The Planetary Boundary Layer (PBL), which influences the dispersion of air pollution and the exchange of heat, water vapour and chemical species between the atmosphere and the surface, plays a very important role in air quality, weather and climate. The diurnal evolution of the PBL is driven by incoming solar radiation, which controls surface fluxes and vertical thermal dynamics. Thus, radiatively important atmospheric chemical species, such as anthropogenic or natural aerosols, which are primarily emitted or secondarily formed from precursors emitted from the surface and further diluted within the PBL, should have strong interactions with the PBL meteorology. This presentation will provide observational and modelling evidence on the interactions between atmospheric chemistry and the atmospheric boundary layer and their impacts on air quality in megacities (Ding et al., 2016) and transboundary air pollution transport between city clusters in the gigacity region of eastern China (Huang et al., 2020), and will present some recent results and insights from intensive field campaigns of chemical and physical parameters and their vertical profiles in eastern China based on a super-tethered airship platform. This presentation will also explore the impact of these interactions on wildfire/agricultural straw burning extreme events in different climate regimes, such as eastern China and the Indo-China peninsula in monsoon Asia, and the west coast of the United States with Mediterranean climate (Ding et al., 2013; Ding et al., 2021; Huang et al., 2023), and discuss the potential implications for chemical weather prediction and climate studies (Huang and Ding, 2021).

References

Ding, A. et al., Intense atmospheric pollution modifies weather: a case of mixed biomass burning with fossil fuel combustion pollution in eastern China, Chem. Phys., 13, 10545-10554, 2013.

Ding, A. et al., Enhanced haze pollution by black carbon in megacities in China, Res. Lett., 43, 2873-2879, 2016.

Ding, K. et al., Aerosol-boundary-layer-monsoon interactions amplify semi-direct effect of biomass smoke on low cloud formation in Southeast Asia, Nature Commun. 12, 6416, 2021.

Huang, X., Ding, Aerosol as a critical factor causing forecast biases of air temperature in global numerical weather prediction models, Science Bulletin, 66(18), 1917-1924, 2021.

Huang, X. et al., Amplified transboundary transport of haze by aerosol–boundary layer interaction in China, Nature Geoscience, 13, 428-434, 2020.

Huang, X. et al., Smoke-weather interaction affects extreme wildfires in diverse coastal regions, Science, 379, 457-461, 2023.

How to cite: Ding, A.: Interactions of Atmospheric Chemistry and Atmospheric Boundary Layer: From Megacity to Gigacity, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-473, https://doi.org/10.5194/ems2024-473, 2024.

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The higher-order turbulence scheme, Cloud Layers Unified by Binormals (CLUBB), is known for effectively  simulating the transition from cumulus to stratocumulus clouds within leading atmospheric climate models.  Here we investigate an underexplored aspect of CLUBB: its capacity to simulate near-surface winds and the Planetary Boundary Layer (PBL), with a particular focus on its coupling with surface momentum flux, modelling of turbulent lengthscale, and direct prognosis of turbulent momentum flux. First, using the GFDL atmospheric climate model (AM4), we examine two distinct coupling strategies, distinguished by their handling of surface momentum flux during the CLUBB’s stability-driven substepping performed at each atmospheric time step.  The static coupling maintains a constant surface momentum flux, while the dynamic coupling adjusts the surface momentum flux at each CLUBB substep based on the CLUBB-computed zonal and meridional wind speed tendencies. Our 30-year present-day climate simulations (1980-2010) show that static coupling overestimates 10-m wind speeds compared to both control AM4 simulations and reanalysis, particularly over the Southern Ocean (SO) and other midlatitude ocean regions. Conversely, dynamic coupling corrects the static coupling 10-m winds biases in the midlatitude regions, resulting in CLUBB simulations achieving there an excellent agreement with AM4 simulations. Furthermore, analysis of PBL vertical profiles over the SO reveals that dynamic coupling reduces downward momentum transport, consistent with the found wind-speed reductions. Instead, near the tropics, dynamic coupling results in minimal changes in near-surface wind speeds and associated turbulent momentum transport structure. Then, implementing a more generalized calculation of the turbulent length scale leads to an overall degradation of winds but improves root mean square error and bias of low cloud amount in key regions of stratocumulus to cumulus transition. Remarkably, we show that updating CLUBB formulation of momentum flux from diagnostic to prognostic, to permit countergradient momentum fluxes, improves nearly everywhere global winds, while retaining the benefits of the more generalised lengthscale formulation in accurately capturing the low cloud amount. Finally, the wind turning angle serves as a valuable qualitative metric for assessing the impact of changes in surface momentum flux representation on global circulation patterns.

How to cite: Gentile, E. S., Zhao, M., Larson, V., and Zarzycki, C.: Enhancing global wind climate simulations in the GFDL-AM4 model by unifying planetary boundary layer and cloud turbulence parametrizations with the higher-order scheme CLUBB, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-207, https://doi.org/10.5194/ems2024-207, 2024.

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The Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment (LIAISE) campaign examined the impact of anthropization on the water cycle in terms of land-atmosphere-hydrology interactions. The objective of this study is to assess the effects of irrigation on the atmosphere and on precipitation in WRF model simulations during the LIAISE Special Observation Period in July 2021 (LIAISE-2021 SOP). Comparisons between simulations and observations show better verification scores for air temperature, humidity and wind speed and direction when the model included the irrigation parameterization, improving the model warm and dry bias at 2 m over irrigated areas. Other changes found are the weakening of the sea breeze circulation and a more realistic surface energy partitioning representation, where the latent heat flux is prevailing over the sensible heat flux. The boundary layer height is lowered in the vicinity of irrigated areas, causing a decrease in the lifting condensation level and the level of free convection, which induce increases in convective available potential energy (CAPE) and convective inhibition (CIN).

Precipitation differences between simulations become relevant for smaller areas, close to the irrigated land. When convection is parameterized, simulations including irrigation tend to produce a decrease in rainfall (negative feedback) while convection-permitting simulations produce an increase (positive feedback), although the latter underestimates substantially the observed precipitation field. In addition, irrigation activation decreases the areas exceeding moderate hourly precipitation intensities in all simulations. There is a local impact of irrigated land on model-resolved precipitation accumulations and intensities, although including the irrigation parameterization did not improve the representation of the observed precipitation field, as probably the precipitation systems during LIAISE-2021 SOP were mostly driven by larger scale perturbations or mesoscale systems, more than by local processes. Results reported here not only contribute to enhance our understanding of irrigation effects upon precipitation but also demonstrate the need to include irrigation parameterizations in numerical forecasts to overcome the biases found.

This research has been funded by projects WISE-PreP (RTI2018-098693-B-C32), ARTEMIS (PID2021-124253OB-I00) and the Institute for Water Research (IdRA) of the University of Barcelona.

How to cite: Udina, M., Peinó, E., Polls, F., Mercader, J., Guerrero, I., Valmassoi, A., Paci, A., and Bech, J.: Irrigation impact on boundary layer and precipitation in WRF model simulations (LIAISE-2021), EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-78, https://doi.org/10.5194/ems2024-78, 2024.

