Surface-layer stability is important in many processes, such as the surface energy budget, atmospheric pollution, and boundary-layer parametrization. Most previous studies on stability, however, conducted either theoretical or observational investigations at specific sites, thus leaving a gap with regard to the large-scale pattern. Here, wind speed and temperature observations at multiple heights from the wind-tower network of China are used to estimate the stability during the 2009–2016 period. A series of data-quality-control procedures are conducted and data from 170 wind towers with more than 2 years’ worth of valid observations are selected. The degree of stability is classified by the Obukhov length, which is derived from the wind speed and temperature at 10 m and 70 m above ground level, combined with information regarding the roughness length. Overall, the occurrence frequency of surface-layer instability exhibits significant temporal and spatial variability, being particularly larger in spring and summer than in autumn and winter. The maximum frequency of summertime instability occurs in the time period 1000–1200 local solar time, approximately 2 h earlier than in autumn. Geographically, the peak instability frequency occurs much earlier in the day in north-west China than in other regions, likely owing to the arid and semi-arid land cover. Also noteworthy is the steady increase in instability frequency observed during the period analyzed here, likely resulting from the reduction in the vertical gradient of wind speed. Our findings call for explicit consideration of stability variability in the wind-energy industry and in fundamental boundary-layer investigations in China.

How to cite: Li, J.: Assessing the Surface-Layer Stability over China Using Long-Term Wind-TowerNetwork Observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6812, https://doi.org/10.5194/egusphere-egu23-6812, 2023.

Despite the importance of low-level jets (LLJ), their driving mechanisms are not well understood largely due to a shortage of suitable observational data. The classical description for LLJ follows the concept of inertial oscillations at night (NLLJ). Their development is associated with the nocturnal decoupling of winds from the surface friction due to the formation of a near-surface temperature inversion. However, LLJs have also been connected to convectively generated Cold Pools (CP) in kilometre-scale model. CPs are mesoscale areas of cool and dense air formed through convective downdrafts underneath precipitating clouds. Data from the Field Experiment on Submesoscale Spatio-Temporal Variability (FESSTVal) gave us the unique opportunity to test the hypothesis that LLJ formation is also connected to CP passages. We used measurements from three Doppler LIDAR instruments located about 6 km apart from each other, a microwave radiometer and radiosondes for atmospheric profiling, and a large and dense network of surface measurements for the CP detection. During the three-month long field experiment, about 4.7% of all identified LLJ profiles were connected to a CP event (CPLLJ). The average length of CPLLJs was almost two hours. The core of CPLLJ had a mean wind speed of 7 ms⁻¹ and a mean height of 207 m. Using Doppler LIDAR also allowed us to look at wind gusts in the core of the CPLLJs. We measured wind gust of up to 17.5 ms⁻¹ in their core, which exceeds the maximum gust of 15 ms⁻¹ in NLLJs. Close to the surface, the wind speed differences between CPLLJs and NLLJs were even larger than in the core. Most measured CPLLJs appeared at the time of the passage of the CP front and lasted not long after the front has passed, with an interesting exception of a six-hour long CPLLJ during daytime on 29 June 2022. In wind and temperature profiles, we clearly see density currents reaching the experiment site paired with the appearance of strong LLJ profiles. After the passage of the CP front, relatively weaker LLJ profiles were seen. The measurements show that the CP favoured the development of a stably stratified near-surface layer. In a first moment, when the CP front reached the site, there was a mean cooling between the surface up to at least 400 m a.g.l.. After that, the layers bellow 200 m a.g.l. continued to cool, forming a temperature inversion, similar to what one would expect from nocturnal radiative cooling. Radiosondes indicate the typical daytime unstable conditions at the surface and a neutral stratification in the well-mixed boundary layer before the CP arrived. At the time of the CP passage, unstable stratification was seen over a deeper layer followed by the development of a stable stratification in the two hours after the front passed. These conditions led to the formation of a strong and long-lived CPLLJ during daytime. The observations from the FESSTVaL campaign gave first robust evidence that CPs can favour reduced frictional coupling of the wind field to the surface as a prerequisite for generating LLJs.

How to cite: Weide Luiz, E. and Fiedler, S.: Do cold pools generated by convective downdrafts allow the development of low-level jets?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11526, https://doi.org/10.5194/egusphere-egu23-11526, 2023.

