The Atmospheric Boundary Layer (ABL) is the portion of the troposphere that is directly influenced by the Earth’s surface and responds to combined action of mechanical and thermal forcing. Most of the energy exchange with respect to solar heating and evaporation that drive the atmosphere and the ocean occur within the ABL, yet it is one of the most poorly observed and modeled regions of the atmosphere. Conventional passive microwave systems fall well short of being optimized for near surface sensing due to limited number of spectral channels and coarse spectral resolution covering only a small portion of the spectrum of interest for ABL sensing.

The so called “window regions” of the microwave spectrum between and on the shoulders of the strong oxygen and water vapor absorption lines carry the information on the near surface thermodynamic structure in the boundary layer. Sampling these regions requires new spectrometers capable of resolving >50 GHz spectral regions at modest spectral resolution (~1GHz). The ultra-wideband photonic spectro-radiometer instrument is funded by NASA ESTO under ACT-20 program to combine low-noise wideband RF technology with a novel photonic integrated circuit (PIC) design for obtaining large bandwidth (>50 GHz) with enhanced channel resolution (<1 GHz). A high-speed, low-loss electro-optic modulator is used to convert radio frequency energy into sidebands on an optical carrier, preserving both amplitude and phase of the radiometric signal. The designed PIC includes an input star-coupler that divides the optical power transmitted from the optical modulator among N waveguides monotonically increasing in length within an arrayed waveguide grating (AWG) that provides chromatic dispersion, an output star-coupler that forms an image of the optical spectrum, and an array of photodiodes that convert the optical power to electrical signals. The ultra-wideband 50 GHz direct acquisition spectrometer capability has been successfully tested and validated on the fabricated PIC. The combination of a low-noise wide-band RF radiometer with an RF Photonics backend system is a key technology development allowing unprecedented ability to spectrally resolve the complete microwave spectrum which is critically needed for the planetary boundary layer sensing. In this paper, we will describe the capabilities of this system for measuring the thermodynamic structure in the lower ~2km of the atmosphere.

How to cite: Ogut, M., Brown, S., Misra, S., Kittlaus, E., Kangaslahti, P., Murakowski, J., and Gehl, M.: Atmospheric boundary layer sensing using ultra-wideband photonic microwave spectrometer, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2074, https://doi.org/10.5194/egusphere-egu24-2074, 2024.

The “uRban hEat and pollution iSlands inTerAction in Rome and possible miTigation strategies” (RESTART) is a 2-years project, funded by the Italian Ministry for University and Research as a Project of National Interest (PRIN2022).RESTART aims to explore the interaction between the Urban Heat Island (UHI) and the Urban Pollution Island (UPI) in Rome (Italy),providing a series of mitigation strategies, including tailored Nature-Based Solutions, and ready-to-use guidelines for the improvement of well-being and liveability in urban environments. The connection between UHI and UPI is investigated by inspecting quality-checked datasets of meteorological trace gases and aerosol observations, provided by local and international observatories and dense networks of instruments in Rome.Specifically,the UHI is studied by examining the time series of atmospheric near-surface temperature (average, minimum, maximum daily), relative humidity, pressure, and wind speed, while the UPI is characterised by the observations of trace gases (e.g., NO, NO2, O3, CO), particulate matter (PM10, PM2.5),aerosols optical properties (e.g., aerosol optical depth, AOD, Ångström exponent, single scattering albedo, SSA, particle volume size distribution) in terms of surface and columnar contents and vertical profiles, based on the availability of measurements.The city of Rome (Lat. 41.90 °N, Lon. 12.54 °E) is the most populous and extended Italian city and the third most densely populated metropolis in Europe. Rome is located in the central region of the Italian Peninsula, about 27 km inland from the Tyrrhenian coast. Due to its position in the middle of the Mediterranean Basin and the complex orography of its surroundings, the city is frequently subjected to the advection of Saharan dust in the case of persistent southerly winds, and to the sea breeze regime from the southwest, the latter particularly evident during summertime under anticyclonic conditions. In recent years, the city has experienced significant atmospheric warming and a substantial intensification of extreme weather events, such as heat waves, tropical nights, and droughts.This work explores the connection among some meteorological observations (near-surface temperature and relative humidity) from weather stations, columnar aerosol properties (AOD and SSA) from Skynet and AERONET international networks, and UHI intensities during heat waves, paying particular attention to nighttime. During the selected events, the synoptic weather conditions affecting the interaction between the UHI and the aerosol properties, are discussed.