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In the bulk of the convective boundary layer driven by surface heating, the vertical-velocity variance is known to scale with the convective velocity scale. This scaling relies on the quasi-equilibrium assumption that the surface heat flux (H) varies slowly compared to the adjustment time scale of the large scale convective eddies (or the eddy-turnover time scale). When the surface heat flux decays moderately or rapidly compared to the eddy-turnover time scale, a departure from the quasi-equilibrium regime is expected. A recent study proposed a parameter for describing such departure during the late afternoon transition: r = H^-1dH/dt^-1/t_*, where t_* is the eddy-turnover time scale. The quasi-equilibrium assumption applies when r>>1, and breaks down when r~1. Building on these results, we further investigate the scaling for the vertical-velocity variance in the regime r<<1 where the surface heat flux decays rapidly compared to the eddy-turnover time scale. In a first step, we use large-eddy simulations to reveal that the regime r<<1 is characterized by a new velocity scale w_*r = (g/θ dH/dt z_i²)^1/4depending on the actual dH/dt rather than H . We argue that the characteristics of the surface heat flux during the initial-state quasi-equilibrium regime are encoded in the actual boundary-layer depth during the following out-of-equilibrium regime. In a second step, we demonstrate that the new velocity scale can be deduced from scaling arguments applied to the budget-equation of the vertical turbulent heat flux. The new velocity scale aims to specifically describe the vertical-velocity variance during the latest decay-stage of the positive surface heat flux, that is a few minutes only before it turns negative. Further research is needed to understand which part of our results can be generalized to other non-stationary configurations, and challenge the results of this idealized study with observations.

How to cite: Elguernaoui, O., Li, D., and Reuder, J.: Scaling the vertical-velocity variance in the convective boundary layer forced by rapidly decaying surface heat flux after equilibrium breakdown, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-371, https://doi.org/10.5194/ems2024-371, 2024.

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The land surface, through its topography, soil moisture, temperature or vegetation activity, impacts the atmosphere from daily to seasonal time scale. An accurate assessment of the Land-Atmosphere (L-A) exchanges, and their correct representation, are therefore essential for weather and climate forecasts. However, Earth System Models (ESM) and Numerical Weather Prediction (NWP) often have large biases in their representation of surface-atmosphere flux when compared to observations. The detailed quantification and reduction of these biases are still on-going efforts in many modelling centres. The Models and Observations for Surface-Atmosphere Interactions (MOSAI) project aims at contributing to this effort, with a focus on the impact of surface heterogeneity.

The first step to achieve this objective is to conduct a fair and correct evaluation of the L-A interactions simulated by ESM and NWP. This is based on (i) reliable references against which the simulated L-A exchanges can be evaluated, and, (ii) relevant comparison methods able to point out the ESM and NWP weaknesses. These points define the two first scientific objectives of MOSAI project: (1) to investigate and determine the uncertainty and representativeness of L-A exchanges measured over heterogeneous landscapes. The second scientific objective (2) is to propose and test new methods to evaluate the L-A exchanges in ESM using long-term measurements.

The second step of the project concerns the improvement of the L-A exchanges simulated by the ESM and NWP. The coupling between land surface models (LSM) and atmospheric models is based on several simplifications which are different when considering Large Eddy Simulation (LES), weather or climate models. The third scientific objective (3) addresses some of these underlying simplifications in the coupling between LSM and atmospheric models, and their impacts on the simulated L-A exchanges.

From an observational prospective, MOSAI is based on long-term reference surface observations of research infrastructures (ACTRIS and ICOS) and on Enhanced Observing Periods (2021-2023) on three different ACTRIS-Fr sites. From the modelling prospectives, several ESM, NWP and LES models are involved.

In this presentation, we will state the objectives and strategy of MOSAI, and illustrate them with ongoing fields, works and results. The latter will notably address (1) the representativity of reference long-term measurements in a heterogeneous landscape, (2) the use of Neural Networks for the evaluation of models, (3) the impact of the heterogeneity on the boundary layer structure.

How to cite: Lohou, F. and the MOSAI field campaign team: Measured and simulated turbulent flux over heterogeneous surface: MOSAI project (Model and Observation for Surface Atmosphere Interactions), EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-589, https://doi.org/10.5194/ems2024-589, 2024.

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Accurate estimations of the surface temperature and momentum profiles are crucial to determine the exchange of energy and moisture between the surface and the atmosphere. Yet, getting a good estimate of the temperature profile over the widespread and frequently studied grass surface remains challenging. In this study, we present an extension to the Monin--Obukov similarity theory (MOST) for the roughness sublayer (RSL) over short vegetation. We test our theory using temperature measurements from fiber optic cables in an array-shaped set-up. This provides a high vertical measurement resolution that enables us to measure the sharp temperature gradients near the surface.

It is well-known that MOST is invalid in the RSL as the flow is distorted by roughness elements. However, to derive the surface temperature, it is common practice to extrapolate the logarithmic profiles down to the surface through the RSL. Instead of logarithmic behaviour defined by MOST near the surface, our observations show near-linear temperature profiles. This log-to-linear transition is described over an aerodynamically smooth surface by the Van Driest equation in classical turbulence literature. Here we propose that the Van Driest equation can also be used to describe this transition over a rough surface, by replacing the viscous length scale with a surface length scale L_s that represents the size of the smallest eddies near the grass structures. We show that L_s scales with the geometry of the vegetation and that the model shows the potential to be scaled up to tall canopies. The adapted Van Driest model outperforms the roughness length concept in describing the temperature profiles near the surface and predicting the surface temperature.

How to cite: Boekee, J., van der Linden, S., ten Veldhuis, M.-C., Verouden, I., Nollen, P., Dai, Y., Jongen, H., and van de Wiel, B.: Improved description of temperature profiles over short vegetation: rethinking the roughness height, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-127, https://doi.org/10.5194/ems2024-127, 2024.

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The usage of roughness length concept in atmosphere-vegetation modeling is convenient due to its simplicity. However, where the roughness length concept often leads to reasonable results, its empirical nature comes also at the cost of biases and parameter uncertainty as parameters become situation-dependent. For tall canopies, therefore, successful attempts have been made to explicitly model atmosphere-vegetation interaction as to avoid roughness length concepts and replace them by more physical parameterizations. For small canopies, such as grass, studies with that philosophy are very few. Yet, similar problems with roughness length concepts exist. Progress was hampered by our inability to probe the microclimate of grass due to its limited vertical extent. But with the appearance of miniaturized sensors, more and more observations of this thin,  intriguing layer have become available. Inspired by this, we aim to numerically simulate grass-atmosphere interaction with respect to momentum and heat and moisture exchange. We use direct numerical simulation (DNS) to explicitly simulate flow-obstacle interactions. Flow over rigid and non-rigid (flexible) grass elements are studied for different idealized configurations. We combine those 3D simulations with simplified 1D surrogates and analytical solutions (parameterizations) with the aim to replace the roughness length concept for grass with simple alternatives. It is shown that indeed such alternatives are possible and that, apart from the Reynolds numbers, there are strong physical parallels between flow over grass and flow of tall canopies. By exploiting those similarities, we think that biases due to usage of roughness length concepts can be avoided in the future.

