We demonstrate that we can measure spectral coherence of offshore atmospheric turbulence at heights and with lateral displacements relevant for dynamic loads on modern, large wind turbines. This is done by five coordinated, pulsed Doppler lidars standing on the coast of the North Sea with beams intersecting almost perpendicularly. The six crossing points are 150 to 250 m above the ocean and have lateral separations of up to 200 m, reflecting the scale of modern offshore wind turbines. We compare the measurements with spectral and cross-spectral models. The model of Syed and Mann (Boundary-Layer Meteorology, 2024, vol 190), in general fits the spectra well and predicts the lateral coherences well. However, there are cases where the measured lateral coherence of the v-component is much larger than predicted. This seems not to be due to malfunction of the instruments, but rather due to non-turbulence processes in the atmosphere, e.g . interval gravity waves. We will also touch upon the potential consequences for loads on wind turbines.
How to cite: Mann, J., Patel, A., and Sjöholm, M.: Experimental determination of offshore turbulence spectra and lateral coherences with multiple lidars, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3520, https://doi.org/10.5194/egusphere-egu25-3520, 2025.
Evening Transition (ET) over Kempegowda International Airport (77.70◦ E, 13.20◦ N) is investigated over 2
seasons to calculate robust statistics of decay of Turbulent Kinetic Energy (TKE) in the Atmospheric Boundary
Layer (ABL). Although previous research on TKE decay during ET has largely relied on Large Eddy Simulations
(LES) and analytical models to determine decay rates of volume-averaged TKE, our study takes a more granular
approach.
We use two remote sensing instruments (Radiometer Physics HATPRO Radiometer and Vaisala Windcube
100S) to measure temperature, humidity, and wind components at multiple levels within the ABL. In addition,
ground instruments like temperature, relative humidity sensors, ground heat flux sensors and radiation sensors
provide near-surface data about temperature, moisture and heat fluxes. Together, these instruments allow us
to track local decay of TKE at various heights within the ABL.
We then apply functional fits for various time intervals during the decay period, generating vertical profiles
of the TKE decay exponents across the ABL. These profiles provide valuable insights into the relative importance
of surface-driven vs. ABL top-driven decay of TKE. Moreover, we observe that separate intervals of time in the
ET might have separate functional forms for the decay of TKE, instead of a commonly used single power-law
fit. The entire investigation enhances our understanding of TKE decay during the ET and could be
helpful for real-life applications such as understanding nighttime pollution dispersal or forecasting condensation
phenomenon like fog or mist. around Bengaluru city.
How to cite: Banerjee, S., Pratap Singh, S., and Kr, S.: Decay of Turbulence during Evening Transition at the Kempegowda International Airport, Bengaluru, India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2036, https://doi.org/10.5194/egusphere-egu25-2036, 2025.
Turbulent fluxes are critical in atmospheric science and are typically calculated using the eddy covariance system. However, the presence of motions of larger scale and biases from observational instruments often affect the accurate procurement of turbulent fluxes. To mitigate the influence of non-turbulent motions, data from multiple observational stations under various stratification conditions are analyzed. From these data, several new aspects of characteristics of atmospheric turbulence can be defined and investigated from statistical points of view, such as the properties of transport, the fractal dimension, and the anisotropy. Based on Hilbert–Huang transform, these novel characteristics can be analyzed across different scales and tested to be scale-dependent with stable patterns. However, for individual cases, it happens that these stable pattern are violated at comparatively large scales, indicating the existence of non-turbulent motions. Identifying these outliers enabled their elimination and the reconstruction of turbulence data, which reveals that the presence of non-turbulent motion leads to an overestimation of turbulent fluxes. The degree of overestimation depends on several predefined properties of non-turbulent motions, such as monotonicity, complexity, and intensity. Therefore, these novel characteristics enable the quantification of turbulent transport with higher precision and a broader application scope, and further reveal the promise in the simulation of atmospheric turbulence and the parameterization in meteorological and climate models.
How to cite: Liu, Z. and Zhang, H.: Reconstructing atmospheric turbulence from its novel characteristics for high-precision turbulent flux estimates, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1163, https://doi.org/10.5194/egusphere-egu25-1163, 2025.
Turbulence intermittency is a challenge facing in the ffeld of atmospheric boundary layer (ABL) and micrometeorology. We employed an automated algorithm for the separation and reconstruction of Sub-Mesoscale and Turbulent motions (SMT) to examine the basic characteristics of turbulence intermittency driven by submesoscale motion over the complex underlying surface of the Loess Plateau. The ffndings revealed that submesoscale motion has a signiffcant inffuence on turbulence statistical parameters. We analyzed ffve cases and found that the turbulent intermittency events were characterized by quiescent and burst periods. During the quiescent (burst) period, the turbulent transport weakened (strengthened), turbulence ffuctuations weakened (strengthened), atmospheric stability increased (decreased), and turbulent energy decreased (increased). These bursts can be triggered by energy conversion from sub-mesoscale to turbulent motion. Actual observations revealed atmospheric conditions where turbulent intermittency events are more likely to occur: wind speed U < 3.5 ms − 1 , wind speed gradient ΔU/ΔZ < 0.2 s − 1 , temperature gradient ΔT/ΔZ > -5.1 K/100 m, or bulk Richardson number Rib > -0.1. The inffuence of turbulence intermittency on the classical energy non-closure issue over the Loess Plateau was explored further. The results show that the presence of sub-mesoscale motions contributed to energy closure, with an energy closure of 78 % during daytime and 36 % during nighttime. And different periods of turbulent intermittency events affected energy non-closure differently, the energy closure during the burst (quiescent) period was approximately 98 % (70 %) during daytime and 68 % (17 %) during nighttime, approaching closure and far exceeding the overall closure rate during the burst period, whereas signiffcantly low during the quiescent period. This suggests that turbulence intermittency is a very important factor causing energy non-closure over complex underlying surfaces, especially in stable boundary layer (SBL) during nighttime. The results are highly signiffcant for a better comprehension of turbulence intermittency and surface-atmosphere interactions over complex underlying surface.
How to cite: Chang, H., Ren, Y., and Zhang, H.: The characteristics of turbulence intermittency and its impact on surface energy imbalance over Loess Plateau, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2131, https://doi.org/10.5194/egusphere-egu25-2131, 2025.
Street canyons are a common feature in many urban environments. They are also arguably the most polluted region of the urban boundary layer due to the presence of heavy traffic and limited penetration of fresh wind for ventilation. Hence a detailed understanding of the processes taking place within the canyon is crucial to ensuring good air quality in urban areas. In this study, we investigate the turbulent flow and pollutant dispersion in four model street canyons having different morphologies, by conducting time-resolved particle image velocimetry (PIV) measurements in a wind tunnel. The street canyons analysed have different aspect ratios (the ratio of the height of the street canyon to its width) and were surrounded by higher or lower buildings, i.e. by street canyons with a higher or lower aspect ratio. First, we introduce an approach for determining pollutant concentrations from PIV data and show that the method can be reliably used to measure the planar pollutant fluxes. Differences in the concentration and flow fields at different planes were observed, thus indicating the importance of considering the three dimensionality of the canyons. The turbulent scalar flux was found to play a dominant role in pollutant transport at the roof level for canyons surrounded by buildings having the same aspect ratio as the canyon. Conversely, advection dominates at roof level when a canyon is surrounded by buildings having different aspect ratios. Quadrant analysis of the momentum and scalar flux reveals high correlations between ejections and sweeps and ventilation processes at the roof level. We apply the dynamic mode decomposition (DMD) technique, a data-driven algorithm, to extract dynamically relevant coherent structures of the flow and pollutant concentrations from the data. The results of DMD show that roof and ground level coherent structures play a crucial role in the ventilation of the street canyons.
