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Hubert Gallée and Guy Schayes

Abstract

The spatial evolution of Antarctic katabatic winds in the area of Terra Nova Bay is examined using the three-dimensional version of the Université Catholique de Louvain-Modèle Atmosphérique Régional (UCL-MAR) mesoscale primitive equation models. The ability of the model to replicate classical linear mountain wave simulations is verified. Then, three-dimensional experiments are performed for the terrain configuration of Terra Nova (Ross Sea coastal zone) using different horizontal resolutions (5, 10, and 20 km). The model converges for resolutions lower than 10 km. Results are in qualitative agreement with available observations and previous modeling work. Strong katabatic winds are simulated with a jet over Terra Nova Bay. The model seems able to initiate the mesocyclonic activity in the Ross Sea due to the katabatic circulation.

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Koen De Ridder and Guy Schayes

Abstract

A model that computes the fluxes of energy and momentum between the land surface and the atmosphere is presented. It is designed to serve as a lower boundary in a mesoscale atmospheric model and is intended to be used to study the influence of the land surface on regional atmospheric circulations and climate.

The land surface model contains one vegetation layer, a soil skin layer, and four subsurface soil layers. The shortwave and longwave radiation schemes are based on the two-stream theory. Turbulent transfer is treated in a very simple manner, by considering canopy–air and ground–air exchanges separately. Plant water flow is governed by differences in water potential between the soil and the leaves. The stomatal resistance formulation uses the effective leaf area index and the leaf water potential as key variables. It is shown that the resulting transpiration scheme implicitly accounts for the influence of visible radiation, soil moisture, atmospheric saturation deficit, and leaf temperature.

The results of four validation experiments are shown. Parameters were chosen prior to the model runs, and no tuning was involved. These experiments show that the surface model is capable of reproducing observed fluxes within instrumental error including timescales ranging from rapid weather changes up to several months.

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Hubert Gallée, Paul Pettré, and Guy Schayes

Abstract

The evolution of summer katabatic wind events over the steep slopes of Adélie Land is examined, with emphasis on the sudden cessation of these events. Different idealized large-scale forcings are considered, including a situation that comes very close to one observed during the IAGO (Interaction Atmosphère Glace Océan) campaign, held in the region in November–December 1985. The hydrostatic meso-γ-scale atmospheric model MAR (Modèle Atmosphérique Régional) is used to assess the sensitivity of the simulated cessation process to a prescribed large-scale forcing.

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