The response of the Ligurian and Tyrrhenian Seas to a summer Mistral event: A coupled atmosphere–ocean approach

Abstract

In this paper the effect of a summer Mistral event on the Ligurian and Tyrrhenian Seas in the northwestern Mediterranean is discussed, using a coupled numerical model and satellite and in situ observations. The focus is on the spatial and temporal distribution of the ocean mixed layer response to the strong winds, and on how this is affected by atmosphere-ocean coupling. The model used is the Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS Ò1), developed at the Naval Research Laboratory. This system includes an atmospheric sigma coordinate, non-hydrostatic model, coupled to a hydrostatic sigma-z level ocean model (Naval Coastal Ocean Model), using the Earth System Modeling Framework (ESMF). The model is run at high (km scale) resolution to capture the fine structure of wind jets and surface cooling. Two non-assimilating numerical experiments, coupled and uncoupled, are run for a 3-day period of a Mistral event, to examine more closely the impact of coupling on the surface flux and sea surface temperature (SST) fields. The cooling of SST up to 3°C over 72 h in the coupled run significantly reduced the surface momentum and heat fluxes, relative to the uncoupled simulation, where the SST was kept fixed at the initial value. Mixed layer depths increase by as much as 30 m during the event. A heat budget analysis for the ocean is carried out to further explain and investigate the SST evolution. Shear-induced mixing in inertial waves is found to be important to the surface cooling. Effects of coupling on the atmospheric boundary layer are found to be significant, but overall the effect of coupling on the synoptic low pressure system is small.

Mistral and Tramontane wind speed and wind direction patterns in regional climate simulations

“…When taking into account that QuikSCAT shows higher wind speeds than the buoy in the Gulf of Lion, these spatial patterns are robust (tested with a wind speed dependent QuikSCAT bias, not shown). Close to the eastern coast of the Gulf of Lion, intensified cooling has been observed during Mistral events and in coupled simulations (Small et al 2012;Schaeffer et al 2011). Renault et al (2012) studied a Tramontane event in coupled simulations and found a decreasing sea surface temperature in the western part of the Gulf of Lion.…”

Lagged effects of the Mistral wind on heavy precipitation through ocean-atmosphere coupling in the region of Valencia (Spain)

“…The atmospheric model within the MORCE system is the non-hydrostatic weather research and forecasting model (WRF) version 3.1.1 of the National Center for Atmospheric Research (NCAR) (Skamarock et al 2008). The domain covers the Mediterranean basin in line with COR-DEX requirements with a horizontal resolution of 20 km.…”

Seismic reflection imaging of shallow oceanographic structures

“…The top of the seasonal thermocline is typically located at depths between 25 and 45 m [ Jurado et al ., ]. In the Tyrrhenian Sea, similar stratification strength can be found [ Small et al ., ], and depths as shallow as 15–30 m are reached as early as May [ D ' Ortenzio et al ., ]. At the other extreme, off the coasts of Florida, the top of the seasonal thermocline occurs deeper, around 100 m in November [ SAIC , ].…”