How to cite: Campanelli, M., Di Bernardino, A., Brattich, E., Argentini, S., Barbano, F., Casasanta, G., Cecilia, A., Di Sabatino, S., Erriu, M., Falasca, S., Maestri, T., and Siani, A. M.: Connection among meteorological observations,columnar aerosol properties and urban heat island during nighttime extreme heat events in the uRban hEat and pollution iSlands inTerAction in Rome and possible miTigation strategies(RESTART)project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1856, https://doi.org/10.5194/egusphere-egu24-1856, 2024.

Turbulence intermittency driven by submeso motions limits the progress of turbulence theory. Field observations from the Horqin Atmospheric Boundary-Layer and Environment Experimental Station, China were used to investigate turbulence intermittency. An automated algorithm to Separate and reconstruct Submeso and Turbulent motions (SST) was improved for more accurately extraction and quantitative characterization of submeso motions. The existing intermittency intensity indices, the local intermittency strength of turbulence (LIST) and intermittency strength (IS), which are based on kinetic energy only, are revised by considering the potential energy of submeso and turbulent motions to quantify intermittency intensity more comprehensively. The analysis of eight cases revealed that turbulent intermittency events are characterized by quiescent (pulsation, material, and energy transportation are weak) and burst (pulsation, material, and energy transportation fluctuate violently) periods. The conversion of both the kinetic and potential energy of submeso to turbulent motion contributes to the transition from quiescent to burst periods. The transition always occurs after ΔTE<0 (the Total Energy difference between the submeso motion and turbulence), followed by a significant increase in ΔTE. Atmospheric stability decreases during the transition from quiescent to burst periods in most cases. In a totally intermittent night, the burst periods take up most of the material and energy transport, and the amount transported is not smaller than that during a totally turbulent night. The weaker the intermittency at night, the greater the capacity of turbulent transport. A comparison of five types of turbulence intermittency intensity indices highlights the consistency and advantages between LIST (IS) and indices in the literature. Finally, we found that turbulent intermittency events tended to occur more easily in atmospheric boundary layer (ABL) with small winds (U<2 m/s) or stable stratification (Rib>1), although they can also occur in ABL with unstable stratification and in the non-stationary state of the day-night transition.

How to cite: Ren, Y. and Zhang, H.: Quantitative description and characteristics of submeso motion and turbulence intermittency, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3266, https://doi.org/10.5194/egusphere-egu24-3266, 2024.

Small uncrewed aerial systems (UAS) are platforms which have been introduced into every-day life within the last decade due to their low cost, good availability and ease of use. They serve a large variety of applications, including aerial photography and cinematography, but also scientific purposes in earth observation. In atmospheric sciences, fixed-wing UAS have been used at first to collect in situ measurements especially in the atmospheric boundary layer (ABL). The way data was collected was based on common know-how from piloted research aircraft. Flow probes and fast-response sensors were installed to measure thermodynamic variables and derive turbulent fluxes. This study focuses on small multicopter UAS which are the most common type of UAS and usually referred to as `drones'. These systems are easier to operate due to their capability of vertical take-off and landing and advanced control systems.
For the most part in atmospheric measurements, multicopter UAS are applied to collect vertical profiles of wind, temperature and humidity. For such profiling tasks, similar sensors as in radiosondes can be deployed and provide a good accuracy for temperature and humidity, but resolving turbulence is usually not the primary focus. However, if multiple systems can be placed at most flexible locations within the ABL to observe thermodynamic features at a high resolution, this enables a variety of new possibilities for research. We show that with the DLR SWUF-3D (simultaneous wind measurement with a UAS fleet in 3D) quadrotor fleet that consists of 35 UAS, turbulence eddies can be resolved with a frequency of up to 2 Hz by the individual drones. This applies for 3D wind measurements as well as for temperature measurements with a newly developed fine-wire platinum resistance thermometer (FWPRT). Within the limits towards the smallest scales we show that the data can be used to calculate fluxes of momentum and sensible heat with reasonable uncertainties in many atmospheric conditions. Additionally to field measurements, the UAS were calibrated and the results were verified in a wind tunnel setup. 
We show how data of the SWUF-3D fleet can be used to calculate spatial correlation and coherence in ABL flow. The system was also used to measure complex flow in an Alpine valley and in the near wake of a wind turbine.  An overview of the applications is given to show the potential of turbulence-resolving, spatio-temporal measurements with a large fleet of multicopter UAS.

