ACINN Graduate Seminar - WS 2025/26
2025-10-15 at 12:00 (on-line and on-site)
MOSAI project: motivations, objectives, strategy and some results
Fabienne Lohou, Emilie Bernard, Sylvain Dupont et Alice Maison
University of Toulouse, Météo-France, National Research Institute for Agriculture, Food and Environment, École nationale des ponts et chaussées
The land surface impacts the atmosphere from daily to seasonal time scales. An accurate assessment of the land–atmosphere exchanges, and their correct representation in surface schemes, are therefore essential for weather and climate forecasts. However, Earth System and Numerical Weather Prediction models often have large biases in their representation of surface–atmosphere fluxes when compared to observations. The Model and Observation for Surface–Atmosphere Interactions over heterogeneous landscape (MOSAI) project aims at improving modeling and estimating surface fluxes, with a focus on the impact of surface heterogeneity. The objectives and strategy of the MOSAI project will be presented, illustrated by some results.
A framework is set up to assess land-atmosphere coupling at the process scale and revisit its representation, particularly in the presence of surface heterogeneities that are ubiquitous on the Earth's continents. The first step consists in creating a set of singlecolumn model setups with a homogeneous land surface, that share the same atmospheric initial state and boundary conditions but differ by the physiographic properties of the land surface. The ability of ARPEGE-SURFEX to capture the processes occurring at the landatmosphere interface is evaluated using measurements collected during the BLLAST campaign, complemented for the description of the atmospheric boundary layer by largeeddy simulations run under the exact same setup with the Meso-NH model.
To work on physical parameterizations, a framework based on the comparison between climate or NWP models in a single-column model (SCM) configuration and large eddy simulations (LES) is usually used. In these study cases, surface conditions are generally prescribed with fixed surface fluxes and temperatures, blocking the feedbacks between the atmosphere and the surface. Besides, in coupled configuration, the models may have different surface schemes, which are often complex and difficult to replace. We will present the development of a modeling framework based on a case study based on the MOSAI campaign, a similar simulation set-up between 1D and LES, and , a common simplified surface model.
Micrometeorological simulations have been conducted over alternating agricultural and forested plots to better understand how surface heterogeneities influence the turbulent exchanges between land and atmosphere under different thermal stratifications. Using a high-resolution LES, the results highlight the multi-scale effects of surface heterogeneity — from the fine micrometeorology within the forest all the way up to the atmospheric boundary layer. These novel simulations provide opportunities for developing more accurate representations of surface heterogeneities in weather and climate models.
The content of this webpage is the author’s opinion and the author’s intellectual property. ACINN has the author’s consent to make this information available on the webpage for the announcement of the seminar presentation and in the seminar archive.