A series of discrepancies between field observations and the traditional thermal energy balance derived from the 1st law of thermodynamics are investigated. Intrigued by some historically known puzzles such as surface energy imbalance, failed potential temperature conservation, and dissimilarity between temperature and humidity, the investigation focuses on physical processes in the atmospheric boundary layer that are uniquely controlled by the diurnal variation of surface heating/cooling. Examination of temperature changes is extended to air-temperature-related variables such as turbulent heat fluxes and temperature variances. Inconsistency between field observations and the traditional thermal energy balance is found not only in their magnitudes but also in their diurnal cycles. Inability of the traditional thermal energy equation for explaining all the observations that are distinctively related to air temperature changes challenges validity of the traditional thermal energy balance theory. 

The research is supported by NSF AGS-2203248.

How to cite: Sun, J.: Discrepancies between Boundary-layer Observations and the Traditional Thermal Energy Balance, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1681, https://doi.org/10.5194/egusphere-egu23-1681, 2023.

Filomena snowstorm impacted a large part of the Iberian Peninsula during January 2021, especially affecting the central part of Spain, and covering the Madrid region with up to 50 cm of snow.

In this work, we analyse data from a micrometeorological station (GuMNet-Herrería) placed in a rural environment in the northwest of the Community of Madrid. The objective is to determine the influence of the microscale on the extremely low temperatures reached after Filomena's passage, as well as to better understand the physical processes associated with these extreme conditions.

Although the snowfall lasted only for 2 days, the snow was present on the surface for more than 10 days, already with stable synoptic conditions, accompanied by a weak turbulent transfer between the surface and the lower part of the atmospheric boundary layer. These days after, extremely low temperatures were recorded, reaching minima of up to -26.5 ºC in the central part of the Iberian Peninsula. The presence of snow on the surface modified significantly the components of the surface energy balance (SEB). This included a reduction in the available net radiation at the surface as result of increased albedo and emissivity of the surface, compared to standard conditions (previous period to Filomena), as well as in the turbulent fluxes, contributing to some records of minimum temperatures. The persistence of the snow cover also affected the soil temperatures, keeping the ground heat flux practically constant.

How to cite: Fernández-Castillo, P., Román-Cascón, C., and Yagüe, C.: Influence of the extraordinary Filomena snowstorm on the surface energy balance and its relationship with the subsequent very-low surface temperatures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5664, https://doi.org/10.5194/egusphere-egu23-5664, 2023.

Air pollution is one of the main hazards for human health worldwide, especially in cities. Surface emissions are the main responsible for the presence of pollutants in the near atmosphere, but meteorological conditions typically play a fundamental role in their accumulation or dispersion. In this work, we focus on the near-surface atmospheric stability and turbulence, for which data from four field campaigns with meteorological and pollutant measurements belonging to the AIRTEC-CM project^(*) have been analysed. Available data correspond to the winter and summer seasons of 2020 and 2021 at two public sites located in the city centre of Madrid: a University (ETSII) and a Hospital (HCSC). The evolution of turbulence and stability and their relationships with pollutants such as NO₂, PM_2,5 and PM₁₀ are investigated. To study turbulence, an analysis of friction velocity and turbulent kinetic velocity is carried out, while the stability parameter (Obukhov length) and the Richardson number obtained by means of the simplified universal similarity functions have been considered for the analysis of the stability. Through the analysis of the mean daily cycle of pollutants, it has been observed how its evolution shows two maxima centered on the morning and evening transitions. The results obtained indicate that pollutant concentrations are strongly influenced by the daily cycle of stability and turbulence, marked by the presence of a maximum of turbulence in the central hours of the day (when the sensible heat flux is greater) and a strong decay of this in the day-night transitions, which in the case of the afternoon transition coincides with the shift from the convective to the stable boundary layer. In addition, the time when this turbulence decay occurs modulates the pollutant concentration values reached, added to the intensity of the stability itself.

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

How to cite: Ortiz-Corral, P., Román-Cascón, C., Serrano, E., Sastre, M., Maqueda, G., and Yagüe, C.: Effects of near-surface atmospheric stability and turbulence on air pollution levels in Madrid, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12568, https://doi.org/10.5194/egusphere-egu23-12568, 2023.

Winds in coastal areas are particularly complex due to the drastic change of roughness and thermal properties between the sea and the land areas. Besides, the coastal topography, the shoreline irregularities, the surface state (land cover/use, soil moisture, sea surface temperature (SST), wind waves), and the interactions with the upper parts of the atmospheric boundary layer (ABL) add more complexity to the final characteristics of the surface winds of these regions.