How to cite: Wildmann, N., Kistner, J., and Alexa, A.: Turbulence-resolving Spatio-temporal measurements of ABL flow with a large fleet of multicopter UAS., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16193, https://doi.org/10.5194/egusphere-egu24-16193, 2024.

Classical theories of atmospheric turbulence work well for isotropic turbulence. However, near the surface, as well as under strongly stable stratification, turbulence can be very anisotropic, due to the physical constraints of the ground and the buoyancy, respectively. This anisotropy has an impact on the mixing properties of turbulence, which need to be taken into account in parameterizations.

In atmospheric boundary-layer studies, turbulence anisotropy mainly refers to the difference in intensity of velocity fluctuations along different directions. This analysis can be performed along the principal directions of the Reynolds stress tensor. By doing so, a classification of turbulence according to its anisotropy, independent of the choice of the coordinate system where turbulence is measured, can be developed. This classification is an useful tool for improving current scaling relations of near-surface turbulence.

The present contribution focuses on the physical understanding of these different anisotropic states of turbulence, by exploring the possible sources which are driving  them. In addition, their relation with the variances and turbulent fluxes evaluated in the coordinate system commonly adopted in studies of near-surface turbulence is investigated. Special attention is given to results for stably stratified boundary layer, as under this condition the anisotropization of turbulence is considered one of the causes for poor performance of current parameterization at high Richardson number. 

How to cite: Gucci, F., Giovannini, L., Mosso, S., Stiperski, I., Zardi, D., and Vercauteren, N.: Physical understanding of anisotropy in the Reynolds stress tensor of near-surface turbulence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20206, https://doi.org/10.5194/egusphere-egu24-20206, 2024.

Almost all Earth System Models (ESM) use Monin-Obukhov similarity theory (MOST) to parameterize near surface turbulence. Despite its popularity, MOST has limited applicability and creates high uncertainties in very stable and unstable regimes, over heterogeneous and complex terrain, and is known to incorrectly represent the fluxes at the surface. Including turbulence anisotropy as a non-dimensional scaling parameter has recently proved successful in extending MOST to complex terrain for the scaling of variances and other near surface statistical properties.

Here we extend this approach to the scaling of surface gradients of mean wind and temperature, using data from five datasets ranging from flat and homogeneous to slightly complex terrain. The flux-gradient scaling relations exhibit large scatter, especially in unstable conditions where the data’s behavior is unclear. We show that adding turbulence anisotropy into the scaling of gradients allows to drastically reduce the scatter in the relations and develop new and more accurate parametrizations. This is especially true for the flux-gradient relations for wind shear (φ_m) in unstable conditions, and for temperature gradient (φ_h) both in unstable and stable regime.

The strong dependence of scaled wind speed gradient (φ_m), on turbulence anisotropy also allows us to finally settle the debate on the free convective regime, which clearly exhibits a -1/3 power law when anisotropy is considered. Whereas the strong dependence of scaled temperature gradients (φ_h) might explain a poorer performance of that scaling relation in predicting the surface sensible heat flux. Furthermore, the eddy diffusivities for momentum and heat and the turbulent Prandtl number are heavily modulated by anisotropy and the latter vanishes in free convective conditions.

These results further accentuate the need to incorporate turbulence anisotropy in boundary layer studies and parametrizations, paving the way for reliable surface parametrizations in ESMs.

How to cite: Mosso, S., Calaf, M., and Stiperski, I.: Flux-gradient relations: insights from anisotropy analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16046, https://doi.org/10.5194/egusphere-egu24-16046, 2024.

Anisotropy fundamentally defines the nature of turbulent flows in natural environments, engineering, and technology.  At large scales, turbulence rarely attains an energy state that is equipartitioned between the three velocity components or a state where turbulent stresses disappear. This deviation from isotropy underscores turbulence's essential role in promoting momentum transfer.

