Abstract : 2E.1
Ocean-atmosphere interactions and coupling associated with torrential rainfall events

Cindy Lebeaupin Brossier, Véronique Ducrocq, Hervé Giordani
GAME/CNRM (Météo-France, CNRS)

The mountainous areas surrounding the Mediterranean nearly-closed sea basin are prone to torrential rainfall in autumn. The Mediterranean Sea is an important source of heat and moisture for these extreme events. Generally, an unstable air mass is transported by a strong low-level wind from the sea towards the relief. The convection is then triggered and could stay several hours over the same area, producing large rainfall totals.

The sensitivity of these extreme events to the sea surface conditions has been examined based on high-resolution atmospheric simulations (2-3 km) on three heavy rainfall cases over Southern France (12-13 Nov. 1999 over Aude, 8-9 Sept. 2002 over Gard, 3 Dec. 2003 over Hérault). Various SST fields have been used for the atmospheric MESO-NH simulations. We also introduced two iterative bulk sea surface fluxes parameterizations in the MESO-NH surface scheme (SURFEX): the UNITFP parameterization including a multi-campaign calibration of the exchange coefficients and the COARE 3.0 algorithm (Fairall et al., 2003). The main results are: first, the significant impact on the atmospheric convection intensity and location of the overall SST value beneath the low-level jet that impinge the relief; secondly a strong decrease of the wind stress and of the evaporation simulated when the bulk iterative parameterizations are used instead of the standard MESO-NH parameterization.

As a second part of this study, an air-sea coupled modelling between the MESO-NH model and the 1D oceanic model in turbulent kinetic energy equations based on Gaspar et al. (1990) is currently developed in order to study the impact of heavy precipitation and associated strong wind stress on the Mediterranean Sea mixed layer. Some insights about this coupling development and about its impacts on the same torrential rainfall events simulations will be presented during the conference.