How to cite: Owolabi, B. and Nosek, S.: Flow and Pollutant dispersion from a line source in 3D urban street canyons having different spatial morphologies, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9201, https://doi.org/10.5194/egusphere-egu25-9201, 2025.
Advection of marine stratocumulus clouds (SCu) from the South East Pacific into the Atacama Desert forms large and semi-permanent fog banks at the top of the coastal mountain range. These fog banks are the sole water input for xeric ecosystems and represent a freshwater resource to be harvested by local communities in the driest place on Earth. The fog maintenance depends on the marine boundary layer (MBL) thermal inversion, which results from the equilibrium between subsidence and ocean heat fluxes. To study these interactions, we performed a field experiment in July 2024 in North West Chile called StraToFog, to measure surface and airborne boundary layer state during the SCu-fog transition. Surface measurements of energy balance fluxes and vertical observations of MBL thermodynamics were performed over a transect following the SCu-fog transition: at the ocean, the top of the mountain range, and inland in the desert. To complement these measurements, a high-precision balance and a standard fog collector transect were installed to measure fog and dew collection. Overall, our experiment reveals two distinctive fog regimes, which depend on the interplay between MBL growth, the strength of subsidence and the development of a sea breeze that pushes the MBL with clouds onto the coastal mountain range. First regime occurs at night when inversion layer is controlled by low surface temperature, resulting in air saturation under lower humidity content (↓es), leading to fog collection ~0.5 L m-2 h-1. The second regime occurs after a dissipation break at noon, where MBL advection increases humidity leading to air saturation under higher air temperatures (↑e), resulting in fog collection ~3 L m-2 h-1. Our results show a SCu top uplift between 150 to 400 m from ocean to inland. This uplifting is explained by the abrupt topography (800 m height; 5 km long) and by the sensible heat flux increases from 32 W m-2 over the ocean to 250 W m-2 over land. Airborne measurements show a diurnal cycle of fog cloud formation, which show a thickness of 20 m in the morning, grow to 200 m at noon, dissipate in the afternoon, and form again up to a thickness of 100 m during the evening. In addition, a very strong inversion layer (~18 K) was observed at the top of the cloud layer at 08:00 LT. The surface soil balance experiment shows a weight increase at night (00:00-06:00 LT) under clear sky conditions, associated with dew deposition. In contrast, during foggy days, the soil weight increases in the morning (06:00-12:00 LT) under windless (<1 m s-1) conditions, followed by a decrease in the afternoon under windy conditions (>4 m s-1), associated with fog deposition/evaporation. Further analysis of this data, accompanied by high resolution numerical simulations, will allow us to better understand fog dynamics in drylands and its potential prediction.
How to cite: Lobos-Roco, F., Espinoza, V., Keim-Vera, K., Munoz, F., Suarez, F., and Hartogensis, O.: Marine boundary layer evolution in the transition from low stratocumulus clouds to land fog in the coastal mountains of Atacama, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9850, https://doi.org/10.5194/egusphere-egu25-9850, 2025.
Structures and processes in the atmospheric boundary layer (ABL) span a wide range of scales which cannot be fully captured by a single measuring technique. Doppler lidars are a preferred remote sensing tool for the observation of wind profiles in the entire ABL. Typically the relevant scales of ABL flow structures increase with increasing distance from the surface.
While pulsed Doppler lidars (PDLs) are typically sufficiently sensitive to reach the top of the ABL, they leave an unobserved gap in the lowest 50 m. This is because the PDL receiver doesn’t work before the transmit pulse has left the lidar. In addition to the gap, the spatial resolution δr, which is proportional to the pulse length l, is not always satisfying in the lowest range gates, since wind gradients occuring over canopies, urban surface structures or in case of stable stratification cannot be resolved reliably. l cannot be deliberately shortened for the sake of velocity resolution δv and sensitivity s (δv ∝ l-1, s ∝ l).
Continuous wave lidars (CDLs) are typically restricted to a maximum height of 200 m. The ranging is here achieved by focusing the beam. With this technique the range resolution δr is not constant but becomes finer the shorter the range r. At r = 10 m, a range resolution δr = few centimeters is possible. Since δr ∝ r2 the resolution at 200 m is no longer superior to that of PDLs. Thus, a CDL is a perfect complement to a PDL in order to observe near-surface structures of the ABL.
We will present observations obtained with a PDL-, CDL-combination. Both systems are using an identical scanning cone with a zenith angle of 10°. This scan geometry is particularly suitable for operation close to obstacles as trees or buildings, in urban environments or in complex terrain.
How to cite: Burgemeister, F., Markmann, P., and Peters, G.: Seamless wind profiling of the atmospheric boundary layer, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11181, https://doi.org/10.5194/egusphere-egu25-11181, 2025.
In a stable boundary layer (SBL), turbulence is generally weak and exhibits significant intermittent characteristics. Interactions among motions of different scales complicate its structural evolution, making it difficult to predict. This study focuses on two typical processes in the SBL: Low-Level Jet (LLJ) and Internal Gravity Waves (IGWs), investigating how their interactions influence the evolution of turbulence structures. Utilizing a full boundary layer turbulence observation and data processing system at Zhongchuan International Airport, this study includes eddy covariance system, Doppler Lidar, and wind profiling radar. In a strongly SBL, turbulence energy accumulates in higher layers and, during downward transfer, generates local LLJ and IGWs, triggering intermittent turbulence events. The internal factors of turbulence intermittency dominated the process. The interaction between LLJ and IGWs maintains intermittent turbulence burst, accompanied by the conversion of sub-mesoscale energy to turbulent energy. In a weakly SBL, the conversion of sub-mesoscale motion energy drives intermittent turbulence events, along with energy transfers between different scales of IGWs, resulting in weaker turbulence intermittency. The external factors of turbulence intermittency dominated the process. In both cases, the interaction between LLJ and IGWs alters turbulence structure and atmospheric stability. Turbulent mixing changes the mean gradient field, further influencing the LLJ height. This study elucidates the mechanisms of interaction between internal and external factors in turbulence intermittency. It outlines energy transfer among different scales of motion and clarifies the mechanisms behind state transitions and structural evolution of strongly and weakly SBL. These findings are significant for advancing theoretical research and simulation developments of the SBL.
How to cite: Ren, Y., Ding, J., and Zhang, H.: Mechanism of Turbulence Structure Evolution in the Nocturnal Boundary Layer during the Interaction of Low-Level Jet and Internal Gravity Waves: Based on Full Boundary Layer Turbulence Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1995, https://doi.org/10.5194/egusphere-egu25-1995, 2025.
Reynolds stress anisotropy is one of the fundamental characteristics of all wall bounded turbulent flows, especially those in the atmosphere. In canonical (flat and horizontally homogeneous) boundary layers, the anisotropy presents a balance between the processes that generate it (shear, buoyancy and wall blocking) and the pressure-redistribution terms that act to redistribute turbulent kinetic energy towards the non-energetic velocity components. This pressure redistribution remains an area of active research, especially in stratified conditions, dominating the atmospheric surface layer.
Here we use observations from four turbulence towers in flat and horizontally homogeneous terrain to explore the evolution of anisotropy as the stratification becomes increasingly unstable. We identify three regions that can be roughly related to dynamic, convective-dynamic, and convection regimes, and show which processes, including turbulence organization into coherent structures, dominate anisotropy in each region, and particularly what is the role of rapid pressure-redistribution terms in driving the decrease of wall-normal and increasing spanwise variance in the dynamic-convective region.
How to cite: Stiperski, I. and Katul, G. G.: Energy anisotropy, turbulence organization and the role of pressure-redistribution in near-surface unstably-stratified turbulence, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16649, https://doi.org/10.5194/egusphere-egu25-16649, 2025.
