations. In this work, we performed four two-year long offline simulations, specifically for the period 2018–2019, using the WRF-CAMx model system over Central Europe with a horizontal resolution of 9 km x 9 km in which we used various methods of calculation of vertical turbulent diffusion coefficients (based on WRF meteorology) while the other meteorological fields we kept the same. Further, we analyzed the effects of these perturbations on spatio-temporal changes in concentrations of some components of the fine fraction of inorganic aerosols (ammonium, sulfates and nitrates) and their gaseous precursors (ammonia, NOx, sulfur dioxide). We also validated the surface concentrations of the mentioned pollutants using the AirBase and EMEP datasets.

How to cite: Bartík, L., Liaskoni, M., and Huszar, P.: Study of the influence of various vertical turbulent diffusion profiles on the concentrations of secondary inorganic aerosol and their gas precursors over Central Europe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1296, https://doi.org/10.5194/egusphere-egu22-1296, 2022.

Bas Van de Wiel et al.

Heat transport through short and closed vegetation, such as, grass is modelled by a

simple diffusion process. The grass is treated as a homogeneous ``sponge layer'' with

uniform thermal diffusivity and conductivity, placed on top of the soil. The temperature

and heat flux dynamics in both vegetation and soil are described using harmonic

analysis. All thermal properties have been determined by optimization against

observations from the Haarweg station in the Netherlands. Our results

indicate that both phase and amplitude of soil temperatures can be accurately

reproduced from the vegetation surface temperature. The diffusion approach requires

no specific tuning to, e.g., the daily cycle, but instead responds to all frequencies

present in the input data, including quick changes in cloud cover and day-night

transitions. The newly determined heat flux at the atmosphere-vegetation interface is

compared with the other components of the surface energy balance. The budget is

well-closed, particularly in the most challenging cases with varying cloud cover and

during transition periods. We conclude that the diffusion approach is a promising and

physically consistent alternative to more ad-hoc methods, like ``skin resistance''

approaches for vegetation and bulk correction methods for upper soil heat storage.

However, more work is needed to evaluate parameter variability and robustness under

different climatological conditions. From a numerical perspective, the multi-frequency

description allows for studying cases where the atmospheric boundary layer and the

top-surface interact on sub-hourly timescales. It would therefore be interesting to

couple the current land-surface description to turbulent resolving methods, such as,

large-eddy simulations.

How to cite: Van de Wiel, B., van der linden, S., Kruis, M., Hartogensis, O., Moene, A., and Bosveld, F.: Heat Transfer through Grass: A Diffusive Approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8030, https://doi.org/10.5194/egusphere-egu22-8030, 2022.

Carlos Román-Cascón et al.

The effects of the land-cover (LC) type on the surface fluxes have been investigated using observational data and numerical weather prediction models in numerous studies. Most of these works stress the need for a realistic and accurate representation of the LC within the models, including appropriate soil and vegetation parameters. This is needed to obtain more realistic near-surface atmospheric processes, leading to better forecasts of atmospheric variables of common interest (2-m temperature, 10-m wind speed, relative humidity, etc.). In a previous work, we have studied these effects focusing on a fair-weather day in a heterogeneous area of southern France. To this aim, we used the Weather Research and Forecasting (WRF) model at 1 km with an improved (30-m and more realistic) representation of the LC, configured with four land surface models (LSM): Noah, Noah-MP, CLM4 and RUC.

The results showed that the influence of LC on surface fluxes were important but differed depending on the LSM, displaying some extreme flux values for specific LC categories (e.g., urban and conifer). This opened the question of how these effects impacted the development of the atmospheric boundary layer (ABL), which motivated the present work. To this aim, we analysed the ABL height (zi) simulated by WRF in each LC category using the different LSM. These values were compared to those observed with multiple instrumentation (radiosoundings, unmanned aerial vehicles, wind profilers, etc.) available during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign, which took place in the area of study in summer 2011.

The zi simulated values were similar in magnitude and in temporal evolution than those observed, indicating a good performance of the model for the 4 LSMs. However, some LSM displayed a higher variability in the simulated zi depending on the sensible/latent heat partitioning and on the type of LC. These results indicate that the important effects of the LC type on the surface fluxes are transferred to the top of the PBL, affecting zi even from an analysis of this variable at a model resolution of 1x1 km.

In order to disentangle whether the spatial variability of the modelled zi is close to the reality, for future works we highlight the importance of intensive and frequent zi measurements at the field over different nearby sites with contrasting LC. This will help to continue understanding how the surface forcing affects the PBL development and to what extent the processes reproduced in the model differ from those observed in the reality.