Among coastal winds, coastal breezes are especially common thermally driven flows formed in mid-latitude regions under fair-weather synoptic conditions. Under these situations, the thermal gradient between the sea and the ocean becomes more important, generating pressure gradient forces that lead to onshore winds during the daytime and offshore during the night. The impacts of these winds are broad and varied: they transport humidity, pollutants, and other physical properties in these regions; they can initiate convection (and even trigger the formation of storms), and they also drive the surface coastal currents, among others. From a societal point of view, the coastal breezes are crucial for the wind power industry, air-quality forecasts, maritime sports, and simply for the refreshing impact they cause, an aspect especially important in some areas commonly affected by extreme maximum temperatures and heat waves. Therefore, a correct understanding of the physical characteristics of the coastal breezes is a needed step to correctly forecast them and to be able to investigate their future trends.

In this work, we present an observational analysis of the coastal breezes observed in the Gulf of Cádiz. We highlight some differences found between the breezes formed at the sea and at the land areas from observational measurements. Besides, we use the mesoscale Weather Research and Forecasting (WRF) model to simulate key case studies, showing how the interaction with the background synoptic wind is very important for the final characteristics that the breezes have. Related to this, we have observed how the effect of the changes in the surface (SST, soil moisture) on the breeze’s characteristics depend on the wind vertical profile (background wind). That is, surface changes impact the ABL mixing and the momentum transfer from higher levels, which seems to be the main mechanism that impact the breezes at lower levels, even more than the surface thermal gradient effect.

How to cite: Román-Cascón, C., Brnas, T., Ortiz-Corral, P., Steeneveld, G.-J., Vázquez, Á., Bruno, M., Izquierdo, A., Reyes, J., Romero, J., Adame, J. A., Sun, J., and Yagüe, C.: Coastal winds in the Gulf of Cádiz (southwestern Iberian Peninsula): insights from observations and models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12826, https://doi.org/10.5194/egusphere-egu23-12826, 2023.

Ecosystems plays a key role on the interaction between the land surface and the atmospheric processes being responsible for strong feedback processes that affect the climate by modifying the relative contribution of the latent and sensible heat to the total energy of the atmospheric air, i.e., the energy partitioning processes. The mechanisms and consequences of this feedback are uncertain and must be studied to evaluate their influence on global climate change.

In this study, our overall objective was to assess the Gross Primary Production (GPP) dynamics and the energy partitioning patterns in three different European forest ecosystems through time series analysis of eddy covariance data. The three contrasted forest types in terms of functioning and climate were an Evergreen Needleleaf Forest in Finland (ENF_FI), a Deciduous Broadleaf Forest in Denmark (DBF_DK), and a Mediterranean Savanna Forest in Spain (SAV_SP). In each site there was and eddy covariance flux tower from which meteorological data, carbon and energy fluxes were analyzed. Firstly, a univariable time series analysis of all variables was made by means of the Buys-Ballot tables, i.e., average year, to study the intra-annual dynamics and then, through the use of the autocorrelation function the interannual dynamics were assessed.  Finally, causality of GPP and energy fluxes was studied with Granger causality tests.

Results show that temperature and solar radiation were the main limiting factors in the Northern ecosystems while water availability was determinant for growth in the Mediterranean ecosystem. The autocorrelation function showed that GPP and the meteorological variables in the SAV_SP were more irregular and show lower memory at the long term than at the short one. In addition, this ecosystem presented higher radiation and a larger amount of H+LE, showing the highest Bowen ratio and a lower primary production efficiency in terms of total energy (GPP/(H+LE)). On the contrary, both northern ecosystems showed similar production efficiencies in terms of total energy. However, the DBF_DK showed lower Bowen ratio related to a larger amount of latent heat in relation to sensible heat in associated to the larger plant activity in this forest. Finally, the Granger causality tests showed that the vegetation feedback to the atmosphere was more noticeable in the ENF_FI and the DBF_DK at the short term, influencing latent and sensible heat fluxes.

In conclusion, the impact of the vegetation on the atmosphere influences the energy partitioning in a different way depending on the vegetation type, which makes essential the study of the vegetation dynamics at the local scale to parameterize with more detail these processes and build improved global models.

How to cite: Cicuéndez, V., Litago, J., Sánchez-Girón, V., Román-Cascón, C., Recuero, L., Saénz, C., Yagüe, C., and Palacios-Orueta, A.: Influence of gross primary production in energy partitioning in three different forest ecosystems based on Eddy Covariance time series analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6371, https://doi.org/10.5194/egusphere-egu23-6371, 2023.