Wind energy is a crucial component of the global energy market due to its minimal environmental impact and continuous technological advancements. Offshore wind energy, characterized by stronger and more homogeneous winds compared to onshore locations, has attracted significant interest from the industry [1]. However, the remote and inaccessible nature of offshore wind farms presents challenges for wind resource assessment. Traditional methods, such as anemometers mounted on masts, are not feasible in these environments. Doppler wind lidars (DWLs) have emerged as a viable alternative, providing cost-effective and flexible measurements of wind vectors at hub-height altitudes. DWL are highly accurate in deteriming the line-of-sight velocity. Despite this, DWLs inherently underestimate or overestimate wind turbulence, a key parameter for wind energy applications, due to the spatial and temporal averaging effect that result from the probe volume and the scanning configuration [2]. This turbulence biase can lead to over-design or increasing loads on wind turbines, significantly increasing costs.
To address this challenge, a DWL and anemometer simulator based on the Mann turbulence spectral model was developed, capable of generating high-resolution synthetic turbulent wind fields using the three Mann model parameters: turbulence length scale (L), eddy life-time parameter (Γ), and turbulent energy dissipation rate [3]. The simulator replicates the IJmuiden offshore meteorological mast (metmast) measuring setup, allowing direct comparisons between DWL and anemometer measurements at a height of 90 m. Turbulence fields were simulated across a wide range of Mann parameter values to cover a wide range of atmospheric turbulence conditions.
The simulation results revealed that DWLs underestimate turbulence up to 50% with respect to anemometers when L approximated 0 m. Conversely, Γ had negligible influence on DWL turbulence measurements. The error in turbulence estimation by DWLs was successfully parameterized by the lturbulence length scale L, drastically reducing computational complexity while maintaining accuracy.
These findings provide a practical framework for correcting DWL turbulence measurement errors, facilitating their application in diverse atmospheric scenarios. Future work will focus on validating the parameterization with experimental data under varied atmospheric conditions and implementing the correction method to improve DWL performance in operational settings. By addressing this limitation, the results advance the reliability of offshore wind resource assessments, contributing to the broader adoption of wind energy solutions.
REFERENCES
[1] Joyce Lee and Feng Zhao, “Global wind report 2018,” Tech. Rep., Global Wind Energy Council, Apr. 2019.
[2] A. Peña, G. G. Yankova, and V. Mallini, “On the lidar-turbulence paradox and possible countermeasures,” Wind Energy Science, vol. 10, no. 1, pp. 83–102, 2025.
[3] Jakob Mann, “Wind field simulation,” Probabilistic Engineering Mechanics, vol. 13, no. 4, pp. 269–282, 1998.
ACKNOWLEDGEMENTS
This research is part of the project PID2021-126436OB-C21 funded by Ministerio de Ciencia e Investigación (MCIN)/Agencia Estatal de Investigación (AEI)/ 10.13039/501100011033 y FEDER “Una manera de hacer Europa” and part of the PRIN 2022 PNRR, Project P20224AT3W funded by Ministero dell’Universit`a e della Ricerca. The European Commission collaborated under projects H2020 ATMO-ACCESS (GA-101008004) and H2020 ACTRIS-IMP (GA-871115).
How to cite: Salcedo-Bosch, A., Rocadenbosch, F., Lolli, S., Mann, J., and Peña, A.: Parameterization of the Turbulence Averaging Error by Doppler Wind Lidars: a Simulator Approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18484, https://doi.org/10.5194/egusphere-egu25-18484, 2025.
Measurements of wind and turbulence variables have been performed for decades by means of ultrasonic anemometers (sonics), which have proven to be a reliable, cost-effective and accurate measurement technique for both operational and scientific applications. Sonics are using short ultrasonic pulses transmitted between transducers along different measuring paths to retrieve the 3D wind information. While the measurement principle of commercially available sonics follows comparable technical approaches a variety of sensor head geometries and path arrangements are used in order to minimize potential constraints in accuracy. Two main aspects have to be regarded here, a shadow effect appearing lee wards of each transducer element and a flow distortion caused by individual structures of sensor heads. Furthermore, the arrangement of the measuring paths determines the responsiveness of the sensor to specific wind components. For studies in the atmospheric boundary layer typically the vertical wind component is of highest interest. In order to address these various requirements with one system, trade-offs are unavoidable. The Multi-Path approach for sonics allows to establish redundant 3 x 3 measuring paths involving only six transducers. Depending on the inflow angle such overdetermined system of simultaneously measured radial winds allows to select measuring paths with minimized impact from shadowing and flow distortion for data retrieval. Three of these measuring paths are aligned vertically, providing three independent measurements of the vertical wind.
A six-month comparison of five sonic types was performed in northern Germany at an abandoned airfield with a homogenous surface. We will present derived time series of wind and comprehensive turbulences variables including vertical turbulent fluxes of heat and momentum also covering periods of different weather types, e.g. precipitation events. We focus on the sonic similarities and differences, which are also relevant if standardisation of techniques and data retrievals are considered, without discarding technical improvements such as the Multi-Path technology.
How to cite: Kirtzel, H.-J., Burgemeister, F., and Peters, G.: Wind and turbulence measurements with different sonic sensor head geometries, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18608, https://doi.org/10.5194/egusphere-egu25-18608, 2025.
Fog is a highly complex weather phenomenon influenced by numerous factors. This study aims to investigate the impact of Changbai Mountain topography on the formation and development of the spring fog in the Bohai Sea. From May 12 to 14, 2021, the Bohai region experienced a sea fog event. Utilizing the Himawari-8 satellite retrieval data, the European Centre for Medium-Range Weather Forecasts (ECMWF) 5th Generation ERA5 reanalysis dataset, land and sea station observations, the WRF model, the topography sensitivity experiment, and the backward trajectory tracking, a study was conducted to assess the influence of Changbai Mountain topography on the evolution of the Bohai sea fog. The results indicated that the Changbai Mountain topography significantly impacted the propagation and concentration of the Bohai sea fog through the dual effects of Venturi Effect and Foehn Clearance Effect. Comparative simulations incorporating and excluding the Changbai Mountain revealed that its topography favored weak convergence (Venturi Effect) of low-level airflow in the Bohai Sea induced by a high-pressure system, promoting westward fog expansion. Additionally, the backward trajectory further indicated that the Foehn Clearance Effect of Changbai Mountain extended its influence far beyond the immediate lee side, contributing to significant changes in atmospheric conditions such as reductions in relative humidity and increases in potential temperature. The dry, warm foehn contributed to a reduction in the liquid water content, ultimately leading to the weakening or even dissipation of the sea fog in the region close to Changbai Mountain. This study emphasizes the crucial role of Changbai Mountain topography in the development and evolution of fog, providing valuable insights for forecasting fog in complex terrain.
How to cite: Tian, M.: Impact of Changbai Mountain Topography on the Spring Fog over the Bohai Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2863, https://doi.org/10.5194/egusphere-egu25-2863, 2025.
Detailed convective boundary layer (CBL) structure and the impact factors over the Tibetan Plateau has not been clearly understood, particularly for the level of neutral stability (zn), at which statically unstable lower CBL begins to transit into slightly stable upper CBL. Substantial uncertainties still exist in numerical models with different planetary boundary layer (PBL) schemes to reproduce such detailed structure. In this study, detailed CBL structure and processes over the Tibetan Plateau are examined using multi-year radiosonde data and large-eddy simulation (LES), particularly focusing on the impact of surface heating and entrainment on zn. The results indicated that the values of zn spatially ranged within 0.16–0.38zi on the plateau, with zi representing the CBL depth, and zn was higher in the southwestern region and lower in the southeastern region. Surface-/entrainment-induced large-scale thermals (corresponding to nonlocal fluxes) tended to suppress/elevate zn, due to warm turbulence penetrating into the upper/lower CBL, whereas small-scale eddies (corresponding to local fluxes) played an opposite role on modifying zn. The LES results suggested that zn increased before 08:00 Local Time (about 80 minutes after sunrise) because surface-induced small eddies dominated during the early stage of CBL growth and zn decreased afterwards as large-scale surface-induced thermals became more active. These improved understanding provides guidance for further improvement of PBL schemes.