How to cite: Van de Wiel, B., Yi, D., Boekee, J., Ten Veldhuis, M.-C., Sauerbier, J., Vis, G., ter Horst, T., and van der Linden, S.: Amazing grass: a numerical study of atmosphere-grass interactions, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-345, https://doi.org/10.5194/ems2024-345, 2024.

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Many studies have shown that the standard flux-gradient relations based on the similarity theory (MOST) are not fully applicable close to a surface covered with high roughness elements, due to the canopy-induced turbulent mixing caused by their interaction with the atmospheric flow. The effects of the so called roughness sublayer (RSL) on the surface-atmosphere coupling became more important since the lowest atmospheric level in NWP systems has been placed closer to the (vegetation or urban) canopies acting as roughness elements, entering the RSL. This in turn affects the effective surface fluxes of momentum, energy and gasses between the canopy and the atmosphere.

Different corrections to the traditional MOST attempting to account for the RSL effects on the surface layer theory are available. In this work we integrate Harman and Finnigan’s RSL theory (HF2008) into SURFEX8.1, a land surface model which is extensively used both offline and coupled to different NWP atmospheric models. HF2008 stands out as the most advanced theory of the RSL. It has been tested over forests and urban areas and implemented in land surface and NWP models, adding increased physical details in the classical similarity theory over a vegetated surface, and thus improving the surface-atmosphere coupling in NWP systems above tall vegetation. 

Our implementation is tested both through offline SURFEX experiments and online simulations in the Harmonie-Arome operational NWP system, and validated against observations in forest stations from the ICOS network. We address the differences in performance of the parameterisation, caused mainly by assumptions and simplifications usually done in the vegetation-atmosphere coupling in NWP systems.

How to cite: Viana, S. and Shapkalijevski, M.: The challenges of vegetation - atmosphere coupling in the roughness sublayer of a numerical weather prediction system, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-1015, https://doi.org/10.5194/ems2024-1015, 2024.

EMS2024-1015

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Over tall canopies such as forests the atmospheric surface layer is subdivided into an inertial sublayer (ISL) and a roughness sublayer (RSL). Inside the RSL the classic aerodynamic gradient method using Monin-Obukhov similarity theory (MOST) by itself does not represent the gradient well and is insufficient to calculate fluxes. Over the past decades multiple studies have proposed methods to extend MOST to account for the different turbulent conditions, containing a wide range of approaches and complexity. In this study we investigate how much complexity is necessary to calculate the flux more accurate and what we can learn from the respective complexity. A large dataset is required to assess the statistical robustness of the respective complexity during different environmental conditions. To this end, we study and apply the effect of forest roughness and directional heterogeneity in our flux calculations on a two-year dataset (2009-2010) of the sensible heat flux measured over a Douglas fir forest in the Netherlands. We apply standard MOST, an observational based method (the α-factor) and a physically based method (Harman and Finnigan, 2007, 2008) (hereafter HF07/08) together with a range of methods for the displacement height (d). Our results show that both a simple method (the α-factor) and a complex method (HF07/08) are able to more accurately represent the flux but that, as expected, standard MOST (regardless of the method estimating d) alone is insufficient. Both the α-factor and (HF07/08) allow to analyze large scale patterns in canopy turbulence. Differences between the methods lie in the level of detail and practical usability.

How to cite: Melman, E., Rutledge-Jonker, S., Braam, M., Frumau, A., Moene, A., Shapkalijevski, M., Vilà-Guerau de Arellano, J., and van Zanten, M.: Increasing complexity in Aerodynamic Gradient flux calculations inside the roughness sublayer applied on a two-year dataset, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-300, https://doi.org/10.5194/ems2024-300, 2024.

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This paper presents observations collected during the SOFOG3D campaign in South Western France during 2019-2020 to elucidate the processes involved in the deposition of fog droplets to the surface, a process that is often modelled in numerical weather prediction models, and forms an important component of the water budget within fog. The study suggests three main mechanisms cause deposition: turbulent, whereby water drops are transported to the surface in turbulent eddies; aerodynamic, whereby the mean horizontal wind deposits droplets directly onto surface canopy elements that protrude into the airflow, and gravitational, whereby droplets fall under the action of gravity directly onto the canopy. Results indicate that the gravitational settling is on average a minor component of the deposition, amounting to around 14% of the total figure. The study also identified that this proportion is relatively larger at 22%, when the turbulence intensity levels are low (vertical velocity variance < 0.003 m²s²). Consequently, for greater values of turbulence intensity the proportion is smaller at 11%. All three deposition processes are studied further using a multiple linear regression of terms against observed water deposition rates, in an attempt to evaluate various methods to estimate the deposition. Results indicate that a simple regression of liquid water content against observed deposition has some predictive skill, but that a multiple regression including all three terms produces better results with smaller regression errors. A simpler multiple regression, that merged turbulent and aerodynamic terms into a single ‘dynamic’ term produced results almost identical to the three-term multiple regression. Consequences for parametrization of liquid water deposition in fog are discussed.

How to cite: Price, J.: Observations and quantification of fog droplet settling made during the SOFOG3D campaign, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-369, https://doi.org/10.5194/ems2024-369, 2024.

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Shallow convection affects the shape of the Planetary Boundary Layer (PBL) and has a significant impact on low cloud formation, and thus on model computed mean tendencies and radiation budget. Recently, observational studies have been used to compare AROME (the kilometer-scale operational Numerical Weather Prediction model used at Météo-France) versus in situ observations of the radiation budget components. Comparisons with several measurement sites (Meteopole Flux, Sirta) have shown biases of solar radiations in AROME. Extended investigations have attributed a part of these biases to shallow convection scheme representing the PBL with rather poor performance, in particular stratocumulus clouds. The present work aims to investigate and improve the parameterizations used in AROME and Meso-NH models (both models share the same 1D physics package). Inconsistencies and bugs have been corrected, while new parameterization components and updates of the Eddy Diffusivity Mass Flux scheme (EDMF) have been added from the literature. This includes changes in the shallow convection, turbulence, subgrid cloud and microphysics schemes, from the updraft hypothesis to shallow cumulus subgrid precipitation. We use the Single Column Model (SCM) version of AROME (MUSC) to evaluate the adjustments brought to the model on well-known idealized cases of cloud development like cumulus over land (ARMCu) or ocean (RICO), stratocumulus (FIRE), transition cases (SANDU) and dry convection (IHOP, AYOTTE) as well. The Meso-NH research model is used to perform Large Eddy Simulations (LES), in which conditional sampling methods and diagnostics are applied to retrieve resolved quantities that serve as a reference for evaluating parameterizations. In addition, the semi-automatic tool High-Tune Explorer helps us to explore the n-dimensional space of free parameters of the parameterizations, and thus closes the EDMF scheme and then gives us hints on the sensibility over the set of relevant parameters. This complete update of AROME has shown significant improvements especially for stratocumulus cases, triggered precipitation and cloud formation on most of the cases.