The entrainment zone (EZ) capping the convective boundary layer (CBL) is documented using lidar turbulent-scale observations. Sensible and latent heat fluxes have been measured during one hundred hours in CBL temperate and arid regions in free-cloud meteorological conditions. The EZ fluxes have been confronted with scalar gradients, integral scales of turbulence, wind shear, and surface sensible heat flux.  In agreement with former observations in stratified surface layer or with EZ large eddy-simulation (LES) studies, Lidar observations show that the buoyant oscillation period associated to the vertical velocity variance are found to be universal relevant parameters for EZ scalar fluxes and gradients. Attempts to introduce non-local CBL scales like the turbulent vertical velocity scale and height, the scalar interfacial layer jumps and the surface sensible heat flux globally increases the scatter of the data. Non-local parametrization particularly failed for EZ latent heat flux compared to sensible heat flux and for weak surface heat flux as it is usually the case in temperate region. Investigating a possible non-local parametrization of EZ vertical velocity variance, it was found that EZ wind shear and then EZ gradient Richardson number play a negligible role. Rather, observations often showed an excess of EZ vertical velocity variance with respect to CBL similarity law that may be explained by a significant contribution of wave-turbulence interaction in the entrainment layer.

How to cite: Gibert, F., Edouart, D., Monnier, P., Collignan, J., Lopez, J., and Cénac, C.: Scalar turbulent flux observations in the entrainment layer and assessment of current parametrizations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5566, https://doi.org/10.5194/egusphere-egu23-5566, 2023.

The main exchange of energy and mass between the atmosphere and the surface occurs through the means of turbulent processes in the boundary layer of the atmosphere. A modern atmospheric dynamics models use simplified schemes for calculating energy exchange with the surface, based on the Monin-Obukhov similarity theory (MOST). The main requirement of MOST is the uniformity of the underlying surface. This simplification reduces the accuracy of the forecast, especially in regions with complex (heterogeneous) orography, such as in urban conditions. The obtained regularities in the future may allow us to choose the most accurate parameterization for better use of MOST in conditions of a geometrically complex surface and increasing the accuracy of the forecast for urbanized territories.

This paper presents the result of the analysis of the data series for period from 2020 to 2022 obtained from the eddy covariance tower installed in the Meteorological observatory of Moscow State University. Acoustic anemometers with a frequency of 20 Hz record three components of wind speed  and acoustic temperature at altitudes of 2.2 m, 11.1 m and 18.8 m. For processing high-frequency mast data and calculating the static characteristics of turbulence, a set of programs implemented by the authors is used. Gaps are filled by a new algorithm proposed in [3].

Based on a long series of measurements, the seasonal and daily variability of heat and momentum fluxes over an urbanized surface was analyzed. The detailed statistical analysis of the influence of eddy structures was carried out on the formation of turbulent fluxes in the city. The method proposed in [2] was used to identify coherent vortices. The method is based on the hypothesis of the relationship of third and second moments, described by the ratio:

where C∼1 is non-dimensional constant, and S_w is skewness of vertical velocity [1]. The compliance of third moments with theoretical values was established for various stratification conditions in 80% of cases. The result indicates a significant contribution of coherent structures to the formation of vertical fluxes over a geometrically complex surface, which is consistent with the estimates received earlier [2, 4].

References

• [1] Abdella K. et al. A new second-order turbulence closure scheme for the planetary boundary layer //Journal of the atmospheric sciences. – 1997. – Т. 54. – №. 14. – С. 1850-1867.
• [2] Barskov K.V. et al. Two regimes of turbulent fluxes above a frozen small lake surrounded by forest //Boundary-Layer Meteorology. – 2019. – Т. 173. – №. 3. – С. 311-320.
• [3] Drozd I.D. et al. Comparative characteristics of gap filling methods in high-frequency data of micrometeorological measurements //IOP Conference Series: Earth and Environmental Science. – IOP Publishing, 2022. – Т. 1023. – №. 1. – С. 012009.
• [4] Pashkin A.D. et al. An experimental study of atmospheric turbulence characteristics in an urban canyon //IOP Conference Series: Earth and Environmental Science. – IOP Publishing, 2019. – Т. 386. – №. 1. – С. 012035.

How to cite: Drozd, I., Gavrikov, A., Stepanenko, V., Repina, I., Artamonov, A., and Pashkin, A.: Atmospheric turbulence structure above urban heterogeneous surface, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16390, https://doi.org/10.5194/egusphere-egu23-16390, 2023.