How to cite: Li, X., Hu, X.-M., Wei, W., Zhang, L., Ren, Y., and Zhang, H.: Impact of surface and entrainment heat fluxes on the thermodynamic structure of the convective boundary layer over the Tibetan Plateau: observations and modelling analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2021, https://doi.org/10.5194/egusphere-egu25-2021, 2025.
Regional fires result in large emissions of pollutants that can be transported through the atmosphere and impact air quality in remote regions. Studying regional fire aerosol transport is essential to understanding and forecasting air pollution events in different urban centers worldwide. However, there is a lack of research analyzing atmospheric patterns and mechanisms during regional fire aerosol transport events in tropical regions with complex topography. We investigate atmospheric conditions during regional fire aerosol transport events in the Aburrá Valley, a mountainous and highly urbanized region in the Colombian Andes. We combine observational and modeling approaches, including reanalysis data, high-resolution meteorological simulations, remote sensing information, and ground-based stations. Initially, regional transport events were selected from information from a Black Carbon monitor and verified using back-trajectories and hotspots data from MODIS. Besides, we performed two-month (February and March) 1-km resolution meteorological simulations with WRF model simulations for five years (2020-2024) to identify characteristic mesoscale patterns during aerosol transport events. Subsequently, we used information from a wind profiler radar, a microwave radiometer, and a series of sonic anemometers to study the incidence of polluted air masses in the local boundary layer. Our results show a notable reduction in precipitation both at a regional scale and in the path of air mass trajectories during regional transport events. Anomalous northwesterly regional winds are characteristic at low levels, and east-southeasterly winds dominate at mid-levels. At a local scale, these regional winds are channeled from the north and katabatic winds are intensified during night and early morning, leading to vertical wind shear within the boundary layer. These conditions favor the generation of mechanical turbulence during the night, enhancing the mixing of external pollutants towards the valley surface. Our study advances the understanding of mechanisms related to the impact of regional fire events on Aburrá Valley’s air quality, which can become more frequent under climate change conditions. Besides, these results contribute to the improvement of forecasting systems in the region, which is essential for comprehensive air quality management.
How to cite: Hernández, K. S., Espinosa, D., Ayala-Parra, G. A., Montoya, P. A., Ceballos, L. I., Zuluaga, M. D., Orrego, A. Z., and Ramírez, M.: Investigating atmospheric mechanisms behind the long-range transport of fire aerosols: from the regional free atmosphere to the local boundary layer in a narrow valley, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-493, https://doi.org/10.5194/egusphere-egu25-493, 2025.
Quantifying the effects of stratocumulus cloud feedbacks remains a key challenge, particularly due to the complex interactions between the boundary layer and the cloud top that occur at meter and submeter scales. Droplet sedimentation counteracts cloud-top entrainment by moving droplets away from the warm, dry free troposphere, thereby decreasing cloud-top evaporation and turbulence generation. Assessing how sedimentation influences entrainment and turbulence is essential for determining cloud lifetimes.
Previous works using large-eddy simulations (LES) with 5-10 m resolution demonstrated that sedimentation reduces the mean entrainment velocity (Ackerman 2004, Bretherton 2007, Hill 2009). However, the strength of this reduction remains uncertain because insufficient resolution introduces spurious upward fluxes that oppose the sedimentation flux. Local direct numerical simulations (DNS) studies, focused exclusively on the cloud layer at submeter-scale resolution, reported a reduction of the mean entrainment velocity due to sedimentation of up to 40%, or 3 times higher than LES results (de Lozar 2017, Schulz 2019). The question then remains: do these results also hold when considering the full vertical domain of the stratocumulus-topped boundary layer, spanning from the surface level to the free troposphere?
The novelty of this work lies in using DNS to simulate meter-scale processes at the cloud top, while encompassing the full vertical extent of the stratocumulus-topped boundary layer. We perform sensitivity experiments that involve changing the sedimentation strength and the Reynolds number. Consistent with previous studies, we find that sedimentation reduces the mean entrainment velocity by at least 20%, with the magnitude increasing for higher Reynolds numbers. Interestingly, the turbulence kinetic energy and the turbulent entrainment flux also increase with sedimentation.
To resolve this apparent contradiction, we quantify the mean fluxes of the liquid water static energy at the cloud-top region. Our results show that the magnitude of the sedimentation flux undergoes a more rapid growth than the turbulent flux with sedimentation, effectively compensating for the increase in the turbulent flux. Additionally, the contrast in the vertical velocity between updrafts and downdrafts in the subcloud layer becomes less extreme with sedimentation. The skewness in this region shifts from a predominantly positive profile to a more neutral one. This more balanced distribution of vertical motions results from increased liquid water availability for evaporation in the downdrafts, which in turn accelerates them. In summary, we show that sedimentation effects are as important as turbulent effects at meter-scale resolution. Moreover, sedimentation reshapes the vertical moisture distribution in both cloud and subcloud layers.
How to cite: Pistor, R. and Mellado, J. P.: Droplet Sedimentation Effects in Stratocumulus Clouds, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8194, https://doi.org/10.5194/egusphere-egu25-8194, 2025.
This study evaluates two models for simulating near-field (<200 m) atmospheric dispersion: an operational Lagrangian model, and Computational Fluid Dynamics (CFD) simulations, including Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) approaches. The evaluation is conducted against data from a full-scale atmospheric tracer experiment.
The first model is the Safety Lagrangian Atmospheric Model (SLAM)[1], which implements a Lagrangian stochastic particle dispersion framework coupled with pre-calculated wind and turbulence fields derived from a series of RANS simulations performed with ANSYS Fluent CFD code. On the other hand, the CFD dispersion simulations employ the open-source CALIF3S solver including both RANS and LES methodologies[2] The turbulence closure models correspond respectively to a standard two-equation RANS model and a hybrid RANS/LES approach based on a Detached-Eddy-Simulation (DES) methodology. The full-scale atmospheric dispersion experiment DIFLU (Dispersion du Fluor 18 en Milieu Urbain)[3], provides the validation dataset. The experiment includes tracer concentration measurements under various meteorological conditions within 500 meters of a cyclotron facility.
The results demonstrate that SLAM predicts concentration values comparable to those obtained by CALIF3S-RANS despite the distinct inlet boundary conditions. SLAM uses similarity theory to calculate the inlet velocity, temperature and turbulent profiles, whereas inlet profiles used in CALIF3S are extracted from precursor simulations that best match the measurements. In the near-source region (<50 m), where turbulence plays a significant role, both CALIF3S-RANS and SLAM overestimate the concentration distributions compared to those given by CALIF3S- LES approach. LES results are closer to the measurement because of its advantage in predicting eddy detachments. The disparity of concentration values between RANS and LES diminishes rapidly beyond 100 m from the source, where the region is free of buildings. Overall, SLAM and CALIF3S-LES achieve similar performance in terms of the fraction of simulated values within a factor of two of the measurements under neutral atmospheric conditions. Hence, using RANS simulation is sufficient to achieve acceptable results in the near-field dispersion simulation (<200m) under neutral atmospheric conditions. Nevertheless, more precise results can be achieved with LES method in the near source region (<50m). Future work will focus on other experimental cases, including unstable atmospheric conditions.
