Impact of a medicane on the oceanic surface layer from a coupled, kilometre-scale simulation

Abstract

<jats:p>Abstract. A kilometre-scale coupled ocean-atmosphere numerical simulation is used to study the impact of the 7 November 2014 medicane on the oceanic upper layer. The processes at play are elucidated through analyses of the tendency terms for temperature and salinity in the oceanic mixed layer. Whereas comparable by its maximum wind speed to a Category 1 tropical cyclone, the medicane results in a substantially weaker cooling. As in weak to moderate tropical cyclones, the dominant contribution to the surface cooling is the surface heat fluxes, with secondary effects from the turbulent mixing and lateral advection. Upper-layer salinity decreases due to heavy precipitation that overcompensates the salinizing effect of evaporation and turbulent mixing. The upper-layer evolution is marked by several features believed to be typical of Mediterranean cyclones. First, strong, convective rain occurring at the beginning of the event build a marked salinity barrier layer. As a consequence, the action of surface forcing is favoured and the turbulent mixing dampened, with a net increase of the surface cooling as result. Second, due to colder surface temperature and weaker stratification, a cyclonic eddy is marked by a weaker cooling, oppositely to what is usually observed in tropical cyclones. Third, the strong dynamics of the Sicily Strait enhances the role of the lateral advection in the cooling and warming processes of the mixed layer. </jats:p>

Reply to Referees RC1 and RC2

“…Lebeaupin Brossier et al, 2009Rainaud et al, 2017) and is comparable to other high-wind or medicane events (e.g. Renault et al, 2012;Bouin and Lebeaupin Brossier, 2020a be underestimated by the model (−0.6°C in 24 hours and −0.85°C in 42 hours simulated by AOW). Overall, this default in representing the cooling can be explained by the initial ocean state with a too smooth thermocline that limits the mixed-layer cooling by entrainment, by physical parameters and/or schemes in NEMO and by the absence of ocean-wave coupling.…”

Reply to Referees RC1 and RC2

“…Lebeaupin Brossier et al, 2009Rainaud et al, 2017) and is comparable to other high-wind or medicane events (e.g. Renault et al, 2012;Bouin and Lebeaupin Brossier, 2020a be underestimated by the model (−0.6°C in 24 hours and −0.85°C in 42 hours simulated by AOW). Overall, this default in representing the cooling can be explained by the initial ocean state with a too smooth thermocline that limits the mixed-layer cooling by entrainment, by physical parameters and/or schemes in NEMO and by the absence of ocean-wave coupling.…”

Role of moist and dry air advection in the development of Mediterranean tropical‐like cyclones (medicanes)

“…Gaertner et al (2017) suggested that the effects of air-sea interaction on medicanes may depend on the oceanic mixed layer depth, while Ricchi et al (2017) found that the surface roughness from wave motion significantly affected the November 2011 case. Bouin and Lebeaupin Brossier (2020) identified strong control of sea-surface temperature (SST) on latent heat fluxes, which maintained convection in the November 2014 case. Miglietta et al (2011) and Pytharoulis (2018) investigated the impact of a uniform SST change for two different medicanes (September 2006 andNovember 2014), agreeing that warmer (colder) SSTs lead to more (less) intense cyclones, but only for changes above ±2 • C.…”