How to cite: Román-Cascón, C., Lothon, M., Lohou, F., Hartogensis, O., Vila-Guerau de Arellano, J., Pino, D., Yagüe, C., and Pardyjak, E.: Analysis of the land cover impact on boundary layer height from WRF and BLLAST data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5253, https://doi.org/10.5194/egusphere-egu22-5253, 2022.

Sofia Farina et al.

An Eulerian model for the dispersion of a passive tracer over a simplified slope driven by a thermally driven circulation is presented here. The source of the tracer is point-like and the emission continuous, the local circulation is a pure anabatic flow modelled following Prandtl’s (1942) steady-state model. The eddy diffusivity is considered constant along the vertical direction. The incapability of a classical Gaussian model to forecast the concentration field is shown through a comparison between the results of the Gaussian and Eulerian models. A study of the sensitivity of the concentration field to the position of the source and to the characteristics of the wind field is proposed. Moreover, a relationship between the position and the intensity of the ground concentration field, together with its dependence on the environmental parameters is found. 

Prandtl L. 1942. Führer durch die Strömungslehre, Chapter 5. Vieweg und Sohn: Braunschweig, Germany. [English translation: Prandtl L. 1952. Mountain and valley winds in stratified air, in Essentials of Fluid Dynamics: 422–425. Hafner Publishing Company: New York, NY]


How to cite: Farina, S., Bisignano, A., and Zardi, D.: Numerical modelling of passive tracer dispersion from a continuous point source in a steady thermally driven slope wind, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4122, https://doi.org/10.5194/egusphere-egu22-4122, 2022.

Ekaterina Tkachenko et al.

Various types of one-dimensional RANS (Reynolds-Averaged Navier-Stokes) parametrizations are widely used in modern weather and climate models for replicating atmospheric boundary layer (ABL) dynamics. RANS models can accurately reproduce states of ABL close to stationary [1,2], but fail to model the ABL diurnal cycle and other non-stationary processes with similar accuracy[3]. Therefore, one of the purposes of studying non-stationary states of the ABL is using the information about the processes that govern such ABL states for the improvement of RANS models.

This study focuses on the evening transition, which is a part of the ABL diurnal cycle. During this transition, the decay of turbulent kinetic energy (TKE) takes place. Results of large-eddy simulation (LES) experiments where the evening transition is modeled, both sheared and shear-free cases, are presented. The TKE balance between components is analyzed. It is shown that the transition can be broken down into well-pronounced periods of fast and slow TKE decay. TKE anisotropy within these two periods is studied, where the destruction of the large part of TKE due to thermals inertial movement is observed during the fast decay period. This is followed by the redistribution of the energy into horizontal components, which results in the formation of quasi-horizontal turbulence, with TKE decay, in comparison to the isotropic state, slowing down significantly. Finally, the distribution of TKE between large- and small-scale eddies is analyzed, both within the entire ABL domain and at certain heights.

The results are then compared to those obtained in one-dimensional boundary layer model, where k-ε closure is utilized for the parametrization of turbulent diffusion, and it is shown that the latter fails to reproduce evening transition dynamics properly, at least in part due to gradient approximation of turbulent fluxes. The choice of the k-ε closure results in decreased TKE decay rate during the fast decay period and increased rate during the slow decay period, which may be due to the TKE dissipation equation inclusion in the model. Therefore, possible approaches towards modification of RANS closures aimed at correct modeling of ABL non-stationary dynamics are explored.

This study was funded by Russian Foundation of Basic Research within the project #20-05-00776.

1. Debolskiy A., Mortikov E., Glazunov A. and Lüpkes C., 2021. Evaluation of surface layer stability functions and their extension to first order turbulent closures for weakly and strongly stratified stable boundary layer. Boundary-Layer Meteorology, Under review.
2. Mortikov, E.V., Glazunov, A.V., Debolskiy, A.V., Lykosov, V.N. and Zilitinkevich, S.S., 2019. On the modelling of the dissipation rate of turbulent kinetic energy. Doklady Akademii Nauk, 489(4), pp. 414-418.
3. Svensson, G., Holtslag, A.A.M., Kumar, V., Mauritsen, T., Steeneveld G.J., Angevine W.M., Bazile E., Beljaars A., de Bruijn E.I.F., Cheng A., Conangla L., Cuxart J., Ek M., Falk M.J., Freedman F., Kitagawa H., Larson V.E., Lock A., Mailhot J., Masson V., Park S., Pleim J., Söderberg S., Weng W., Zampieri M., 2011. Evaluation of the diurnal cycle in the atmospheric boundary layer over land as represented by a variety of single-column models: The second GABLS experiment. Boundary-Layer Meteorology, 140(2), pp.177-206.

How to cite: Tkachenko, E., Debolskiy, A., and Mortikov, E.: Large-eddy simulation and parametrization of turbulence decay in atmospheric boundary layer, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12569, https://doi.org/10.5194/egusphere-egu22-12569, 2022.