[1] S. Yang, I. Korsakissok, P. Laguionie, and P. Volta, “Dispersion du FLuor 18 en milieu Urbain near-field (>200m) atmospheric dispersion simulation and sensitivity analysis following a full scale atmospheric tracer experiment,” in 22nd Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes
[2] J. Janin, F. Duval, C. Friess, and P. Sagaut, “A new linear forcing method for isotropic turbulence with controlled integral length scale,” Phys. Fluids, vol. 33, no. 4, Apr. 2021, doi: 10.1063/5.0045818/1065646.
[3] P. Laguionie et al., “Investigation of a Gaussian Plume in the Vicinity of an Urban Cyclotron Using Helium as a Tracer Gas,” Atmosphere (Basel)., vol. 13, no. 8, pp. 1–16, 2022, doi: 10.3390/atmos13081223.
How to cite: Yang, S., Duval, F., and Korsakissok, I.: Comparison of atmospheric dispersion simulations in the near field (<200) with operational Lagrange model and CFD methods, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17827, https://doi.org/10.5194/egusphere-egu25-17827, 2025.
The influence of surface forcings driven by realistic land cover and surface properties remains underexplored in microscale turbulence-resolving weather simulations, especially within urban settings. Atmospheric models often rely on coarse surface property datasets (typically ranging from 500 m to 10 km), but their low resolution frequently fails to adequately capture critical local surface heterogeneities. Building-resolving large-eddy simulations (LESs) that incorporate detailed land cover and surface characteristics offer a powerful framework for investigating how urban wind speed and turbulence patterns respond to variations in land cover and surface characteristics.
This research examines the significant effects of varying land cover classifications on microscale weather simulations, considering both granularity and resolution, along with other surface characteristics. A series of detailed and comprehensive experiments were carried out for the urban-rural interface of Murcia (Spain) using NCAR-RAL’s GPU-accelerated FastEddy® LES model coupled to WRF. Three case studies over 4-hour periods with distinctive meteorological conditions were used to test different combinations of land use data, roughness length values, urban parametrizations, and driving mesoscale skin forcings. These resulted in a total of 60 LESs with a grid spacing of 10 m spanning a wide range of surface conditions. These simulations incorporated high-quality land cover and soil data, more realistic roughness length estimates, and the implementation of a local terrain smoothing method and a dynamic thermal roughness length parameterization in FastEddy®. These non-standard practices were designed to enhance the skill of the simulations.
The results reveal that configuration details, such as land cover, play a critical role in both mesoscale and microscale simulations, significantly influencing surface fluxes and turbulence generation. While simply increasing the resolution of land cover data produces minimal changes, particularly in rural settings, incorporating more realistic surface property values leads to substantial differences even when resolution remains unchanged. These findings highlight the huge importance of detailed surface characteristics in improving microscale weather predictions.
Acknowledgements: The authors acknowledge the ECCE project (PID2020-115693RB-I00) of the Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación (MCIN/AEI/10.13039/501100011033). ERL thanks her predoctoral contract FPU (FPU21/02464) to the Ministerio de Universidades of Spain.
How to cite: Raluy-López, E., Muñoz-Esparza, D., Montávez, J. P., and Sauer, J.: Enhancing Microscale Urban Weather Simulations: The Role of High-Resolution Land Cover and Surface Characteristics in Turbulence-Resolving LESs for Murcia, Spain, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15494, https://doi.org/10.5194/egusphere-egu25-15494, 2025.
Modeling turbulent air flow accurately is quite difficult, particularly when topographic factors and changing boundary conditions are present. The objective of this research is to combine data from high-resolution Computational Fluid Dynamics (CFD) simulations with a low-resolution meteorological model in order to describe air flow with high accuracy and resolution. To accomplish this, the FLUENT CFD solver was integrated with the widely used Weather Research and Forecasting (WRF) model.
Time-dependent boundary conditions for mesoscale atmospheric conditions are provided by the WRF model, and high-resolution Navier-Stokes simulations are carried out using FLUENT. To ensure ground surface compatibility and resolve inconsistencies caused by variations in mesh-grid structures and resolutions between the models, modified boundary conditions and an unstructured grid framework were applied. Data from the WRF were integrated into FLUENT via User-Defined Functions (UDFs). This approach enhanced the accuracy of turbulent atmospheric flow solutions and improved adaptability to time-dependent variables.
As it known, one of the challenges in the meteorological modeling is representing maximum values, which are expected to observe frequently during climate change. In here, the analyses were conducted for Istanbul Airport, one of the busiest airports in the world, focusing on the dates with the maximum wind speed values. The combined model outputs were compared with observations from the meteorological station in the region, followed by a comprehensive analysis of the wind flow fields across the area. The results demonstrated that low-resolution meteorological models can be successfully integrated into high-resolution CFD simulations, leading to significant improvements in the spatial and temporal resolution of turbulent flow analyses. Moreover, this approach offers broad applicability in areas such as renewable energy and weather forecasting. The study presents a new methodology for atmospheric flow simulations by improving data compatibility and solution accuracy between models.
How to cite: Mut, A. O. and Şahin, A. D.: Coupled Mesoscale Weather Prediction and Computational Fluid Dynamics Modeling for Maximum Wind Flow Analysis: A Case Study for Istanbul Airport, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11687, https://doi.org/10.5194/egusphere-egu25-11687, 2025.
The Ozmidov scale marks the cutoff scale above which overturning fluid motions in stably stratified shear flows are energetically prohibited. A recent study of a turbulent shear layer demonstrates that the Corrsin scale provides an intrinsic cutoff scale when stratification is absent [1]. For the neutral boundary layer, it is proposed by analogy to the mixing layer that the cutoff scale is linked to the Corrsin scale rather than the unbounded Ozmidov scale. The claim is numerically investigated for turbulent Ekman flow with the aid of Kerstein’s one-dimensional turbulence (ODT) model [2], utilizing the case setup described in [3]. ODT offers full-scale resolution along a vertical coordinate by autonomously evolving the instantaneous property profiles. Molecular diffusion is directly resolved, whereas turbulent advection is modeled by a stochastic process that is formulated with the aid of spatial mapping events, which are sampled based on the local available energy. In this model formulation, a cutoff scale is economically prescribed by limiting the sampling range of turbulent scales. Model results in terms of low-order and detailed turbulence statistics will be presented and compared to available reference data and theoretical analysis.
References
[1] F. G. Jacobitz and K. Schneider. Phys. Rev. Fluids 9:044602, 2024.
[2] A. R. Kerstein and S. Wunsch. Bound.-Lay. Meteorol. 118:325–356, 2006.
[3] M. Klein and H. Schmidt. Adv. Sci. Res. 19:117–136, 2022.
How to cite: Klein, M. and Schmidt, H.: Investigating cutoff scales in turbulent Ekman flow with a map-based stochastic modeling approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13495, https://doi.org/10.5194/egusphere-egu25-13495, 2025.
Terrain-slope increases with and without upslope large surface roughness are found impacting downstream shear-generated turbulence differently in the nighttime stable boundary layer (SBL). Their different influences can be clearly identified in their different derivations in the relationship between turbulence and wind speed at a given height, known as the HOckey STick (HOST) transition, from the HOST relationship over a flat terrain. Due to transport of the cold surface air down from elevated uniform terrain in reducing the downstream air temperature not much stratification, the downstream hydrostatic imbalance increases with terrain slope resulting in enhanced turbulence for a given wind speed. The rate of turbulence increase with wind speed from this downslope flow, on the other hand, is independent of terrain slope. With turbulent mixing enhanced by upslope large surface roughness elements, the upslope cold surface air is elevated from the upslope terrain surface. Horizontal transport of this elevated cold turbulent air layer reduces the downstream upper warm air temperature, resulting in the increasing reduction of the downstream stable stratification with height. As the consequence of the effective wind-shear generation of turbulence with the reduced stratification, the downstream near-neutral turbulence increase with wind speed is enhanced with height in addition to the turbulence intensity enhancement from the cold downslope flow. The study demonstrates important physical mechanisms for turbulence generation captured by HOST and detection of terrain features for their impacts on those mechanisms through their deviations from the HOST relationship over a flat terrain.