The Sichuan Basin (SCB) with complex mountain-basin topography, located immediately to the east of the Tibetan Plateau (TP) in southwest China, is identified as a region with severe PM_2.5 pollution over China. To comprehensively understand the SCB terrain effect on the atmospheric environment change, we investigated the effect degree and meteorological mechanism of mountain-valley winds on wintertime PM_2.5 in the western SCB, thermally driven mountain-valley winds between the mountains of eastern TP and the western edge of SCB based on near-surface observations of PM_2.5 and the ERA5 reanalysis data of meteorology. The results show that the western SCB exhibits a significant diurnal change of mountain-valley winds, shifting between daytime easterly flows and nighttime westerly flows over the western edge of SCB. The frequency of the mountain-valley winds was accounted for 39% of the study’s duration, with the valley and mountain wind-controlling periods being from 2:00 pm to 5:00 pm and 01:00 am to 05:00 am in local time, respectively, and the remaining time being the transition period. Notably, a reduction of 4.5~20.7μg m^-3 in near-surface PM_2.5 concentrations averaged over the western edge of SCB, decreasing 6~74% in the PM_2.5 pollution during the days of mountain-valley winds, which indicates that the mountain-valley winds could alleviate wintertime near-surface PM_2.5 in improving air quality over the western SCB. The easterly wind speed was uplifted by 18% during the valley wind-controlling period, corresponding to a 22% reduction in the near-surface PM_2.5 levels driven by the mountain-valley winds. The westerly wind speed increased by 50% at the mountain wind-controlling period with a 20% reduction in PM_2.5, reflecting the attenuating effect of the favorable atmospheric diffusion conditions on PM_2.5 pollution over the western SCB. The daytime noticeably enhanced easterly wind and the strong updraft flows over the eastern slope of TP promoted the dilution and diffusion of air pollutants over the western edge of SCB, and the nocturnal downhill flows along the slope in the westerly winds on the western edge of SCB brought clean TP air to the polluted SCB region in southwest China.

How to cite: Zhang, Y., Zhao, T., Shu, Z., Zhu, Y., Fu, W., and Liang, D.: Attenuation of mountain-valley winds on wintertime PM2.5 change over the western Sichuan Basin, Southwest China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7929, https://doi.org/10.5194/egusphere-egu23-7929, 2023.

Tomographic 3D reconstructions of artificial puff releases of SO₂ were obtained from 2D images taken with UV cameras.  These novel 3D reconstructions provide information on the distribution of concentration from a unique experimaental campaign dataset collected in Rena, Norway. The numerical solutions of the inverse problem of obtaining 3D reconstruction form 2D images were addressed with algebraic methods. Preliminary turbulence analysis of the puff concentration pdf, spatial moments, and 2-point statistics are presented. The experimentally obtained concentration pdf of a puff can be compared with different statistical models found in the literature. The time series of the puff spatial moments are obtained from the 3D concentration field directly in relative coordinates from observations. The distance-neighbour function can also be estimated directly from the 3d puff concentrations. The time series of 3D reconstructions of puffs entail promising posibilities for improving physical parametrizations in numerical dispersion models.

How to cite: Pisso, I., Cassiani, M., Kylling, A., Stebel, K., Schmidbauer, N., Stohl, A., Dinger, A. S., Ardeshiri, H., and Park, S.-Y.: Turbulent dispersion of artificial SO2 puffs in the PBL from tomographic reconstructions of the concentration, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16243, https://doi.org/10.5194/egusphere-egu23-16243, 2023.

Inside the Marine Atmospheric Boundary Layer (MABL) turbulence drives a large amount of physical processes through a dynamical coupling. Understanding this coupling is a key issue in weather and climate modeling, but an adapted statistical representation is still lacking. A strong limitation comes from the non-Gaussianities existing inside the MABL. We seek an approach to describe statistically the couplings across scales, which is poorly measured by the power spectrum. Recent developments in data science provide new tools as the Wavelet Scattering Transform (WST), which gives a low-variance statistical description of non-Gaussian processes and offers to go beyond the power spectrum representation.

We proposes to apply WST technique on turbulent moments recorded during the EUREC4A campaign in trade-wind cloud regimes. Using WST analysis on both fluctuating time series and realistic Large-Eddy Simulations (LES), we study how the different scales in turbulent flows interact between each other in the MABL. Are the turbulent flows organised or purely random in the MABL ? Do the couplings change for different cloud organisations ? Do the models show evidence of such scale couplings ?

In this presentation, we first look at the expected WST coefficients law for turbulent flows in the inertial subrange. Second, we present what are the WST coefficients for the measured turbulent moments and how they evolve for different cloud organizations.

How to cite: Gauvrit, E., Bouin, M.-N., Delouis, J.-M., and Boulanger, F.: Unveiling the turbulence scale couplings in fluctuating time series during EUREC4A, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13685, https://doi.org/10.5194/egusphere-egu23-13685, 2023.

Idealised models of convection such as Rayleigh-Bénard convection, horizontal convection etc. have been widely used to study the behaviour of natural fluid systems including but not limited to the atmosphere, the oceans and the flow of lava in the earth's core in a simplified setting ^1,2. While such idealised models include only a small subset of the physical processes occurring in nature, their simplified dynamics allows for easier interpretation and study of the interactions of individual physical processes. 