Jonathan Kostelecky and Cedrick Ansorge

Direct numerical simulation (DNS) of the atmospheric boundary layer (ABL) is becoming more and more popular for its conceptual simplicity and increasing degree of realism: domain sizes and simulation durations can be attained that allow for extrapolation of results to the geophysical limit. Geophysical flows predominantly occur over rough surfaces, which significantly affects drag, mixing and transport properties of the flow. For such flows, a method is needed that allows one to impose the intricate mechanical boundary condition resulting from a rough wall, while maintaining the efficient and tuned numerical methods for Cartesian meshes. This is achieved by an immersed boundary method (IBM), where three-dimensional roughness elements are fully resolved at the bottom wall of the simulation domain. Based on the work by Laizet and Lamballais (J. Comp. Phys 2009, Vol 228, p.5989-6015), we develop an IBM for efficient use in a stratified environment. First, a spline interpolation method is used to reduce oscillations in the artificial part of the velocity field. Second, a partially staggered arrangement is introduced to avoid spurious pressure oscillations, as is the case with collocated grids for pressure and velocity. Third, the thermal boundary conditions need to be adjusted to account for background gradients across the height of roughness elements. Based on this implementation, the effect of roughness is investigated in terms of fully resolved three-dimensional roughness elements located on the bottom wall of the simulation domain for neutral and stably stratified turbulent Ekman layer flows.

* This work is funded by the ERC Starting Grant ”Turbulence-Resolving Approaches of the Intermittently Turbulent Atmospheric Boundary Layer [trainABL]” of the European Research Council (funding ID 851347).

How to cite: Kostelecky, J. and Ansorge, C.: Direct Numerical Simulation of the Aerodynamically Rough Atmospheric Boundary Layer – Implementation of an Immersed Boundary Method for Turbulent Ekman Flow, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9463, https://doi.org/10.5194/egusphere-egu22-9463, 2022.

Prabhakar Namdev et al.

   In the present study, an effort has been made to investigate the performance of two planetary boundary layer (PBL) schemes available in the NCAR-CAM5 climate model. The available schemes are the Holtslag and Boville (HB) scheme and the University of Washington (UW) scheme. The HB scheme considers surface heating because of incoming solar radiation to be the origin of turbulent motion in the PBL. However, the UW scheme is a 1.5-order local TKE (turbulent kinetic energy) closure scheme. It considers the increased turbulent activity region associated with the buoyancy perturbations because of the cloud-top entrainment instability and longwave cooling present at the stratocumulus-topped PBLs.

   The evaluation was carried out by conducting two simulations with the NCAR-CAM5 climate model over six years using HB and UW PBL schemes with a horizontal resolution of 1o. The last five years of the simulation are used in the analysis, discarding the first year as spin-up. The study evaluates the performance of two PBL schemes during the DJF (December–January), MAM (March–May), JJA (June–August), and SON (September–November) seasons over different climatic zones that exist within Indian land. The study reveals that the spatial distribution of sensible and latent heat fluxes, 2-m temperature, wind speed at 925 hPa and 200 hPa, and precipitation produced by both the schemes are consistent with ERA-interim reanalysis data. The UW scheme, when compared to the HB scheme, shows significant heating over the South Indian region during all seasons except DJF. It significantly reduced the cold bias present over the South Indian region. The UW scheme is favorable for simulating precipitation over central and north-east India, mostly during JJA. However, it significantly increased the positive bias over the western ghats and the north and south Indian regions during JJA. It also increased the positive bias over south India during SON. Both the schemes performed almost similar for precipitation during DJF and MAM. In case of sensible and latent heat fluxes, both the schemes have a more or less similar distribution of biases in all the seasons, with a slight difference in magnitude. As far as wind is concerned, both the schemes use a reasonable approach to the positioning of jets and observed monsoon flow with a slight difference. The UW scheme significantly reduced the existing negative bias in the HB scheme for wind speed at 925 hPa during JJA. Further, recommendations have been made for the performance of two PBL schemes over different climatic zones within Indian land.


  • Holtslag, A. A. M., and B. A. Boville, Local versus nonlocal boundary-layer diffusion in a global climate model, J. Climate, 6, 1825–1842, 1993.
  • Bretherton, C. S., and S. Park, A new moist turbulence parameterization in the community atmosphere model, J. Climate, 22, 3422–3448, 2009.

Keywords: PBL parameterization, Climate model, surface turbulent fluxes, precipitation

How to cite: Namdev, P., Sharan, M., and Mishra, S. K.: Performance of two planetary boundary layer parameterizations in the NCAR-CAM5 climate model over different climatic zones within Indian land, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11061, https://doi.org/10.5194/egusphere-egu22-11061, 2022.