How to cite: Marcel, A., Riette, S., Ricard, D., and Lac, C.: Improvements of shallow cloud and boundary layer parameterizations in the AROME-France model., EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-124, https://doi.org/10.5194/ems2024-124, 2024.

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Stratocumulus clouds are important for the Earth's planetary albedo and play a central role in determining Earth's sensitivity to forcing. Recent global-coupled simulations at kilometer-scale resolution in the atmosphere and the ocean, conducted in the framework of the H2020 nextGEMS project, offer opportunities to study cloud processes, their environmental factors, and the possibility of using observations to verify them. We investigate the representation of stratocumulus clouds by the ICON and IFS models and it allows us to compare both model strategies. The former uses less parameterizations to better understand process interactions and the latter considers shallow and deep convection schemes and more sophisticated parameterizations, which allows for better tuning. The results of this study show the value of both. The four-year simulations were assessed in terms of the top-of-atmosphere (TOA) albedo and the vertical structure of the atmospheric boundary layer in the coastal and offshore regions of Namibia, Peru and California. We used satellite data from the CERES-EBAF TOA dataset as an observational reference for the albedo. Both simulations reproduced the mean horizontal distribution and seasonal cycle of TOA albedo and the typical vertical structure of the low atmosphere. However, we found some discrepancies. IFS represented the stratocumulus regions slightly displaced towards the southwest, and lower albedo over the coastal regions in comparison with CERES. ICON represented too much cloud liquid water and uses a cloud inhomogeneity factor to reduce the albedo. Analysing the modeled cloud variability in space and time we found that ICON correctly reproduced the observed diurnal variation and the decrease in cloud depth towards the coast. However, the model simulated a more cellular than stratiform character of the cloud field, compared with satellite images.

How to cite: D'Amato Dragaud, I., Nowak, J., Dziekan, P., Lee, J., Mellado, J. P., and Stevens, B.: Stratocumulus variability in global storm-resolving models, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-909, https://doi.org/10.5194/ems2024-909, 2024.

EMS2024-909

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Clouds are such manifestations of turbulent flow in the atmosphere, where different physical processes and effects such as radiation, entrainment, microphysical interactions, non-zero gradients of vertical profiles of temperature and wind speed influence the flow at different scales. When analysing turbulence characteristics in clouds, one often assumes homogeneity, isotropy, and equilibrium. For such complicated systems as clouds, in which many thermodynamical and microphysical processes take place, these assumptions might fall short. If the turbulence characteristics are calculated along short windows, which still capture bigger scales of the order of the size of the cloud, then deviations from isotropy are observed in cloudy regions of the flight leg.

In this work, anisotropy is studied using anisotropy invariant maps. An example of anisotropy invariant map is the Lumley's triangle, which is a type of plot where theoretically possible values of invariants of anisotropic stress tensor are contained in a triangle figure. By studying the values of the invariants, one may connect the results to ideal geometrical cases such as elongation or contraction along one of the dimensions. Studying the time dependence of the values of the invariants gives an insight into different regimes of anisotropy in clouds.

The data under consideration comes from the EUREC4A campaign, where Twin-Otter aircraft performed penetrations of marine cumulus clouds near Barbados in 2020. Conditional statistics are made using the RQA method to differentiate between the cloud and its dynamical surroundings. By employing that differentiation, the extent of the anisotropy is studied. The effect of the averaging window is also considered. The preliminary results suggest that the turbulence in clouds is anisotropic to a degree.

How to cite: Krol, S., Wacławczyk, M., Jędrejko, P., and Malinowski, S.: Anisotropic turbulence in marine cumulus clouds, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-818, https://doi.org/10.5194/ems2024-818, 2024.

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Turbulent characteristics of the atmospheric surface layer are considered to be well understood over flat and horizontally homogeneous terrain. There, their initial description was provided by the Monin and Obukhov Similarity Theory (MOST; 1954) and fine-tuned using data from targeted observational campaigns (e.g., Businger et al., 1971). Since then, MOST has served as the basis for parameterization of turbulent exchange in numerical models and for processing of near-surface weather observations. Over complex heterogeneous terrain, however, classical MOST is not applicable due to violation of its underlying assumptions, and has been shown not to work. The recent work of Stiperski and Calaf (2023) has offered a way forward for turbulence parametrizations over non-ideal terrain, and has shown that MOST can be improved if the degree of turbulence anisotropy of the Reynolds stress tensor is included as an additional nondimensional parameter. From practical point of view, this raises a demand to parameterize the turbulence anisotropy over complex terrain for a possibly wide range of boundary-layer conditions.

The current study uses large eddy simulation technique to explore the impact of infinite sinusoidal topography on turbulence anisotropy in neutral and unstably stratified flows. The parameter range explored covers a range of hill heights and length scales, as well as geostrophic winds speeds, while the simulations are initialized with a constant surface heat flux. Simulations are carried out using the pseudo-spectral NCAR model with terrain-following coordinates (Sullivan et al., 2014).  The hill height is kept low due to the incompressible nature of the flow. As the model utilizes the MOST itself at the lower boundary, the simulations require very high-resolution to resolve a wide fraction of the inertial-range. Moreover, turbulence statistics are explored at a distance from the surface.

How to cite: Wójcik, D. and Stiperski, I.: Turbulence anisotropy in unstable stratified flows over hills: an idealized large eddy simulation study, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-450, https://doi.org/10.5194/ems2024-450, 2024.

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The exchange of momentum, heat and mass in the atmospheric boundary layer is primarily governed by thermally and dynamically driven processes that occur on a wide range of scales. This can lead to challenges in accurately describing these processes in Numerical Weather Prediction (NWP) models, especially in mountainous regions. With the ability to use finer grid spacings, more processes can be partially resolved. As a result, some of the commonly used parametrisations are no longer appropriate and need to be adjusted or even deactivated.

The ICOsahedral Non-hydrostatic model is used in Limited Area Mode (ICON-LAM) with the aim of providing a skillful forecast of the Alpine area at 500 m in the framework of GLORI (GLObal to Regional ICON digital twin). The model performs simulations in two-way nesting mode with the operational ICON-D2, including a nest with a horizontal grid spacing of 1 km. This domain covers the entire Alpine region and its horizontal resolution lies within the so-called “grey zone”, where turbulence, drag and convection are neither fully resolved by large-scale processes nor can they be modelled as a small-scale, sub-grid process.

Deterministic experiments are performed for the month of May 2022, as strong convective events have been observed in the Alps during this period. The simulation results are compared with various meteorological stations located at different altitudes within the complex terrain to study the effect of increasing the horizontal resolution and the performance of the model physics on the boundary layer. Small modifications in the grey zone related parametrisations, such as e.g. the turbulent kinetic energy scheme, show that the bias of near-surface variables like temperature and wind speed can be reduced. However, a more sophisticated approach is required for the higher resolution model to represent the complex interactions in the boundary layer.