In canonical boundary layers, turbulence anisotropy emerges primarily from two distinct mechanisms: streamwise energy injections through shear forces and the vertical modulation of turbulent kinetic energy by buoyancy, acting either as a source (unstable stratification) or sink (stable stratification) of turbulence kinetic energy. Close to a solid surface turbulence additionally experiences wall blocking, limiting the energy in the wall-normal direction. Furthermore, in complex terrain, a multitude of factors intricately modify the turbulence anisotropy, thus altering the applicability of traditional similarity scaling.

Here, we use simplified Reynolds stress budgets to examine how stratification influences the normal stress components across a comprehensive range of measurement datasets from canonical to highly complex terrain. This reduced set of budget equations assume a balance between shear and buoyancy production and dissipation, and model the return to isotropy using a linear Rotta scheme adjusted by the isotropization of the production. This model provides expressions for normalized velocity variances as function of Richardson number, highlighting the change of anisotropy as stratification becomes progressively more dominant. In canonical terrain, the model is shown to capture the dependence of energy anisotropy on Richardson number away from the surface (heights above 60m), however, it fails in predicting energy anisotropy close to the surface. Furthermore, the increase of terrain complexity leads to a decoupling of the dependence of anisotropy and Richardson number not predicted by the model, and shows a consistent decrease of the contribution of streamwise  velocity variance and increase of spanwise velocity variance to the total TKE budget. Finally, a progressively more important wind turning with height with terrain complexity in neutral stratification causes near-surface turbulence to be more anisotropic over complex than over canonical terrain. 

Our findings outline the nuanced role of terrain in shaping turbulence anisotropy, providing avenues for enhanced turbulence modeling and highlighting limitations of conventional approaches in complex environments.

How to cite: Stiperski, I., Katul, G., and Calaf, M.: Examining Turbulent Flow Anisotropy: Insights from Simplified Variance Budget Analyses, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15135, https://doi.org/10.5194/egusphere-egu24-15135, 2024.

The planetary boundary layer (PBL) over the Tibetan Plateau (TP) imposes significant impact on regional and global climate, while its vertical structures and evolution features remain poorly understood. This study examines the evolution and possible mechanisms of daytime PBL turbulence profiles for cloud- and clear-sky conditions by using one-year observations from the radar wind profiler (RWP) network deployed over the TP, in combination with the measurements from the automatic weather station (AWS), millimeter-wave cloud radar (MMCR). The results show that the turbulence dissipation rate (e) are stronger and PBL height is higher in the norther part of TP (NTP), compared with those in the southern part of TP (STP). The presence of clouds inhibits turbulence transport within the PBL over the NTP, while the opposite effect was found over STP. Analysis of surface-air temperature difference  and wind shear data shows that both the thermal and dynamical effects strengthen the turbulence within PBL, and the thermodynamic effect is more important over STP than the NTP. The probability of PBL-cloud coupling is higher over the STP, and the cloud is found to enhance the PBL turbulence due to the strong wind shear, even although clouds can reduce the PBL height through radiative cooling effect. The findings help fill our knowledge gap in the PBL turbulence profiles throughout the whole TP, and highlight the significant role of the interaction between PBL turbulence and cloud in affecting the development of PBL turbulence over the whole TP.

How to cite: Guo, J., Meng, D., Guo, X., Sun, Y., Chen, T., and Xu, H.: Elucidating the boundary-layer turbulence profiles observed by a radar wind profiler network in the Tibetan Plateau , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1783, https://doi.org/10.5194/egusphere-egu24-1783, 2024.

Ultrafine particles (UFPs) are ubiquitously distributed throughout the global atmosphere. Their dimensions, often less than 100 nm, vary significantly from the surface. New particle formation (NPF) is a key process occurring in the planetary boundary layer (PBL). Newly formed particles are an important source of aerosols and cloud condensation nuclei (CCN) that influence clouds and climate, while the distribution of these new particles at different altitudes has rarely been studied. In-situ measurements of ultrafine particles (UFP) and New particle formation (NPF) observed at the ground and at the top of the Canton Tower (454 m) and Shenzhen tower located in southern China,both were analyzed using the measurements of multiple meteorological and physicochemical quantities, as both observed during a field campaign and simulated with the WRF-chem model. We found that turbulence and NPF characters vary considerably with heights, with UFP concentration diminishing by half from the surface to the tower top. This indicates the UFP transports upward from the ground in the lower boundary layer. A consistent relationship is established between the occurrences of NPF and the evolution of turbulence. The correlation between the exchange ratio at the tower top has correlated well with nucleation growth, suggesting that turbulence can play an important role in the episodes of NPF growth, whose growth rate is closely related to the turbulence exchange ratio, effectively dictating the ultrafine particle concentration before and during the lockdown period. A new mechanism is thus hypothesized: NPF happens eailer near the surface and grows faster at the upper PBL, attributed to condensable vapors being transported by turbulent vertical mixing in the boundary layer. Model simulations using the WRF-Chem model reveal that the exchange ratio changed the NPF parameters, supporting the proposed mechanism that the evolution of the PBL variation has a significant impact on NPF, which should not be omitted in the NPF research, since this physical factor could be a dominant one in the NPF mechanism.