This study demonstrates key physical mechanisms for turbulence generation captured by the HOST relationship. It also highlights the influence of terrain features on these mechanisms through deviations from the HOST relationship observed over flat terrain.
The study is supported by US National Science Foundation (NSF), AGS-2203248, AGS-2220664, and AGS-2231229 for JS; AGS-1733877 and AGS-2220663 for JW, SB, and DK; AGS-1733746, AGS-1843258, and AGS-2220662 as well as the University of South Carolina Department of Geography for AH; and AGS-1844426 for GP. SB was also partly supported by the NOAA cooperative agreement NA220AR4320151 for the Cooperative Institute for Earth System Research and Data Science (CIESRDS).
How to cite: Sun, J., Bhimireddy, S., Kristovich, D., Wang, J., Hiscox, A., Mahrt, L., and Petty, G.: Impacts of Terrain Slope and Surface Roughness Variations on Turbulence Generation in the Nighttime Stable Boundary Layer, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6841, https://doi.org/10.5194/egusphere-egu25-6841, 2025.
Nocturnal downvalley flows were examined in a valley located in southern France, near the Pyrenees. Three meteorological stations were strategically placed at different locations within the valley, collecting a year-long dataset of near-surface observations. This dataset enables an investigation of how these flows are organized and evolve throughout the annual cycle.
To identify the downvalley flow events, we applied a breeze detection algorithm (Arrillaga et al., 2018; Román-Cascón et al., 2019). Once detected, the events were characterized in terms of onset, peak intensity, and duration, with particular attention paid to the synoptic conditions conducive to their development. A clustering approach was also employed to classify and compare subtypes of breeze days, providing insights into their controlling factors and distinctive features.
Furthermore, a statistical analysis differentiating various turbulence regimes (incorporating HOckey STick (HOST) analysis) offers a deeper understanding of how turbulence interacts with flow dynamics. Overall, this work seeks to advance our knowledge of the mechanisms driving thermally-driven flows in complex terrain over a full annual cycle.
How to cite: Ortiz-Corral, P., Román-Cascón, C., Jiménez-Rincon, J. A., Lohou, F., Lothon, M., Sastre, M., Sun, J., and Yagüe, C.: Statistical Analysis of Nocturnal Downvalley Flows Over the Annual Cycle: Insights from a Pyrenean Valley (France), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16689, https://doi.org/10.5194/egusphere-egu25-16689, 2025.
Sea breezes are mesoscale phenomena formed in coastal regions when winds at the synoptic scale are weak. During the daytime, their general (and well-known) picture includes sea-to-land winds at the surface and land-to-sea ones at a certain height, closing the breeze circulation. However, this canonical picture is rarely observed from observations due to the interactions of the sea breezes with other flows, such as those related to the background (weak to moderate) synoptic conditions, the development of other local flows and/or the interactions with other processes within the atmospheric boundary layer, among others. This study shows an in-depth analysis of these interactions based on data gathered from surface stations and radiosoundings launched during different sea-breeze events detected in the northern zone of the Gulf of Cádiz (SW Spain). These winds have important impacts in this area during summer, especially due to their capacity to refresh warm temperatures and transport humidity.
This study has been developed within the LATMOS-i1, WINDABL2, and WIND4US3 projects, all of which include, among their objectives, the study of the interaction between coastal breezes and upper winds through different observational and modelling strategies. In this work, we present part of the observational strategy developed at the Gulf of Cádiz, which consisted of 1) the installation of meteorological and atmospheric turbulence stations at strategic locations for the long-term monitoring of breezes, as well as; 2) the launching of atmospheric radiosoundings during intensive observation periods characterised by sea-breeze conditions. We also present some results from the analysis of events with different characteristics, allowing us to highlight how they differ during contrasting background winds and under conditions with different thermodynamic vertical structures of the atmospheric boundary layer.
1 The LATMOS-i project (PID2020-115321RB-I00) (Land-ATMOSphere interactions in a changing environment: How do they impact on atmospheric-boundary-layer processes at the meso, sub-meso and local scales in mountainous and coastal areas?), funded by MCIN/AEI/ 10.13039/501100011033.
2 The WINDABL project (PR2022-055) (How are the Surface Thermally Driven Winds influenced by the vertical structure and horizontal inhomogeneities of the Atmospheric Boundary Layer?), funded by Plan Propio de la Universidad de Cádiz, Convocatoria 2022 de Proyectos para investigadores nóveles.
3The WIND4US project (CNS2023-144885) (Disentangling the complexity of the WIND systems in coastal areas FOR a better Understanding of their impacts on Society), funded by Convocatoria 2023 de Proyectos de Consolidación Investigadora.
How to cite: Román-Cascón, C., Ortiz-Corral, P., Luján-Amoraga, E., Jiménez-Rincón, A., Bolado-Penagos, M., Bruno, M., Izquierdo, A., Sun, J., and Yagüe, C.: Horizontal and vertical analysis of sea breezes in the Gulf of Cádiz (SW Spain) from surface stations and radiosounding data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15917, https://doi.org/10.5194/egusphere-egu25-15917, 2025.
Extreme weather events, such as heat waves, are increasingly common during summers in the
Mediterranean area. The effect of urban overheating -known as the increase of the average
temperature within the urban canopy caused by the heat storage on their surfaces thanks to their
optical and thermal characteristics, in addition to the heat emissions due to anthropogenic activities-
can cause the thermal stress of the population in the city to increase significantly during these
episodes, leading to serious health consequences. The study of this type of impact must be
quantified by means of thermal comfort indices that establish a relationship between the
meteorological conditions observed or predicted by a model and the physiological response of
human beings, such as the Universal Thermal Climate Index (UTCI). In this work, we study the
spatial-temporal behaviour of the UTCI in the city of Valencia (east coast of Spain) during a heat
wave (HW) and non-heat wave (NHW) period in August 2023 using the mesoscale meteorological
model (WRF, Weather Research and Forecasting) and in situ observations. For this purpose, a
comparison of atmospheric conditions in the planetary boundary layer (PBL) is performed, as well as
a study of the influence of temperature, shortwave and longwave radiation (from the mean radiant
temperature, TMR), wind speed and relative humidity on the behaviour of the UTCI. The main
results show a similar spatial distribution and temporal evolution of the UTCI for both periods,
differing in the magnitude of the UTCI. The positive (negative) temperature anomaly with regards to
the rest of the month is mainly the factor that causes a greater increase (decrease) in UTCI during
the HW (NHW). There is also a less developed PBL during the HW, as a consequence of the lower
intensity of the coastal breeze in the city during this period, which also has a significant effect on the
increase in UTCI during the HW.
How to cite: Sánchez-Lorente, Á., Martilli, A., Sánchez, B., and Yagüe, C.: Mesoscale modeling of the urban boundary layer in a coastal city. The case of Valencia., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4133, https://doi.org/10.5194/egusphere-egu25-4133, 2025.
Knowledge on both the mean field and fluctuations of concentration is necessary to estimate risks linked to pollutant exposure on industrial sites. While time-averaged concentrations provide meaningful information for chronic risk exposure, local exceedance of high concentration values potentially trigger chemical reactions or exceed harmful limits for living organisms. Information on threshold exceeding is thus a key parameter for toxicity assessment and accident management, hence the focus of this work on concentration fluctuations.
Several models for the probability distribution functions (PDF) of pollutant concentrations have been proposed in the literature. Several authors agree on the fact that the gamma distribution provides a reliable model for the one-point concentration PDF in case of localised releases of pollutants in atmospheric boundary layers (Cassiani et al., 2020). However, the accuracy of the gamma distribution was still not properly investigated within domain characterised by a complex geometry.
