Abstract
Abstract. This study investigates the mechanisms acting at the air–sea interface during a heavy precipitation event that occurred between 12 and 14 October 2016 over the north-western Mediterranean area and led to large amounts of rainfall (up to 300 mm in 24 h) over the Hérault region (southern France). The study case was characterized by a very strong (>20 m s−1) easterly to south-easterly wind at low level that generated very rough seas (significant wave height of up to 6 m) along the French Riviera and the Gulf of Lion. In order to investigate the role of the waves on air–sea exchanges during such extreme events, a set of numerical experiments was designed using the Météo-France kilometre-scale AROME-France numerical weather prediction model – including the WASP (Wave-Age-dependant Stress Parametrization) sea surface turbulent flux parametrization – and the WaveWatch III wave model. Results from these sensitivity experiments in the forced or coupled modes showed that taking the waves generated by the model into account increases the surface roughness. Thus, the increase in the momentum flux induces a slowdown of the easterly low-level atmospheric flow and a displacement of the convergence line at sea. Despite strong winds and a young sea below the easterly flow, the turbulent heat fluxes upstream of the precipitating system are not significantly modified. The forecast of the heaviest precipitation is finally modified when the sea state is taken into account; notably, in terms of location, this modification is slightly larger in the forced mode than in the coupled mode, as the coupling interactively balances the wind sea, the stress and the wind.
Highlights
The western Mediterranean region is regularly affected by heavy precipitation events (HPEs) that are characterized by a large amount of rainfall over a small area in a very short time; these events can lead to flash flooding, causing severe damage and, in some cases, casualties (e.g. Delrieu et al, 2005; Llasat et al, 2013)
These differences in the precipitation forecasts highlighted the indirect impacts of taking the sea state into account: a modification of the position of the convergence line at sea related to the speed of the low-level easterly flow, followed by a small modulation of the intensity of the associated convection which was likely due to differences in term of heat fluxes upstream over the Ligurian Sea
This study investigated the role of the representation of the sea state during the HPE that occurred between the 12 and 14 October 2016 south of France
Summary
The western Mediterranean region is regularly affected by heavy precipitation events (HPEs) that are characterized by a large amount of rainfall over a small area in a very short time; these events can lead to flash flooding, causing severe damage and, in some cases, casualties (e.g. Delrieu et al, 2005; Llasat et al, 2013). Recent studies have implemented different formulations in order to better account for the sea state and the sea spray effect on the sea surface roughness and heat and momentum fluxes during extreme events, such as Hurricane Arthur (Garg et al, 2018) or medicanes (Mediterranean tropical-like cyclones; Rizza et al, 2018). They showed that including the surface wave effects significantly improved the simulated track as well as the intensity and the maximum wind speed of the storm.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