How to cite: Wu, H.: Vertical transport of ultrafine particles and turbulence evolution impact on new particle formation based on tower observation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2582, https://doi.org/10.5194/egusphere-egu24-2582, 2024.

How are rainforest photosynthesis and turbulent fluxes influenced by clouds? To what extent are clouds affected by local processes driven by rainforest energy, water and carbon fluxes? These interrelated questions were the main drivers of the intensive field experiment CloudRoots-Amazon22 which took place at the ATTO/Campina supersites in the Amazon rainforest during the dry season, in August 2022. CloudRoots-Amazon22 collected observational data to derive causal-effect relationships between processes occurring at the leaf-level up to canopy scales in relation to the diurnal evolution of the clear-to-cloudy transition. First, we studied the impact of cloud and canopy radiation perturbations on the sub-diurnal variability of stomatal aperture. We found an asymmetry modulated by clouds that favors photosynthesis in the morning. Second, we combined 1 Hz-frequency measurements of the stable isotopologues of carbon dioxide and water vapor with measurements of turbulence to determine carbon dioxide and water vapor sources and sinks within the canopy. Using scintillometer observations, we inferred 1-minute sensible heat flux that responded within minutes to the cloud passages. Third, collocated profiles of state variables and greenhouse gases enabled us to determine the role of clouds in vertical transport. We then inferred the area fraction of cloud cover and cloud mass flux to probe the need of collecting a comprehensive data set to establish casualty between canopy and cloud processes and improve the representations in weather and climate models. Our findings contribute to advance our process knowledge of the coupling between cloudy boundary layers and primary carbon productivity of the Amazon rainforest.

How to cite: Vila-Guerau de Arellano, J. and the CloudRoots-Amazon22: CloudRoots-Amazon22: Integrating clouds with photosynthesis by crossing scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2905, https://doi.org/10.5194/egusphere-egu24-2905, 2024.

in the atmosphere over mountains – programme and experiment (http://www.teamx-programme.org/)  are also presented.

How to cite: Zardi, D.: Turbulence in thermally-driven slope winds, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15299, https://doi.org/10.5194/egusphere-egu24-15299, 2024.

The Chilean Altiplano is a region composed by endorheic basins immersed in a complex topography. These basins are predominantly characterized by desert surfaces in which small-scale heterogeneities can be found in the form of salt flats with shallow, salt water lagoons, that act as preferential pathways for evaporation (E). Thus, understanding the processes that control E in the lagoons is essential for water balance predictions, and to understand the impacts of climate change on the region.

In addition to the local saline lagoon and desert conditions, the atmospheric boundary layer (ABL) and its interaction with large-scale forcing, play a key role in regulating E. Observations over a salt water lagoon in the Salar del Huasco basin show that in the morning E is virtually zero, with turbulence as a limiting factor due to the absence of wind. Under these conditions, a shallow, stable ABL is formed over the water. In the afternoon, E is triggered by the entrance of a thermally driven and topographically enhanced regional flow characterized by strong winds. Simultaneously, the ABL turns into a deep mixed layer similar to the one observed over the surrounding desert.