How to cite: Littmann, D., de Lozar, A., Marsigli, C., and Schlemmer, L.: High-Resolution Modelling of the Boundary Layer over complex Terrain, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-170, https://doi.org/10.5194/ems2024-170, 2024.

EMS2024-170

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We investigate the response of the lower atmosphere to resolved and parametrized orographic drag over moderately complex terrain. Typically, larger terrain scales may induce propagating gravity waves and create flow blocking, while smaller scales (less than 5 km) may alter the turbulent atmospheric boundary layer, leading to turbulent orographic form drag (TOFD). Through high-resolution numerical simulations using the ICON model we assess the capability of a sub-grid scale orography (SSO, only its blocking component) and a TOFD parametrizations to replicate the influence of small-scale orographic features on flow over moderately complex terrain.

On one hand, the SSO scheme explicitly addresses a phenomenon where a low-level flow is obstructed by sub-grid scale orography. This obstruction leads to flow separation on the mountain flanks, inducing form drag. Meanwhile, the upper portion of the low-level flow traverses over the orography, concurrently generating gravity waves (which is deactivated for this study). On the other hand, the TOFD parametrization in NWP diagnoses surface stress and the vertical distribution of the resulting momentum flux based on the orography spectrum, relying solely on statistical properties of the orography within the domain, specifically the variance of the sub-grid scale orography. 

For decades, a widely acknowledged length-scale threshold of 5 km has guided atmospheric modelling practices to determine the application of each parametrization (SSO and TOFD). However, as computational capabilities evolve and modelling grids become finer, the validity of this threshold necessitates revaluation. The application of the threshold depends on factors such as model grid resolution, terrain characteristics, and dynamical processes of interest. Therefore, ongoing evaluation and adaptation are essential to ensure its relevance and efficacy.

A series of numerical simulations examines the impact of both parametrizations over moderately complex terrain near the Perdigao and in the Serra daEstrela mountain range. First, simulations ranging from the kilometre to 100-meter scale, are compared with observational data from the intensive observational period (IOP) of the Perdigao field campaign to validate the model. Kilometre-scale ICON simulations in NWP mode, are run continuously for the 49-day IOP. High-resolution Large Eddy Simulations (LES) are run (O 100 m) using  low-resolution (O 1 km) orography to assess the impact of the small-scale orography on the near-surface wind field. The reference impact is compared to the contribution of each parameterization (SSO and TOFD) to the surface drag and the total vertical flux of momentum in the near-surface atmosphere.

The results indicate that even at high resolutions of around 1 km, the effects of the SSO parametrization remain significant, contributing more to total surface stress than the TOFD parametrization. This suggests that the commonly used 5 km threshold may not be applicable in simulations of this nature, underscoring the need for revaluation or refinement of the threshold.

How to cite: Quimbayo-Duarte, J., Schmidli, J., Köhler, M., and Schlemmer, L.: Analysis of Wind Response to Resolved and Parametrized Orographic Drag Across Moderately Complex Terrain, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-901, https://doi.org/10.5194/ems2024-901, 2024.

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Large-eddy simulations (LES) are an important tool in studying meteorological processes on the local scale. However, specific techniques are needed to generate turbulence when initializing these models. While random perturbations in the initial condition might be sufficient for periodic boundaries, their effect will rapidly diminish when performing simulations with open boundaries, which are needed to analyze undisturbed flow over isolated topographic features. Hence, more elaborate techniques are needed to generate and maintain turbulence for such boundaries.

Eddy recycling is one of those turbulent inflow generation techniques and already implemented in atmospheric LES codes such as CM1 and PALM. The eddy recycling method captures the turbulent structures a certain distance downstream of the inflow and injects the captured turbulent field in the inflow region. While eddy recycling successfully generates turbulence in the inflow region, flux profiles are very sensitive to the distance between capture region and injection region as well as the geometry of these regions. In addition, artificial periodicity in the fluxes might be introduced when placing injection region and capture region too close together. The sensitivity of turbulent flux profiles towards the shape of the capture region, the specification of the turbulent field and the effect of artificial periodicity of these fluxes has so far received little attention in atmospheric LES.

To address this issue and investigate the sensitivity of the profile shape of turbulent moments to the specification of the eddy recycling module, a set of idealized LES were conducted for a shear and buoyancy driven atmospheric boundary layer with the Cloud Model 1 (CM1). Each simulation had an identical inflow profile but differed in the shape of the capture region and the distance between the capture and injection region. Preliminary results show that the shape of TKE and variances of wind components as well as temperature is highly sensitive to the shape and location of both capture and injection regions, while average profiles are less affected.

How to cite: Rauchöcker, A. and Stiperski, I.: On the sensitivity of turbulent flux profiles to turbulent inflow generation with the eddy recycling method, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-548, https://doi.org/10.5194/ems2024-548, 2024.

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Atmospheric gravity waves (GW) are small-scale propagating disturbances that arise due to the vertical forcing of air parcels by topography, convection, wind shear, jet streams, frontal systems and other tropospheric sources. GWs play a key role in the transfer of energy, and produce turbulence when they dissipate. This can lead to clear air turbulence (CAT) at higher altitude layers, which is a risk for aviation. GWs can be trapped in the lower atmosphere, propagating only horizontally, in which they can impact the state of the atmosphere. Knowledge about heavy waves (and turbulence) in the boundary layer is still limited and contributes to uncertainties in weather and climate models.

Here we present observations of a strong GW event in the night and early morning of June 30, 2022. The GWs were generated by outflow from a frontal system over the North Sea and Belgium, and reached a large part of the Netherlands. Several wave trains travelled over the Netherlands, with similar direction but distinct phase speed and wavelength. This event was captured by many sensors that are part of the KNMI observational network. From our weather radars, automatic lidar ceilometer and surface observation network the GW propagation properties are determined.  At our Cabauw supersite, part of the Ruisdael Observatory, Doppler lidar and microwave radiometer measurements provide detailed insight in the vertical profiles of the passing GWs. They show fundamental mode ducted GWs, trapped in the lower 500 m with a vertical velocity amplitude up to 3 m/s. Above this altitude, the waves are evanescent and are observed to decay with height. The Doppler lidar also allows us to observe GW-generated turbulence and derive vertical profiles of eddy dissipation rate, due to its high temporal resolution of 1s. Finally, the 200-m mast in-situ observations highlight the influence of the GWs on the meteorological variables, showing large amplitude oscillations in pressure, temperature, relative humidity, wind speed and wind direction.

This comprehensive set of observations may serve as a testbed for high resolution weather models that aim to capture these type of GW events. As this work also highlights the ability to detect GWs by the different components of our KNMI observational network, it provides a starting point to further explore the occurrence and properties of these GWs in the Netherlands, including the North Sea. 

How to cite: Knoop, S., Assink, J., Tijm, S., and Leijnse, H.: High-resolution observations of a gravity wave event over the Netherlands , EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-445, https://doi.org/10.5194/ems2024-445, 2024.

