Ocean response to strong precipitation events in the Gulf of Lions (northwestern Mediterranean Sea): a sensitivity study |
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| Authors: | Cindy Lebeaupin Brossier Karine Béranger Philippe Drobinski |
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| Institution: | 1.Laboratoire de Météorologie Dynamique (CNRS/Ecole Polytechnique/ENS/UPMC),Institut Pierre Simon Laplace,Palaiseau,France;2.Unité de Mécanique,école Nationale Supérieure de Techniques Avancées (ENSTA)—ParisTech,Palaiseau,France |
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| Abstract: | The Mediterranean Sea is a region of intense air–sea interactions, with in particular strong evaporation over sea which drives
the thermohaline circulation. The Mediterranean region is also prone to strong precipitation events characterized by low spatial
extent, short duration, and high temporal variability. The impacts of intense offshore precipitation over sea, in the Gulf
of Lions which is a spot for winter deep convection, are investigated using four sensitivity simulations performed at mesoscale
resolution with the eddy-resolving regional ocean model NEMO-MED12. We use various atmospheric fields to force NEMO-MED12,
downscaled from reanalyses with the non-hydrostatic mesoscale Weather Research and Forecasting model but differing in space
resolutions (20 and 6.7 km) or in time frequencies (daily and three-hourly). This numerical study evidences that immediate,
intense, and rapid freshening occurs under strong precipitation events. The strong salinity anomaly induced extends horizontally
(≃50 km) as vertically (down to 50 m) and persists several days after strong precipitation events. The change in the space
resolution of the atmospheric forcing modifies the precipitating patterns and intensity, as well as the shape and the dynamics
of the low-salinity layer formed are changed. With higher forcing frequency, shorter and heavier precipitation falls in the
ocean in the center of the Gulf of Lions, and due to a stronger vertical shear and mixing, the low-salinity anomaly propagates
deeper. |
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