In this research we investigate the coupling between the ABL and E drivers using a land atmosphere model, observations and a regional model. We also analyze the ABL interaction with the aerodynamic and radiative components of E using the Penman equation adapted to salt water. Our results demonstrate that the morning ABL is controlled by the local advection of warm air (∼5 Kh-1), resulting in a shallow (<350 m), stable ABL, with virtually no mixing and no E (<50 Wm−2). The warm air advection ultimately connects the ABL with the residual layer above, sharply increasing the ABL height by ∼1 km around midday. During the afternoon, the regional flow arrives to the lagoon, causing an increase in wind (∼12 ms-1) and an ABL collapse due to the entrance of cold air (∼-2 Kh-1) with a shallower ABL (∼-350 mh-1). The turbulence produced by the wind decreases the aerodynamic resistance and mixes the water body releasing the energy previously stored in the lagoon. The ABL feedback on E through the vapor pressure enables high E values (∼450 Wm-2). These results are exemplary to E of water bodies in semiarid conditions and emphasize the importance of understanding ABL processes when describing E drivers.

How to cite: Hartogensis, O., Aguirre Correa, F., Suárez, F., Lobos-Roco, F., Ronda, R., and Vilà-Guerau de Arellano, J.: Evaporation driven by Atmospheric Boundary Layer Processes over a Shallow Salt-Water Lagoon in the Altiplano, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17882, https://doi.org/10.5194/egusphere-egu24-17882, 2024.

The Land surface Interactions with the Atmosphere over the Iberian Semi-arid environment (LIAISE) field experiment took place in July 2021 in the Ebro River Valley in the northeast of Spain. In the domain of the LIAISE field campaign, thermal surface heterogeneity is induced by irrigation which was applied to agricultural fields that cover ∼65% of the LIAISE region contrasting with the remaining 35% of the region covered by non-irrigated agricultural fields. Observed Bowen ratios reach approximately 20 in non-irrigated fields, while observed Bowen ratios are approximately 0.1 in the irrigated fields. This contrast could lead to an interaction of scales that range from the a regional scale that encompasses both the irrigated and non-irrigated areas (∼10 km) down to a scale of an individual field (∼100 m).  In addition to surface fluxes, profiles of both the mean state of the atmospheric boundary layer (ABL) and turbulent transport in the ABL were measured over both the irrigated and non-irrigated landscapes. Observations confirm that the surface heterogeneity is felt most strongly near the surface; however, approximately 1000 m above ground level, there appears to be a blending height in which heterogeneity mixes so that the observed ABL potential temperature and specific humidity profiles are similar over both landscapes. Conversely, profiles of turbulent transport shows notable differences between the irrigated and non-irrigated boundary layers. Buoyancy flux over the irrigated area is driven by moisture fluxes, and above an internal boundary layer (approximately 25% of the non-irrigated ABL height), turbulent fluxes of scalers reach their maximum. Turbulence kinetic energy is higher over the non-irrigated landscape because of the increased buoyancy from the surface sensible heat flux, and the observed ABL heights are 100-500 m higher in the non-irrigated landscape than the irrigated landscape.

In this study, we discuss novel experiments that combine the synoptic- and meso-scale forcing (ERA) with the explicit simulation of secondary circulations driven by surface heterogeneity using large-eddy simulation (LES).   The surface of the LES is defined with prescribed sensible and latent heat fluxes from observations. With the LES, we aim to better understand the development of the ABL over the LIAISE domain and how the ABL differs in space between the irrigated and the non-irrigated areas Furthermore, we focus on the turbulent transport – both vertically and horizontally in space – to illustrate the most important processes which contribute to the locally observed ABL.

How to cite: Mangan, M. R., Vila-Guerau de Arellano, J., van Stratum, B., Lothon, M., Canut, G., and Hartogensis, O.: The Diurnal Evolution of Atmospheric Boundary Layers in the LIAISE Field Campaign , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16872, https://doi.org/10.5194/egusphere-egu24-16872, 2024.

*This work is part of the project "trainABL" funded by the European Commission throgh the European Research Council (ERC) under its Starting Grant Scheme (ERC-2019-StG Grant No. 851374)

How to cite: Ansorge, C.: Comparison of Wind profile models across the Ekman layer, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18003, https://doi.org/10.5194/egusphere-egu24-18003, 2024.