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Air temperature and wind speed observed at reference levels (the former 2 m and the latter 10 m) are essential for validating a performance of meteorological models as well as for parameterizing a boundary-layer processes such as air-sea momentum and heat interactions. This study developed a converting method for wind speed and air temperature observed at a higher level to ones at a reference level, the methods were applied to the data at the Ieodo Ocean Research Station (I-ORS), Korea. The I-ORS is located in the northeast part of the East China Sea, and more than half of typhoons affecting the Korean Peninsula pass near the station. The I-ORS measures wind speed and temperature at 41.4 m and 35.7 m, respectively. Obstacle correction factors was applied to the observed wind speed to reflect the effect of station structure on wind. Then, wind speeds at a reference level with the use of wind speed observed over the rooftop level (41.4 m) was computed by applying the log-wind profile, neural drag coefficient assumption, and power-wind profile methods. The retrieved wind speeds were compared with the observed one at 10 m during the special experiment period. The coefficients for the methods were determined. Air temperature at 2m from the temperature observed at sea surface and rooftop level (35.7 m) was calculated by applying a power-temperature profile. The optimal power for the power profile was determined as different values according to day and night by minimizing errors. 80% of the retrieved temperatures fell within a mean bias less than 0.5°C, while 95% fell within a mean bias less than 1.0°C. The results are expected to contribute to parameterize the air-sea momentum and heat interaction in terms of air temperature and wind speed under strong wind over ocean surfaces. 

Key words: Ieodo Ocean Research Station (I-ORS), reference level temperature, reference level wind speed, air-sea momentum and heat interaction

Acknowledgements: This work is funded by the Korea Hydrographic and Oceanographic Agency (KHOA) and National Institute of Meteorological Sciences (NIMS).

How to cite: Park, M.-S., Baek, K., and Cheong, K.-Y.: Converting a high-level air temperature and wind speed to a reference level ones: Application to the Ieodo Ocean Research Station, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-621, https://doi.org/10.5194/ems2024-621, 2024.

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The atmospheric temperature profile in Arctic winter plays a key role in the observed Arctic amplification of global temperature changes. In the cold season, the Arctic atmospheric temperature and moisture profiles are a product of advection and transformation of air-masses from lower latitudes (Wexler, 1936, Curry, 1983). These poleward flowing air masses cool and dry over several days, losing the majority of their initial heat and moisture content along their trajectory. The occurrence of the resulting transition from an initially cloudy to a radiatively clear state (Stramler et al. 2011, Pithan et al. 2014) proves to be difficult to understand using Eularian, fixed in-space observations (e.g. Becker 2020, Lonardi 2024).

Here we show results from recent controlled meteorological (CMET) balloon (Voss 2012, Roberts et al. 2016) launches from Ny-Alesund, Svalbard. The balloons followed advected air parcels downwind over the ocean beyond the sea-ice edge. CMET balloons can drift at a variable altitude for multiple days along a quasi-Lagrangian trajectory, continuously resolving the vertical structure of the arctic boundary layer (ABL) column.

The observed low level ABL profiles show cooling (2.1 – 2.8K) within few hous after crossing onto the sea ice, leading to decoupling of the surface and an increase in near-surface relative humidity. The inversion layer depens by 100m over the course of 1-2 hours.

The ABL soundings are combined with ice surface temperature satellite imagery to determine the radiative processes driving changes in cloud state and properties. We hypothesise that the boundary layer typically decouples during cold-season on-ice flow within hours of the ice edge, allowing for strong low-level wind-turning. The resulting near-surface flow limits low-level heat and moisture advection towards the central Arctic. According to our hypothesis, intrusions in which the boundary layer remains coupled after crossing the ice edge lead to a much stronger heat and moisture transport towards the central Arctic ocean.

These observations provide a valuable step towards a better understanding of small-scale boundary layer processes, surface energy budgets and their representation in climate models.

How to cite: Schindewolf, J., Pithan, F., and Voss, P.: Tracking arctic boundary layer evolution during on-ice flow using CMET balloons, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-660, https://doi.org/10.5194/ems2024-660, 2024.

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Microclimate within the rural landscape is difficult to predict due to its strong spatial heterogeneity resulting from the juxtaposition landscape elements contrasted in terms of biophysical parameters. Canopy edge is one of the dominant heterogeneities in rural areas, whose influences on microclimate and turbulent structures have mainly been described under neutral thermal stratification.

This study focuses on the micrometeorology over and within a crop-forest transition under unstable atmospheric conditions, when shear and buoyancy have a combined action on turbulence motions within the atmospheric boundary layer (ABL). This study is based on both field and numerical experiments. The field experiment was carried out in Lannemezan (South of France) from March 2023 to March 2024 as part of the MOSAI project (Model and  Observation for Surface-Atmosphere Interactions, https://mosai.aeris-data.fr/). High-frequency sensors were used to measure wind speed and direction, air temperature and humidity, and CO 2 mixing ratio at varying distances from the forest edge. The numerical experiment was performed using a Large Eddy Simulation (LES) atmospheric model, coupled to a one-dimensional multi-layer soil and canopy energy and gas exchanges model. The novelty of this simulation is to resolve both within- and above-canopy turbulence, allowing the characterization of turbulent exchanges during free convection.

We will show how the forest edge flow differs depending on the thermal stability, and the influence of canopy- and ABL-scale motions on the canopy-atmosphere turbulent exchanges. This study is a first step towards simulating micrometeorology over heterogeneous landscapes in unstable conditions. Such detailed simulations should contribute to a better understanding of surface-atmosphere exchanges, and in particular to a better account of surface heterogeneity in meteorological models.

How to cite: Grulois, M., Dupont, S., Irvine, M., and Ogée, J.: Forest edge flows and fluxes under unstable atmospheric conditions., EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-230, https://doi.org/10.5194/ems2024-230, 2024.

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Between the German cities of Höxter and Holzminden, the landscape ascends in the eastern direction from the Weser river at roughly 100 m a.s.l. up to 500 m a.s.l. in the Solling natural area. The slope is forested with deciduous trees with a typical height of approx. 30 m. In order to study the vertical profiles of temperature and wind in the forest, we operated an Unmanned Aerial Vehicle (UAV) flying from ground level up to approx. 100 m agl. Fifteen flights near sunset between summer 2019 and spring 2020 are analysed revealing effects of the foliation and downslope flows. Using rough estimates of turbulent fluxes and sensible heat and momentum based on the vertical profiles allows us to produce leaf area density profiles for the leafy and the leafless case. We compare the results with existing theories both for the average structure of the forest and the vertical profiles.

For the cases studied here, the forest exerts a drag on the wind and the wind decreases markedly in a 30-m-layer above the canopy. The drag is maximal at the upper canopy and the presence of the leaves increases this effect. Due to the slope situation, downslope flows can be detected and enhance the mixing near the surface. Based on the work by Yi [1] we can split the wind speed into contributions from the forest and the slope.

The estimation of turbulent fluxes is rough due to the limited data sample during the flights, but it is in agreement with the profiles of the mean variables. The momentum fluxes as a function of height allows the estimation of the profile of leaf area density as a fingerprint of the average structure of the forest. The results show that for a two storeys forest as present in the our region of interest, assuming a logarithmic profile of the variables does not reflect the measurements.