In this numerical study, we consider the case of an idealised moist convecting thermal system, with various Dirichlet and Neumann boundary conditions for the temperature and water vapour mixing ratio. The model includes a vertical temperature lapse-rate, the release of latent heat due to the condensation of water vapour and a constant bulk-cooling term to simulate moist convection accompanied by radiative cooling in the earth's atmosphere. This study follows previous studies which have used similar idealised scenarios to understand dry ³ as well as as moist ⁴ atmospheric convection. 

The model is studied for its dynamical response and scaling for varying boundary conditions and input parameters such as the strength of the radiative cooling, the steepness of the lapse rate and the latent heat of condensation to better understand the interaction between moist convection and radiative cooling in the atmosphere. We also compare the convective organisation in our simplified model with more complex cloud-resolving atmospheric simulations ⁵. 

References:

1. G. Ahlers, S. Grossmann, and D. Lohse, “Heat transfer and large scale dynamics in turbulent Rayleigh-Bénard convection,” Reviews of modern physics, vol. 81, no. 2, p. 503, 2009.

2. G. O. Hughes and R. W. Griffiths, “Horizontal convection,” Annu. Rev. Fluid Mech., vol. 40, pp. 185–208, 2008.

3. M. Berlengiero, K. Emanuel, J. Von Hardenberg, A. Provenzale, and E. Spiegel, “Internally cooled convection: a fillip for philip,” Communications in Nonlinear Science and Numerical Simulation, vol. 17, no. 5, pp. 1998–2007, 2012

4. G. K. Vallis, D. J. Parker, and S. M. Tobias, “A simple system for moist convection: the rainy–bénard model,” Journal of Fluid Mechanics, vol. 862, pp. 162–199, 2019

5. C. J. Muller and I. M. Held, “Detailed investigation of the self-aggregation of convection in cloud-resolving simulations,” Journal of the Atmospheric Sciences, vol. 69, no. 8, pp. 2551– 2565, 2012.

Acknowledgement - This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 101034413.

How to cite: Agasthya, L. and Muller, C. J.: Dynamics and scaling of moist, internally cooled convection, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6095, https://doi.org/10.5194/egusphere-egu23-6095, 2023.

How to cite: Rauterkus, R. and Maronga, B.: Large-eddy simulations analyzing the impact of RV Polarstern on surrounding measurements during MOSAiC, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14855, https://doi.org/10.5194/egusphere-egu23-14855, 2023.

The LES-based PALM model system 6.0 is a state-of-the-art atmospheric numerical model widely used among scientists for urban boundary layer and urban climate studies. Despite being subjected to many validation and sensitivity studies which tested the model’s accuracy and applicability to urban environments, a major step is needed to test its sensitivity to different driving conditions.

In this study, we performed a series of PALM model simulations for a given domain and two selected episodes during the year 2019. Each simulation lasts 72 h, and all of them were performed for an 8 km x 8 km domain in 10 m resolution encompassing a real built-up residential area in the southeast part of the city of Prague, Czech Republic. The simulation setups are identical apart from  the initial and boundary conditions imposed. For that purpose we utilized the mesoscale WRF model and created an ensemble consisting of several members with different parameterization schemes.

This study's findings are serving to better understand how different initial and boundary conditions affect the PALM model simulations. In addition, we present the process, complexity, and challenges one can encounter while trying to find the optimal set of initial and boundary conditions for a given PALM model simulation. Moreover, the performed simulations have shown that most of the variance in the ensemble comes from the driving conditions. 

How to cite: Radovic, J., Belda, M., Resler, J., Krč, P., Eben, K., Bureš, M., and Geletič, J.: Sensitivity study of the PALM model system to different driving conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11730, https://doi.org/10.5194/egusphere-egu23-11730, 2023.

Spring frost has been recognized as the most harmful weather hazard for agriculture. One way to fight it back is using a wind machine - a 6-m diameter blowing fan atop a 10-m mast. It rotates on itself in approximately 4min30s and blows a slightly positive air using the strength of the nocturnal thermal inversion to mix cold air near the ground with warmer air above. Previous studies have focused on the protection area of the wind machine under different weather conditions or propeller designs. However, while weather conditions are undergone and field measurements are sparse, effects like the topography, the synergy between devices, or the addition of a burner are hard to catch and separate and are, therefore, not yet well understood.

In this study, we present field measurements dedicated to the future calibration of a computational fluid dynamics model (PALM) involving an actuator disk to simulate a wind machine operating during radiative frost conditions. This numerical model will aim to understand better such tower's external effects, for which field measurements are challenging to implement.