Julian Quimbayo-Duarte et al.

The response of the boundary layer flow to resolved versus parametrized orographic drag over moderately complex terrain is investigated. The larger terrain scales may trigger propagating gravity waves and generate flow blocking, while the smaller scales (smaller than 5 km) may modify the turbulent boundary layer leading to turbulent orographic form drag (TOFD). We perform high-resolution numerical simulations to evaluate the ability of a TOFD parametrization to reproduce the impact of small-scale orographic features on the flow over complex terrain. The tool selected to perform the simulations is the Icosahedral Nonhydrostatic (ICON) numerical model, a unified modelling system for global numerical weather prediction (NWP) and climate studies. In the present study, the model is used in its limited-area mode. In the TOFD parametrization used for the present simulations, the surface stress and its vertical distribution are formulated in terms of the spectrum of the orography, meaning that it only depends on the orography characteristics in the domain. As a first step simulations using different grid spacings, from the km scale to the 100 m scale, are carried out to reproduce the intensive observational period (IOP) of the Perdigão field experiment. The km-scale simulations in NWP mode are run continuously for the complete 49-day IOP using ERA5 data for initial and boundary conditions. The large-eddy simulations, at O(100 m) grid spacing, are run for selected periods nested into the NWP runs. The initial results of the NWP control simulation show good performance when compared to the tower wind observations for selected periods, but not for the entire IOP. The reasons for the variable performance is investigated.

How to cite: Quimbayo-Duarte, J., Schmidli, J., Köhler, M., and Schlemmer, L.: Analysis of the impacts of small-scale orography on the atmospheric boundary layer.Developing ICON-LES for the Perdigão field experiment., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8818, https://doi.org/10.5194/egusphere-egu22-8818, 2022.

Andrey Debolskiy et al.
Alexander Baklanov and Robert Bornstein

Last year the scientific community lost a great scientist; leader in environmental turbulence and planetary boundary layer research; recipient of the 2019 International Meteorological Organization (IMO) Prize and many other science awards; leader of numerous international research projects; outstanding mentor, and dear friend, Professor Sergej Zilitinkevich.

Among his numerous outstanding scientific achievements in the boundary layer theory, several theoretical results broadly used in the numerical weather prediction, climate, and air pollution modelling communities, in particular, should be mentioned:

  • The Zilitinkevich formula for the depth of stably stratified PBLs is often called that depth scale by Sergej’s name, which indicates that his result is a truly classical one.
  • The Zilitinkevich correction to the rate equation for the depth of a convectively mixed layer, and the resistance and the heat and mass transfer laws for geophysical turbulent flows are also widely known and used.
  • The Zilitinkevich scale - a length scale of a rotational stratification turbulent mixing in stably stratified PBLs.
  • Conceptual models of new types of atmospheric PBLs, i.e.,: conventionally neutral PBLs settled on the background of the strongly stable stratification typical of the free atmosphere are several times thinner than truly neutral PBLs settled in neutral stratification; and long-lived stable PBLs typical in winter time at high latitudes and affected by the stably stratified free atmosphere.
  • Discovered and described by Zilitinkevich: the “weak turbulence regime,” typical of the free atmosphere, which determines the turbulent transport of energy and momentum and the diffusion of passive scalars.
  • Non-local turbulent transport for BLM and the pollution dispersion aspects of the coherent structure of convective flows.

These results have paved the way towards improved theories and parametrizations of boundary layers in many NWP, climate, and ACT models worldwide.
Over the last few decades, Sergej Zilitinkevich was deeply concerned with general questions of the physical nature of geophysical (and astrophysical) turbulence. The classical view, pioneered by Kolmogorov, assumes a cascade process from large eddies towards small eddies and eventually to heat. This “chaos out of order” paradigm put forward for shear-generated non-stratified turbulence is shifted towards an “order out of chaos” paradigm more appropriate for real-world turbulence complicated by body forces, where small-scale motions can organize themselves and give rise to quasi-organized coherent structures at larger scales. Sergej made a remarkable contribution to this paradigm shift. He passionately addressed several fundamental issues, such as the: origin and transport properties of coherent motions, effect of buoyancy on turbulent transport, and maintenance of turbulence at strongly stable stratification. This promising and long-awaited scientific revolution in this area of research will allow for a better understanding of the nature of global pollution and climate change.
In this presentation we analyze the scientific legacy of Sergej Zilitinkevich for further developments in boundary layer research and modelling.

How to cite: Baklanov, A. and Bornstein, R.: Scientific legacy of Sergej Zilitinkevich for boundary layer research and modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12966, https://doi.org/10.5194/egusphere-egu22-12966, 2022.