[1] C. Yi, R. K. Monson, Z. Zhai, D. E. Anderson, B. G. Allwine, A. A. Turnipsseed, S. T. Burns: Modeling and measuring the nocturnal drainage flow in a high-elevation, subalpine forest with complex terrain. Journal of Geophysical Researcj, Vol. 110, D22303 (2005)

How to cite: Wrenger, B. and Cuxart, J.: UAV-based Studies of Temperature and Wind in and above a Deciduous Forest (and a Forest Clearing) in the Region of the Weser Valley, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-992, https://doi.org/10.5194/ems2024-992, 2024.

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The Π Chamber, a turbulent aerosol–cloud reaction chamber, stands as a highly advanced facility for conducting controlled experiments on cloud microphysics. Its unique design enables reproducible and controlled measurements across a broad range of temporal scales, from hours to days, while maintaining consistent thermodynamic conditions. The chamber induces Rayleigh-Bénard convection (RBC), wherein air is heated from below and cooled from above. In this study, we focus on analyzing small-scale temperature fluctuations at selected points along the vertical axis to characterize convection inside the chamber. Understanding these fluctuations is crucial for comprehending the variability in thermodynamic conditions within the chamber, which significantly influences the formation, growth, and evaporation processes at the smallest scales of turbulence.

Our methodology involved collecting high-resolution temperature time series (2 kHz) using the UltraFast Thermometer (UFT) and comparing this data with Direct Numerical Simulations (DNS) conducted under similar thermodynamic conditions. The UFTs, developed at the University of Warsaw, are designed for airborne in-cloud measurements with resolution extending down to scales within and below 1 cm (i.e., reaching the dissipation range). The current sensor version (UFT-2B) features a resistive platinum-coated tungsten wire, 2.5 μm thick and 3 mm long, mounted on a miniature wire probe, facilitating easy replacement of the sensing head. This sensor design allowed for undisturbed vertical temperature profiling spanning from 8 cm above the floor to 5 cm below the ceiling.

The research investigated three distinct temperature gradients (10℃, 15℃, and 20℃) between the top and bottom, maintaining convective conditions inside the chamber. The dataset comprised both long (19 min) and short (3 min) measurement time series, revealing intriguing inhomogeneities near the vertical plates associated with local thermal plume dynamics. We identified two spectral regimes termed inertial and dissipative ranges, characterized by slopes oscillating around -5/3 and -7, respectively. Furthermore, our analysis unveiled a robust relationship between the periodicity of large-scale circulation (LSC) and the temperature gradient, describable by an exponential relation. Notably, the experimental findings demonstrate strong agreement with DNS data, illustrating a rare comparative analysis of this nature.

In our presentation, we will delve into the outcomes of our investigations, engaging in a comprehensive discussion and outlining future research directions.

How to cite: Grosz, R., Shaw, R., Chandrakar, K., and Malinowski, S.: High-resolution temperature profiling in the Π Chamber, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-774, https://doi.org/10.5194/ems2024-774, 2024.

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Vegetation has a strong influence on the interaction between the land surface and the overlying atmosphere, modifying the relative contribution of sensible and latent heat to the surface energy balance (SEB). Vegetation dynamics must be considered to improve atmospheric surface models, especially in the understanding of the land-atmosphere coupling.

Nowadays, remote sensing is an excellent tool to monitor vegetation functioning at different spatial and temporal scales. Spectral indices obtained from remote sensing data, such as the Normalized Difference Vegetation Index (NDVI) are strongly related to photosynthesis and vegetation functioning. Thus, the role of vegetation in the energy partitioning processes could be assessed using these spectral indices.

The Weather Research and Forecast Model (WRF) uses by default monthly values of the Green Vegetation Fraction (GVF) dataset derived from the NDVI of the NOAA Advanced Very High Resolution Radiometer (AVHRR) at 0.144° resolution for the period 1985-1990 to generate its simulations. The overall aim of this work is to integrate monthly MODIS NDVI values at 1 km resolution (MOD13A3 v061 product) in the WRF model to improve simulations. Validation of the simulations will be carried out using an Eddy Covariance flux tower with data from 2017 to the present, which belongs to the GuMNet network (https://www.ucm.es/gumnet), placed in a grassland ecosystem of Central Spain close to a forest influenced by the Guadarrama mountains (El Escorial, Madrid).

Results show that including NDVI in the WRF model improves the simulations in the grassland ecosystem, especially in the estimation of turbulent heat fluxes. Preliminary results in this grassland environment showed that high-resolution NDVI was strongly correlated with latent (a) and sensible (b) heat, especially for three months (May-June-July). These three months coincided when the grassland showed its greatest p changes, presenting its maxima of biomass and then drying quickly during the following months due to the lack of soil water availability.

In conclusion, this work shows that it is essential to include the vegetation dynamics to improve the atmospheric and land surface models, being a first step to use spectral indices as a proxy to improve the models.

How to cite: Cicuéndez, V., Carbone, J., Ortiz-Corral, P., Inclán, R., Román-Cascón, C., Sastre, M., and Yagüe, C.: Integrating MODIS NDVI in the WRF model to improve simulations in the Iberian Peninsula: a case study in a Mediterranean grassland of central Spain., EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-427, https://doi.org/10.5194/ems2024-427, 2024.

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Nocturnal downvalley flows are analyzed in a valley in southern France, near the Pyrenees. Three meteorological stations were installed at different locations strategically chosen in the valley within the framework of the LATMOS-i1 and WINDABL2 projects and in collaboration with the French MOSAI3 project. In addition to the near-surface measurements, including turbulent parameters, several radio soundings during down-valley flow cases were launched during the night to characterize the vertical dynamic and thermal structure of these winds.

Near the surface, downvalley winds are characterized by southerly (from the Pyrenees) and progressively increasing winds, which produce higher values of turbulent parameters than those observed during the day. In addition, the vertical structure of the flow shows significant variations during the night, influenced by a complex interaction between the synoptic conditions and the surface processes. On days with strong synoptic forcing, typically from the west in the study region, downvalley flow formation is completely inhibited. However, on days with moderate synoptic forcing, the north-south orientation of the valley, coupled with the presence of mountains, seems to act as a shield against synoptic winds, allowing the nocturnal downvalley flow to form within the valley in a shallower layer. An analysis of the atmospheric stability using the bulk Richardson number at different layers is also presented. An emphasis is placed on differentiating those layers with higher static/dynamic stability to distinguish whether the turbulence is related to ground-induced thermal effects or dynamically driven by the wind. The analysis is completed by simulations with the WRF model to evaluate its ability to reproduce these events and to point out its shortcomings in order to improve the prediction of these events.

The availability of one year of surface data allows an analysis of the evolution of the structure of these flows over the annual cycle. For this purpose, an algorithm for detecting breeze events and different statistics will be used for their analysis.

This study highlights the complexity of observational studies attempting to differentiate the factors influencing nocturnal downvalley flow, and emphasizes the need to consider both synoptic conditions and surface processes, including the important role played by local topography. 

