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Communication Dans Un Congrès Année : 2023

Some results from the SOuth west FOGs 3D experiment for processes study (SOFOG3D) project

Julien Delanoë
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Résumé

The primary objective of SOFOG3D, funded by Météo-France and ANR (French National Research Agency), is to advance our understanding of fog processes at the smallest scale to improve forecasts of fog events by numerical weather prediction (NWP) models. A six months field experiment has been conducted from October 2019 to March 2020 in the South-West of France to provide 3D mapping of the boundary layer during fog events. Three nested domains have been instrumented to collect observations from regional scale (300x200 km²) down to local scale on the super-site (10x6 km²). Detailed measurements of meteorological conditions, aerosol properties, fog microphysics, water deposition, radiation budget, heat and momentum fluxes on flux-masts, were performed on the super-site selected in an agricultural exploitation to contrast large open area with pine forest slots. Two 94 GHz cloud radars were operated, and the combination with microwave radiometer (MWR) measurements allowed optimal retrieval of temperature, humidity and liquid water content profiles. In addition in situ measurements of turbulence and droplet size distribution were performed under a tethered balloon. During intensive observation periods, 15 fog events were sampled with the tethered balloon and 180 radiosoundings were launched. A network of 17 observation sites located in forests or crops, has been deployed over a 70x20 km² area to explore the impact of surface heterogeneities on the fog life cycle. A new configuration of the operational NWP model AROME was run with 500 m horizontal resolution, 156 vertical levels and the 2-moment microphysical scheme LIMA. A network of 8 MWR on 6 sites was deployed on the larger domain to evaluate this new configuration and to investigate how better initial conditions of the model can improve fog forecasts through assimilation using an innovative ensemble-based variational data assimilation scheme. High resolution simulations of the three deeper fog layers sampled during the campaign have been performed with the Meso-NH model to assess recent advances in parametrizations and to provide spatio-temporal turbulence and microphysical characteristics of the fog layer and the atmosphere above. Both observations and simulations allowed to better understand the impact of surface heterogeneities (forest vs. non forest) on the fog life cycle. We will present the instrumental set-up and discuss the main results of the project. An overview of the 34 sampled fog events will be given. We will show that the new AROME configuration improves the number of predicted fog cases and reduces the overestimation of thick fog in the current operational configuration, and that the assimilation in the 3D-VAR system of AROME-France of the temperature profiles provided by the MWR network is promising. The data analysis of 17 measurement sites reveals a tendency for a slightly late formation in the forest compared to the crop, related to the shelter effect. The synergy between remote sensing and in situ measurements under the tethered balloon, allowed to document the evolution of thermodynamic and microphysical profiles during the fog life cycle and to study thin to thick fog transition and processes occurring at fog top.
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Dates et versions

meteo-04643796 , version 1 (10-07-2024)

Identifiants

  • HAL Id : meteo-04643796 , version 1

Citer

Frédéric Burnet, Christine Lac, Pauline Martinet, M Haeffelin, Julien Delanoë, et al.. Some results from the SOuth west FOGs 3D experiment for processes study (SOFOG3D) project. 9th International Conference on Fog, Fog Collection and Dew (FOGDEW2023), International Fog and Dew Association (IFDA), Jul 2023, Fort Collins, Colorado, United States. ⟨meteo-04643796⟩
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