Two‐way one‐dimensional high‐resolution air–sea coupled modelling applied to Mediterranean heavy rain events

Abstract

South-eastern France is prone to heavy rain events during the autumn. For these extreme precipitation events, the Mediterranean Sea fuels the atmospheric boundary layer in heat and moisture and sometimes contributes to flooding, owing to the large swell and waves produced in these situations. The aim of this study is to examine how the severe atmospheric conditions over the sea associated with these events alter the ocean mixed layer, and what feedback the ocean contributes to the precipitation events.To address these questions, a high-resolution air-sea coupled system is developed between the atmospheric MESO-NH model and a one-dimensional ocean model. It is applied for short range (24 h) and high-resolution (2-3 km) simulations of three representative torrential rainfall events: 12-13 November 1999 (Aude case), 8-9 September 2002 (Gard case) and 3 December 2003 (Hérault case). In those meteorological situations characterized by moderate to intense low-level winds, the Mediterranean Sea globally loses energy, to the benefit of the convective precipitating systems. The result is an overall decrease of the thermal content all along the simulation of the events. Significant cooling and deepening of the ocean mixed layer are found in the areas of intense low-level winds. A notable result of the study concerns the impact of the torrential rainfall on the ocean mixed layer. The most important disturbances of the ocean mixed layer are indeed found underneath the heavy precipitation. The salt content is decreased all along the ocean mixed layer depth, but more significantly in the first ten metres near the air-sea interface, with the formation of a salt barrier.By performing both two-way and one-way coupled simulations, it is found that the interactive coupling tends to moderate both the atmospheric and ocean responses compared with the one-way mode. The differences between the two-way and one-way coupled simulations are, however, found to be relatively small considering the atmospheric short-range forecast.

Ocean Mixed Layer responses to intense meteorological events during HyMeX-SOP1 from a high-resolution ocean simulation

“…In response to strong low-level wind blowing towards the coasts during HPEs, a rapid sea level rise may be observed and significantly amplify the flooding by countering the river runoff to the sea (Lebeaupin Brossier et al, 2009a. Sometimes, at the same time, due to heavy rainfall, a rapid surface freshening occurs (Lebeaupin Brossier et al, 2009a,b, 2012.…”

Classifying severe rainfall events over Italy by hydrometeorological and dynamical criteria

“…On one hand, efforts have been devoted to the assessment of the predictive ability of meteorological models with respect to severe rainfall events (Petroliagis et al, 1997;Romero et al, 2005;Hohenegger et al, 2006Hohenegger et al, , 2008Davolio et al, 2007;Schär, 2007a, 2007b;Argence et al, 2008;Lebeaupin et al, 2008;Amengual et al, 2009;Lapeyre and Talagrand, 2009): their goal is to evaluate how closely a particular model can predict the true state of a certain severe rainfall scenario as a function of observational data quality and availability, parametrization of the subgrid processes, model coupling, model approximations and resolution. On the other hand, some studies have investigated the dynamical, kinematical and microphysics properties of observed systems (Leckebusch and Ulbrich, 2004;Grazzini, 2007;Miglietta and Regano, 2008;Sanchez-Gomez et al, 2008).…”

Numerical study of the October 2007 flash flood in the Valencia region (Eastern Spain): the role of orography

“…Numerous numerical modelling experiments on flash-floods have been conducted in this area in recent years. Some of these experiments have been focused on sensitivity testing (Federico et al, 2008;Bresson et al, 2009), development of forecasting systems (Davolio et al, 2009), air-sea interaction processes (Pastor et al, 2001;Lebeaupin et al, 2006Lebeaupin et al, , 2009 or investigation of the mechanisms involved in heavy rain events (Miglietta and Regano, 2008).…”