This is indeed the aim of this experimental study, focusing on the one-point concentration PDF due to a localised release of pollutant within a group of buildings. Furthermore, we aim at verifying models predicting average times of exceeding concentration thresholds (e.g. Bertagni et al., 2020).
Wind and concentration fields were characterised on the small-scale model of an idealised industrial site in a wind tunnel reproducing the atmospheric boundary layer. Higher order statistics were computed from concentration time series collected with a fast flame ionisation detector of frequency 400 Hz. In addition to the work presented hereby, this experimental dataset could be used to validate numerical dispersion models in future studies.
Best agreement between the experimental one-point concentration PDF and the gamma distribution are observed in the mid- and far-field. In contrast, the gamma distribution induces a systematic underestimation of concentration fluctuations in the near-field. Notably the Gamma distribution does not capture the occurrence of high intensity peaks measured sporadically, especially in recirculating regions in building wakes.
Mean threshold exceeding times are computed assuming a gamma distribution and hence show best correlation with experimental data in the mid- and far-field. Frequency of threshold exceeding show less accurate results for higher limits.
Summarising, the gamma distribution is shown to be a reliable model for the one-point concentration PDF in the mid- and far-field, but exhibits poor correlation in the near-field due to the presence of recirculation zones and intense meandering motion of the pollutant plume. The model for mean times of threshold exceeding, relying on the assumption of a gamma distribution, show a similar behaviour.
References
Bertagni, M. B., Marro, M., Salizzoni, P., & Camporeale, C. (2020). Level-crossing statistics of a passive scalar dispersed in a neutral boundary layer. Atmospheric Environment, 230, 117518. https://doi.org/10.1016/j.atmosenv.2020.117518
Cassiani, M., Bertagni, M. B., Marro, M., & Salizzoni, P. (2020). Concentration Fluctuations from Localized Atmospheric Releases. Boundary-Layer Meteorology, 177(2), Article 2. https://doi.org/10.1007/s10546-020-00547-4
How to cite: Schiavini, C., Marro, M., Salizzoni, P., Soulhac, L., Ravina, M., Panepinto, D., and Zanetti, M.: Concentration fluctuations and mean time of exceeding of hazard thresholds on industrial sites, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6010, https://doi.org/10.5194/egusphere-egu25-6010, 2025.
This study presents findings from the FATIMA-YS campaign, an international collaborative effort to investigate marine atmospheric processes over the Yellow Sea, conducted at the Socheongcho Ocean Research Station (S-ORS) from June 20 to July 9, 2023. The Yellow Sea is a critical region for studying marine atmospheric boundary layer (MABL) dynamics due to its unique air-sea interaction processes driven by seasonal variability and complex coastal influences.
During the campaign, radiosonde observations at S-ORS captured the formation and evolution of a stable boundary layer (SBL) on June 30 and July 1, under conditions of warm air masses overlying cooler sea surfaces, accompanied by weak horizontal winds. These observations revealed a sharp temperature inversion near the surface, indicative of strong atmospheric stability and limited vertical mixing.
Turbulent fluxes were measured using eddy covariance instruments, capturing unique characteristics of air-sea interactions under stable conditions. These observational findings will be presented alongside numerical model simulations to explore the dynamics of the MABL under stable conditions.
How to cite: Kim, H., Heo, K.-Y., Jeong, J.-Y., and Fernando, H. J.: Marine Atmospheric Boundary Layer Characteristics Observed during the FATIMA-YS Campaign at the S-ORS, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8050, https://doi.org/10.5194/egusphere-egu25-8050, 2025.
Nocturnal Low-Level Jets (NLLJ) are known to be a crucial process in the long-range transport of atmospheric pollutants with a positive or negative impact on air quality. In recent years, the study of NLLJ that occur usually at the top of the atmospheric boundary layer (ABL) has been greatly enhanced by recent technological and methodological advances in ground-based remote sensing instruments. They are now able to provide continuously high-quality profiles of ABL parameters that can be obtained from automatic LIDAR-ceilometers (ALC) providing information about clouds, precipitations, aerosols (including aerosol characteristics and types with depolarization measurements) and from wind Doppler LIDAR (WDL) providing information about wind profile characteristics.
At the Royal Meteorological Institute of Belgium (RMI), we have been developing a new pioneering algorithm (CONIOPOL: CONIOlogy + POLarization) based only on ALC measurements with a depolarization function (VAISALA CL61) to provide in real-time automatic identification of cloud phase, precipitation type and aerosol type. By combining the output of CONIOPOL based on measurements from a CL61 installed in Uccle (Brussels) with measurements from a WDL located at Brussels Airport (15km away from the CL61), it is possible to monitor continuously the transport of aerosols by NLLJ.
The synergy between both instruments will be illustrated by an interesting case study, showing the transport of marine aerosols by NLLJ into the ABL characterized in the presence of dust. The characteristic and the evolution of the synoptic situation will be used to highlight the geographical origin of aerosols. In order to better characterize the type identification of aerosols by CONIOPOL, ground measurements concerning the physical properties of aerosols carried out close to the CL61 will also be presented.
How to cite: Mangold, A., Laffineur, Q., Koistinen, E., and Delcloo, A.: Synergy between ground-based remote sensing instruments: a new approach to better understand the transport and dispersion process of aerosols in the atmospheric boundary layer, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10335, https://doi.org/10.5194/egusphere-egu25-10335, 2025.
We present our progress towards satellite-based monitoring of one or more key parameters of the well-mixed, planetary boundary layer (PBL). These may include the boundary layer height and the boundary layer moisture for clear-sky pixels. These influence the initiation and life cycle of convective clouds and storms. Remote sensing of these parameters could be beneficial to short-range forecasting, nowcasting and process studies.
In our work, we utilize observations in the near-infrared (NIR) at 0.9 µm and in the thermal-infrared (TIR) at 11 µm. In the NIR-region we exploit bands placed inside and shortly outside a water vapour (WV) absorption feature which allows us to sense the total column of WV (TCWV). In the TIR-region, we use the so-called split-window bands. Typically, these bands are positioned at 11 µm and 12.2 µm, respectively. The difference of the two channels is the split-window difference (SWD). The SWD is affected by the surface emissivity, the air temperature and the WV content in the layers above. For example, the new Flexible Combined Imager (FCI) on the geostationary satellite Meteosat Third Generation (MTG) carries these measurements, allowing the monitoring at 10 min temporal resolution and at 1 km spatial resolution.
In initial sensitivity studies, we explore the potential of the SWD for PBL remote sensing. The SWD can be linked to the thickness of the mixed layer, as well as the moisture contained in the mixed-layer. However, ambiguity exists in distinguishing between thickening and moistening processes within the PBL. Combining these observations, with their different sensitivities to WV distribution, may help resolve the ambiguity to some extent and provide more robust information on the moisture distribution in the PBL.
Our current efforts focus on investigating how to optimize the integration of these complementary measurements to enhance the retrieval of not only the TCWV but also additional information on the moisture structure in the lower levels of the atmosphere.
How to cite: El Kassar, J., Carbajal Henken, C., Preusker, R., and Fischer, J.: Retrieving Parameters of the Planetary Boundary Layer from Near- and Thermal-infrared Satellite Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16873, https://doi.org/10.5194/egusphere-egu25-16873, 2025.
Advances in computational power have enabled atmospheric simulations across a broad range of scales, including the coupling of mesoscale simulations to nested large-eddy simulations (LES), where the largest turbulent eddies in the atmospheric boundary layer are resolved. However, resolved turbulence does not instantaneously develop at the mesoscale-LES interface, necessitating turbulence generation methods to accelerate the transition from the smoother mesoscale inflow to resolved turbulence in the domain interior.