In numerical weather prediction models, the local first-order closure of turbulence, also known as K-theory, is widely used to parameterize the turbulent flux in the surface roughness layer. The non-local effects of large eddies in turbulent flows are not resolved by K-theory, leading to the flux imbalance that the simulated and measured fluxes are typically smaller than the true heat flux. Higher order closure schemes mitigate the flux imbalance problem but lead to increased complexity in parameterization and higher demands on computational resources. At the same time, flux imbalance models based on large eddy simulation results have been able to capture non-local effects of the energy-containing large eddies that span the entire boundary layer and improve the flux imbalances on both simulation results and eddy covariance measurements. These models inspired us to propose a new modified K-theory based on a correction factor that includes the non-local effects mentioned above, without using an extra term (e.g. counter-gradient flux). The formulation of the modified K-theory is straightforward and requires atmospheric stability parameters (u*/w*) and the ratio of measurement to boundary layer height (z/Zi), which are readily available in simulations and observations.

To test the performance of the modified K-theory, an idealized large eddy simulation was performed over a dry convective boundary layer with a prescribed sensible heat flux at the land surface. The result shows that the K-theory underestimates the sensible heat flux by 18% due to the mesoscale circulations, while the proposed modified K-theory reduces the underestimation to less than 6%, offering the potential to improve the parameterization in numerical weather prediction.

How to cite: Zhang, L., Poll, S., and Kollet, S.: A Nonlocal First-Order Closure PBL Parameterization for Sensible Heat Flux using Flux Imbalance Models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7952, https://doi.org/10.5194/egusphere-egu24-7952, 2024.

In the pursuit of advancing our comprehension of the atmospheric boundary layer and the associated exchange processes near the surface, the accessibility of high-quality data assumes a pivotal role. An open-access approach is acknowledged for catalyzing collaborative efforts, empowering researchers globally to harness available information for their investigations. This has the potential to refine existing models, validate hypotheses, and instigate innovations in climate modeling and predictive simulations. Here, we introduce an open benchmark data repository, accessible through static collection of DOIs, to share the statistics of simulations for turbulent Ekman flow. This data, forming the foundation for numerous publications on Ekman flow, has been established as a suitable virtual lab environment in prior works for studying crucial aspects of the atmospheric boundary layer. We believe that the availability of this data under the FAIR paradigm has the potential to facilitate further exploitation, enhancing our understanding of process-level intricacies in the atmospheric boundary layer.
The data is being generated since 2011 using the tLab tool-suite (github.com/turbulencia/tlab) for direct numerical simulation (DNS) on some of Europe’s largest supercomputers, including juqueen and juwels at Jülich Supercomputing Centre, and hawk at Höchstleistungsrechenzentrum Stuttgart. It is now accessible in the long-term data repository refubium.fu-berlin.de of Freie Universität Berlin.
The inaugural contribution to this repository is a comprehensive, curated set of data exploring the influence of turbulence scale separation, specifically the Reynolds number. A series of simulations spans a range of Reynolds numbers, corresponding to a variation of approximately tenfold in the friction Reynolds number Re_τ. The shared dataset encompasses various parameters, including vertical profiles of velocity, budget terms of scalar and momentum budgets, statistical moments up to the third order of velocities, scalars, and derivatives, providing a holistic view of Ekman flow dynamics across a range of Reynolds numbers. This enables the identification of inviscid scaling behavior and the development of scaling theories for the application of these simulations to real-world problems.
While the dataset also captures effects of stable stratification and rough surfaces, these aspects are, beyond the scope of this abstract.

Keywords— Numerical simulation, Ekman flow, Turbulence, Surface layer, Simulation Theory

∗ This work is funded by the ERC Starting Grant "Turbulence-Resolving Approaches of the Intermittently Turbulent Atmos-
pheric Boundary Layer [trainABL]" of the European Research Council (funding ID 851347). The data was generated under that
computing grants hhh07, hku24, stadit at Jülich supercomputing centre and trainABL / Bundesprojekt 44187 at Höchstleistungs-
rechenzentrum Stuttgart)

How to cite: Issa, S., Ansorge, C., Pedro Mellado, J., and Kostelecky, J.: Open access Data Sets of Vertical Profiles for Turbulent Ekman Flow generated by DNS tlab code, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9484, https://doi.org/10.5194/egusphere-egu24-9484, 2024.

The complexity and variety of phenomena that can occur in coastal areas (e.g. breezes, internal boundary layers, low-level jets (LLJ)) often result in wind profiles strongly deviating from the Monin-Obukhov similarity theory. Moreover, the lack of offshore experimental data leads to gaps in knowledge of the marine coastal atmospheric boundary layer (MCABL). Characterizing the wind resources in MCABL has been identified by Veers et al. (2022) as one “Grand Challenge” for the development of offshore wind farms.