To characterize the jet of the propeller at the onset, vertical profiles were measured with a 3D sonic anemometer at high frequency (100Hz) 10 m away from the wind machine every meter between 3 and 15 m heights. Mass flow and momentum rates of about 500m3/s and 5000N were deduced for some different designs of wind machines.

To characterize how the jet interacts with the ground regarding the distance from its source, 2D sonic anemometers were placed in a row in front of the wind machine. Results highlight three different zones where the jet behaved distinctively:

• A dead zone, where the jet passed over the ground (0 to 30 m away from the WM);
• An impact zone where the jet directly hit the ground with maximum velocity (40 to 60m away from the WM);
• A spreading zone where the protection mixing was due to eddies spreading in the inter-rows and breaking into smaller eddies in contact with posts and vine plants (70m away from the WM and beyond). As the distance from the machine increased, the jet velocity decreased before vanishing.

From these results about the onset condition and development of the jet, it will be possible to tune the rotating actuator disk to reproduce with PALM (an LES meteorological-oriented modeling system) an acceptable behavior of the flows (gust and weather interacting with the ground) despite several simplifications of the underlying physics.

While calibrations are still ongoing, the first results are encouraging, whether it be on a wind machine in a free environment or with the reproduction of a radiative night situation. The primary analysis will focus on the animation of state variables to assist in analyzing statistical results on field measurements. As little knowledge is available about the combined use of a burner with a wind machine, several strategies for a burner location will be tested in order to initiate a research topic that the authors believe is currently unexplored.

How to cite: Le Cap, C., Carlier, J., Katurji, M., Lin, D., Quénol, H., Georgeault, P., Buisson, E., and Heitz, D.: Towards numerical simulation of a wind machine during spring frost calibrated with field measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1425, https://doi.org/10.5194/egusphere-egu23-1425, 2023.

The Atmospheric Boundary Layer (ABL) has always played a critical role in determining global aerosol dispersion and distribution in the atmosphere. Absorbing aerosols constituting of black carbon (BC) influences our atmosphere in several ways which includes absorption of the incoming solar radiation. There have been several studies on the spatio – temporal heterogeneity of aerosols over the North Eastern Region (NER) of India but very few studies exist on the vertical distribution of aerosols till date. To fill this gap, Microaethalometer (MA), Optical Particle Counter (OPC) and Dr. Pisharoty Radiosonde (sonde) has been deployed using tethered balloon up to 1 kilometre altitude on campaign mode for the first time in NER of India for characterization of airborne aerosols and meteorological parameters. The experiment was conducted successfully over a high altitude station in Meghalaya, Umiam (25.67 ^oN, 91.91^o E, 1040 m amsl) during winter, pre monsoon and post monsoon seasons of the year 2019 and over 3 stations viz., Dhubri (26.02° N, 89.97° E, 31 metres), Guwahati (26.10° N, 91.60° E, 55 metres), and Dibrugarh (27.47° N, 94.91° E, 108 metres) along the Brahmaputra valley in Assam, India during the winter and pre monsoon seasons of the year 2021. Meteorological balloons were also launched simultaneously 4-5 times per day in each of these 3 stations for one day during the time of tethered balloon launch. Distinct diurnal variability has been observed in the vertical profiles of BC and meteorological parameters throughout the day. In the absence of incoming solar radiation or weak turbulence i.e. during the morning, evening and night time the ABL height (ABLH) measured by sonde varied from 75 – 200 m, 50 – 150 m, 100 – 275 m and 50 – 225 m during winter season over Umiam, Dhubri, Guwahati and Dibrugarh respectively. While during pre monsoon season, ABLH varied from 50 – 200 m, 75 – 250 m, 125 – 250 m and 50 to 250 m respectively over the 4 stations. Near surface BC concentration (BCC) was found to be high within the ABL during morning, evening and night time over all the stations. During winter and pre monsoon, maximum BCC reached up to approximately 9 µg/m³, 30.98 µg/m³, 22.16 µg/m³, 13.01 µg/m³ and 5 µg/m³, 9.65 µg/m³, 13.6 µg/m³, 6.4 µg/m³ respectively over Umiam, Dhubri, Guwahati and Dibrugarh near to the surface. ABLH goes above 1 km during day time, where the rapid development of a well mixed vertical profile of BC was observed during the day over the study sites. The vertical profiles of BC also showed multiple elevated layers in some stations which closely followed the vertical profiles of the meteorological parameters.

How to cite: Gogoi, M., Borgohain, A., Kundu, A., Kundu, S. S., Bhuyan, P. K., Pathak, B., Bhuyan, K., Barman, N., Banik, T., Charri, A., Chakravorty, A., Kumar, P., Chanda, R., Raju, P. L. N., Srivastava, A., Gogoi, R. B., and Aggarwal, S. P.: Atmospheric Boundary Layer and the Vertical Distribution of Black Carbon over Plain and Hilly Terrain of North East India using In Situ Measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-350, https://doi.org/10.5194/egusphere-egu23-350, 2023.