We evaluate two turbulence generation methods that both apply pseudo-random perturbations at the lateral inflow boundaries. These methods are the cell perturbation method (CPM), which introduces potential temperature perturbations, and the force CPM (FCPM), which applies vertical force perturbations at the lateral boundaries. Building on the previous suggestion for the FCPM, we derive an optimized scaling law for the perturbation amplitude in this turbulence generation method. The scaling law accounts for simulation setup and inflow characteristics, including wind speed, wind direction, and static stability, and is validated using LES of idealized boundary layers.
Additionally, we perform real-case atmospheric LES that reveal significant limitations of the CPM, such as spurious precipitation under specific atmospheric conditions. In contrast, the FCPM, particularly with our proposed extensions, demonstrates robust performance, producing minimal artefacts while effectively accelerating turbulence generation, making it the preferred method for turbulence generation.
We further discuss pathways to generalize the FCPM for larger domains and longer simulations, addressing challenges such as spatially and temporally varying boundary layer characteristics. These advancements represent a step towards a flow- and scale-aware turbulence generation method, facilitating efficient coupling between mesoscale simulations and LES.
How to cite: Krieger, N. and Kühnlein, C.: Extending turbulence generation methods for efficient mesoscale-to-LES coupling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15291, https://doi.org/10.5194/egusphere-egu25-15291, 2025.
Large Eddy Simulations are widely used to study the Atmospheric Boundary Layer, since they resolve sufficient turbulence features to capture realistic boundary layer dynamics. For this purpose, the surface roughness of the terrain is often implemented by a roughness parameter that increases turbulence production near the surface through the stress tensor of the subgrid-scale model, in accordance with Monin-Obukhov theory. In Implicit Large Eddy Simulations, the absence of a subgrid-scale model simplifies implementation and reduces potential error sources at faster computational speeds, but does not permit the aforementioned implementation of the surface roughness. A drag coefficient can be used to integrate the effects of the surface roughness in Implicit Large Eddy Simulations. However, we propose a novel approach that models the surface roughness through a stochastic height variation of the lowest simulation layer. The method captures the impact of small-scale surface heterogeneity more effectively than a traditional uniform roughness parameter or drag coefficient model, while still just being controlled by a single parameter that prescribes the amplitude of the height variation. We find that this parameter has a linear correlation to the measured surface roughness in the corresponding simulation, with high numeric stability even for high wind speeds.
How to cite: Wahl, E., Yazbeck, T., and Schlutow, M.: Implicit Large Eddy Simulations of Boundary Layer Flows: Modeling Surface Roughness by Stochastic Microtopography, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11186, https://doi.org/10.5194/egusphere-egu25-11186, 2025.
Large-eddy simulations (LESs) are known to significantly overestimate entrainment in cloud-topped boundary layers, negatively impacting predictions on cloud mass and cover. This overestimation stems from coarse model resolutions that lead to numerical broadening of the entrainment layer. While it has been shown in direct numerical simulations (DNSs) that down-to-centimetre-scale resolutions can mitigate this issue, such high resolutions are not viable for most applications in the atmospheric sciences. The one-dimensional turbulence model (ODT), introduced by Kerstein [1], offers a computationally efficient alternative that provides full-scale resolution along a 1-D vertical domain. Molecular diffusion is explicitly resolved, while turbulent advection is modelled through a stochastically sampled sequence of spatial mappings, known as eddy events. Physically plausible eddy events are selected based on their current kinetic and potential energy. This allows an accurate representation of local turbulence properties and their dynamical complexity by evolving instantaneous property profiles. This study applies ODT to investigate cloud-top turbulent mixing processes driven by radiative cooling in a smoke cloud, benchmarking the results against DNS. Building on the preliminary findings by Meiselbach [2], we demonstrate improvements in mean profiles and turbulent fluxes of buoyancy and smoke concentration, showing ODT's ability to reproduce salient features observed in DNSs. In addition, we explore convective boundary layer scalings at extended Reynolds and Richardson numbers beyond those accessible in DNS studies.
References:
[1] A. R. Kerstein, Journal of Fluid Mechanics 392, 277334 (1999).
[2] F. T. Meiselbach, Application of ODT to Turbulent Flow Problems, doctoral thesis, BTU Cottbus-Senftenberg (2015).
How to cite: Li, H., Klein, M., and Schmidt, H.: Simulation of radiatively driven mixing in a smoke cloud using "one-dimensional turbulence", EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9491, https://doi.org/10.5194/egusphere-egu25-9491, 2025.
Realistically representing the vertical turbulent transport of surface layer fluxes dealt with by the planetary boundary layer (PBL) scheme is of paramount importance in a numerical weather forecasting model. Further complexity arises due to the presence of heterogeneous surface obstacles whose height can be comparable to the model's vertical resolution, which poses a challenge in improving and revisiting the PBL scheme. In this presentation, we derive the numerical method to couple one of the recently validated turbulent kinetic energy (TKE)-based non-local PBL schemes, namely the TKE-ACM2 scheme, with the commonly used multi-layer Building Effect Parameterization (BEP) model in WRF. The behavior of TKE-ACM2+BEP is first examined under idealized convective atmospheric conditions where a simplified staggered urban morphology is prescribed. Its performance is benchmarked against the state-of-the-art large-eddy simulation by PALM and also compared with the operational PBL scheme Boulac+BEP. The idealized simulation results reveal that TKE-ACM2+BEP exhibits superiority in simulating the potential temperature and wind speed profiles compared to Boulac+BEP, corroborating its better non-local treatment of the momentum fluxes near the roughness sublayer. Furthermore, we apply the coupled model to the Pearl River Delta region in South China, where a few extensively urbanized mega-cities exist. The one-month high-resolution wind speed LiDAR observations indicate that TKE-ACM2+BEP provides a more reasonable reproduction of wind speed profiles in the upper surface layer compared to the Bulk methods (i.e., without urban canopy model) by reducing the overestimation at the urban LiDAR site. In addition, the 10-m wind speeds (U10) are compared with surface stations aggregated based on the Local Climate Zone classification. The results suggest that the BEP model can improve the performance of the TKE-ACM2 PBL scheme at low- to moderate-building grids, but may not be consistently better at high-building density grids as it overly reduces U10.
How to cite: Zhang, W., Wong, M. M. F., and Fung, J. C. H.: Improving the Urban Boundary Layer Wind Speed by Coupling the TKE-ACM2 PBL Scheme with the Building Effect Parameterization Model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2133, https://doi.org/10.5194/egusphere-egu25-2133, 2025.
The interaction between sea ice and atmosphere depends strongly on the exchange of momentum and heat in the Arctic boundary layer (BL). The representation of the Arctic BL is still a major source of uncertainty in recent climate models since they struggle to accurately model turbulent exchange in the predominantly stable-stratified BL of the Arctic. An additional source of uncertainty is the representation of sea-ice roughness in climate models. Sea-ice roughness is an important factor determining the mechanical production of turbulence. Here, we study the performance of the BL scheme of the numerical weather prediction model ICON-NWP and investigate the sensitivity to different values of sea-ice roughness. Therefore, we set-up ICON limited area simulations forced by ERA5 that include the track of the MOSAiC campaign in 2019-2020 and apply different values for the sea-ice roughness. ICON takes a constant roughness value for sea ice (default: 0.001 m) within a sea-ice tile whenever the ice thickness reaches a critical value. The results are compared to turbulence measurements during MOSAiC and we further investigate regional effects that occur in relation to the changed roughness values.
How to cite: Gebhardt, F. and Handorf, D.: Simulations of Arctic winter stable-boundary layers during MOSAiC campaign using ICON-NWP and the influence of sea-ice roughness, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17533, https://doi.org/10.5194/egusphere-egu25-17533, 2025.