(1) LATMOS-i project (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?) (PID2020-115321RB-I00, funded by MCIN/AEI/ 10.13039/501100011033).

(2) WINDABL project (PR2022-055). Project to impulse the career of young researchers funded by the University of Cádiz (Spain) (Plan Propio).

(3) MOSAI project (Model and Observation for Surface-Atmosphere Interactions, https://mosai.aeris-data.fr/).

How to cite: Ortiz-Corral, P., Román-Cascón, C., Yagüe, C., Carbone, J., Sun, J., Jomé, M., Lothon, M., Lohou, F., and Jiménez-Rincon, J. A.: Valley Breezes within a valley in Pyrenees: Vertical and Horizontal structure and its Evolution Over the Annual Cycle Through Observations, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-677, https://doi.org/10.5194/ems2024-677, 2024.

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The eastern Ebro basin is composed of an extensive irrigated plain, surrounded by rainfed slopes and wooden mountain ranges and open to the west to the agricultural western Ebro basin. The sea breeze generated at the coast is able to surmount the Catalan Pre-coastal Range through its lowest heights, reaching the basin by its easternmost part. It is a well‐known feature in the region, called Marinada.

A network of Automatic Weather Stations from the Catalan Meterological Service is used here to analyse a period of 19 years (2003–2021). A filtering procedure is developed which selects the events when the Marinada is present, based on detecting clear sky, weak wind conditions and the wind direction from the coast in the afternoon. The analysis of these days show that the Marinada propagates along the basin in the afternoon meanwhile observations of the specific humidity show a sudden increase as the temperature cools down, resulting on a cold and humid advection. It is also found that the timing of the arrival of the Marinada depends on the mesoscale/synoptical circulations already present in the region (westerlies or a thermal low).

Two Marinada events during the LIAISE experimental field campaign during summer 2021 (one with the predominance of westerlies and the other with a thermal low) are further analysed using the MesoNH model. Mesoscale simulations over the Ebro river basin are made at 2km resolution in the horizontal and 4m in the vertical (stretched with height). The initial and lateral boundary conditions are taken from the ECMWF model. Turbulence, radiation and surface parameterizations are taken to properly reproduce the phenomenon. It is shown that the Marinada is a fall wind, generated by a cool marine air mass advected over the Catalan Pre-coastal Range by the action of the sea breeze and the upslope wind. The characteristics and dynamics of the Marinada depend on the synoptical situation. For instance, under thermal low conditions the Marinada is initiated earlier and it is more intense than for the westerlies case. Results also highlight the importance of representing the surface features in the model (such as the irrigation processes) to properly capture the observations of the propagation of the Marinada inland.

How to cite: Jimenez, M. A., Lunel, T. R., Cuxart, J., Boone, A. A., Le Moigne, P., Martinez-Villagrasa, D., and Grau, A.: Characterization of the marine‐air intrusion “Marinada” in the eastern Ebro sub‐basin through observations and mesoscale modelling, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-842, https://doi.org/10.5194/ems2024-842, 2024.

EMS2024-842

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The glacier boundary layer with katabatic down-slope wind strongly governs the exchange of heat between the ice surface and the atmosphere aloft. Glaciers are mostly located in mountainous regions, therefore mountain boundary layer processes (eg., other thermally-driven flows) and dynamically-driven processes such as gravity waves interact with the local glacier boundary layer, leading to disturbance or erosion of it.
In this study, we explore the impact of  dynamically-driven disturbances of the glacier boundary layer with large-eddy simulations. The location of the study is the Hintereisferner glacier in the Austrian Alps. We employ the WRF model at dx=48m to simulate the the evolution of the glacier boundary layer for one day during the HEFEX field campaign in 2018. The day is characterised by  mesoscale cross-glacier flow from the North-West. 
In a second simulation run, we remove the upstream glaciers to validate the impact of the ice surface on the formation of gravity waves. Generally speaking, removing the upstream glaciers leads to a modulation of the gravity waves and a changed sensible heat flux structure over the glacier, a weaker glacier boundary layer, and the propagation of an up-valley flow onto the glacier surface. 
As a final step, we remove all the glaciers from the domain to give an insight on the changed land-atmosphere exchange. The removed glaciers lead to a complete change from a partly stable glacier boundary layer to a convective valley boundary layer disturbed by weaker gravity waves.
This numerical study tries to untangle the processes behind thermally- and dynamically-driven flows in an complex environment and gives possible scenarios for "what to expect” in terms of boundary layer and mesoscale dynamics in a future ice-free catchment area.

How to cite: Goger, B. and Stiperski, I.: The Impact of Changing Ice Surfaces on the Glacier Boundary Layer Structure: A Large-eddy Simulation Case Study from Hintereisferner Glacier, Austria, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-561, https://doi.org/10.5194/ems2024-561, 2024.

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The Korean Integrated Model (KIM), an operational global numerical weather prediction model at the Korea Meteorological Administration, has been developed during the initial phase of the Korea Institute of Atmospheric Prediction Systems (KIAPS) from 2011 to 2019. During this phase, the Noah land surface model (LSM) has been coupled to KIM, and the initial states of the land surface are being generated by a land data assimilation (DA) system based on the National Aeronautics and Space Administration (NASA) Land Information System (LIS). In the ongoing second phase of KIAPS from 2020 to 2026, the Noah-Multiparameterization (Noah-MP) LSM, designed to enhance geophysics representations, has been integrated into the KIM system and is currently undergoing further geophysical advancements.
This study examines the interaction between land surface and atmosphere in the KIM system by estimating a coupling strength between soil moisture (SM) and latent heat flux (LH) represented in LSMs. It is found that improved SM initial conditions through land DA do not ensure improving forecast fields of temperature and specific humidity in the low troposphere in some regions, particularly South Asia croplands, where typically the SM and LH coupling strength is overrepresented in LSMs. Notably, among the sub-components of LH, direct evaporation at the soil surface exhibits stronger coupling with SM than other sub-components. As the overrepresented SM and LH coupling strength may cause degraded performance of land SM DA within land-atmosphere coupled systems, here we aim to analyze and improve the SM and LH coupling representations in LSMs towards improving land DA of the KIM system. In this presentation, we will introduce the sensitivity experiments on LH-related parameters and their impacts on the SM DA performance as well as medium-range weather forecasts.

Acknowledgements. This work was carried out through the R&D project “Development of a Next-Generation Numerical Weather Prediction Model by the Korea Institute of Atmospheric Prediction Systems (KIAPS)”, funded by the Korea Meteorological Administration (KMA2020-02212).

How to cite: Gim, H.-J., Koo, M.-S., Kwon, Y., Cho, M.-H., Song, J., Jun, S., Kim, W., Seol, K.-H., and Kwon, I.-H.: Refinement of coupling strength between soil moisture and latent heat flux: Effects on medium-range weather forecast and soil moisture data assimilation in the KIM system, EMS Annual Meeting 2024, Barcelona, Spain, 1–6 Sep 2024, EMS2024-398, https://doi.org/10.5194/ems2024-398, 2024.

EMS2024-398

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