Summer Shamal, a strong low-level northwesterly wind in the Middle Eastern region, is the major trigger for dust storm activity with a broad impact on regional transport and human safety. Due to the scarcity of high-frequency data, near-ground turbulent mixing analyses under Shamal are still rare. The current study investigates the near-surface turbulence characteristics of the atmospheric boundary layer (ABL) in the coastal region of Qatar under summer Shamal conditions (26.08 N, 51.36 E). The results show that, in the absence of monsoon, Shamal prevents the development of summer sea breezes in the Persian Gulf. Compared to non-Shamal days (NSD), Shamal days (SD) are characterized by higher sensible heat flux magnitude and turbulent kinetic energy (TKE) with lower humidity, especially around noon time. Turbulence stability analysis indicates the probability of different dust activities during summer SD and NSD. Wind velocity spectra are investigated to evaluate the TKE dissipation rate. A Weibull distribution is observed for PDFs of TKE dissipation rate under SD for both stable and unstable conditions.

How to cite: Li, Y. and Sadr, R.: Atmospheric Turbulent Characteristics under Summer Shamal in Coastal Qatar, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4115, https://doi.org/10.5194/egusphere-egu23-4115, 2023.

The atmospheric stability condition in the coastal region of Qatar are analyzed using the measurements conducted on the shoreline (26.08N, 51.36E). The micrometeorological data are collected, from August 2015 to September 2016, using sonic anemometers (20 Hz) at three heights and a weather station on the top of a 9 m tower. Two different atmospheric daily stability patterns, ‘orderly’ and ‘disheveled’, are identified based on the wind conditions. A day is classified as ‘orderly’ if the amount of wind from the sea lasts less than 10% of the day. Otherwise, a day with an onshore wind of more than 10% is considered ‘disheveled’. The orderly stability pattern shows a daily descending and ascending trend during the sunrise and sunset periods, respectively, while the disheveled days follow a random pattern with no clear order. The probability distribution of the stability parameter shows a narrower distribution for the ‘orderly’ days, containing fewer unstable periods than the ‘disheveled’ days. The chaotic trend during disheveled days could be caused by the inhomogeneity of the roughness between the land and the sea (1000 times). The integral length scales are further investigated to clarify the influence of the local thermally forced flow to the disheveled patterns.

How to cite: Sadr, R. and Li, Y.: Two daily stability patterns in the atmospheric surface layer of the coast of Qatar, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4130, https://doi.org/10.5194/egusphere-egu23-4130, 2023.

Fog is a difficult meteorological phenomenon to predict due to its high spatial and temporal variability and the complexity of physical processes and their interplay. In this context, the SOFOG3D field campaign, which took place during winter 2019/2020 over the Landes region in the South-West of France, provides a 3D mapping of the boundary layer during fog events. It aims to advance our understanding of fog processes in order to improve forecasts of fog events by numerical weather prediction (NWP) models.

The present study focuses on three days between 28 and 30 December 2019 characterized by different fog life cycles between two sites about 100 km apart. In situ and remote sensing measurements, such as microwave radiometer and cloud radar, show that on the supersite a radiative fog that occurred the first night lifted into a stratus in the morning remained all day long, and lowered in the afternoon to form a new fog by stratus lowering. In contrast at the Agen site, the stratus completely dissipated and a radiative fog formed the second night. The widespread radiative fog over the entire domain during the first night developed due to cold air advection from the East. We conduct data analysis to study why the stratus lowering is generalized over the northern part of the domain, while the stratus completely dissipates over the southern part of the domain.

This analysis is complemented by a 3D numerical simulation performed with the Meso-NH model applied at 100 m resolution with a downscaling approach from the operational AROME model, using the LIMA 2-moment microphysical scheme with a prognostic representation of a multimodal aerosol population. Preliminary results show that for the second night, the simulation well reproduces the contrasting fog life cycle for both sites with radiative fog on Agen and stratus lowering on the supersite but forming earlier fog on the former.

A budget analysis is conducted to investigate the spatial heterogeneity of this fog event at the regional scale and to study the physical mechanisms involved in fog formed by stratus lowering that remains especially difficult to forecast by NWP models.

How to cite: Fathalli, M., Lac, C., and Burnet, F.: Fog formed by stratus lowering: an observational and modeling case study from the SOFOG3D field campaign, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14885, https://doi.org/10.5194/egusphere-egu23-14885, 2023.