To partially fill these gaps, a joint numerical and experimental study is currently being performed. In 2020, scanning LiDAR measurements were carried out within a few kilometers of the French Atlantic coastline (Conan and Visich, 2023). In parallel, mesoscale to microscale simulations are performed with the Weather Research and Forecasting (WRF) code, using the grid-nesting method to progressively decrease the horizontal mesh size from a few kilometers (RANS modeling) down to a hundred meters (LES modeling). The simulation, giving access to more atmospheric variables in a large area, allows a complementary analysis.

On a particular week of this experiment, complex velocity profiles have been observed in the LiDAR data, highlighting the presence of LLJ and high wind-shear events. Velocity profiles from RANS simulations show good comparison with LiDAR data, which suggests that the mechanisms responsible for the observed phenomena are well reproduced. In addition, these large-scale simulations allow the identification of a complete sea-breeze circulation in the complex coastal area of Brittany.

The marine extent of the sea-breeze can be defined as the isoline where cross-coast velocity component decreases with the distance from the coast to a value of 1 m/s (Arritt, 1989 ; Finkele et al., 1995). The RANS results indicate that the sea-breeze can reach a distance of 70 km offshore during the studied period. A first analysis of the simulations also suggests that the nighttime LLJ observed on the Atlantic coast is related to the residual of a sea-breeze front moving southward from the north coast of Britanny.

Analysis of the LES simulations will permit to study more precisely the onset of the sea-breeze, the evolution of the LLJ across the coastline (related to transition in atmospheric stability and surface roughness) or the turbulence kinetic energy budget in the jet core.

Arritt, R.W. 1989. Quarterly Journal of the Royal Meteorological Society 115 (487): 547‑70. https://doi.org/10.1002/qj.49711548707.

Conan, B.,and A. Visich. 2023. Wind Energy Science Discussions, October, 1‑23. https://doi.org/10.5194/wes-2023-141.

Finkele, K., et al.. 1995. Boundary-Layer Meteorology 73 (3): 299‑317. https://doi.org/10.1007/BF00711261.

Veers, P., et al.. Wind Energy Science 7 (6): 2491‑96. https://doi.org/10.5194/wes-7-2491-2022.

How to cite: Landreau, M., Conan, B., and Calmet, I.: Analysis of coastal breeze and low-level jets events from numerical modeling and LiDAR measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10013, https://doi.org/10.5194/egusphere-egu24-10013, 2024.

The planetary boundary layer height (PBLH) is a crucial component in almost all planetary boundary layer (PBL) parameterizations, and the PBLH is calculated using a method based on the bulk Richardson number (Ri_B), which utilizes a threshold value of Ri_B called the critical bulk Richardson number (Ri_cr). In most of the PBL schemes, Ri_cr prescribed as one single value, and its dependency on thermal stratification has been ignored. In the present study, an effort has been made to incorporate Ri_cr based on different stratification conditions following a study by Zhang et al. (2014) in the PBL parameterization proposed by Holtslag and Boville (1993) of the National Centre for Atmospheric Research Community Atmosphere Mode version 5 (NCAR-CAM5). The modified scheme is evaluated over Indian land and associated different climatic zones in simulating PBLH, surface turbulent fluxes, near-surface atmospheric variables, and precipitation during the winter (DJF), pre-monsoon (MAM), monsoon (JJA), and post-monsoon (SON) seasons. The simulations with the default and modified schemes have been carried out at a spatial resolution of ~1^o for a period of six years, discarding the first year as spin-up time and considering the last five-year simulation for the analysis. The study reveals that the modified scheme is able to produce more accurate estimates for PBLH than the default scheme compared to the ERA5 reanalysis dataset over Indian land, which further enhances the accuracy of turbulent transport of heat, moisture, and momentum inside the PBL under various atmospheric stability regimes. The modified scheme noticeably improved the simulation of surface sensible and latent heat fluxes, surface air temperature, and precipitation compared to the default scheme over Indian land during all four seasons.

How to cite: Namdev, P., Sharan, M., and Mishra, S. K.: Impacts of using thermal stratification dependent critical bulk Richardson number in a PBL scheme of a climate model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11351, https://doi.org/10.5194/egusphere-egu24-11351, 2024.