Séminaire
The sea surface temperature prognostic scheme of Zeng and Beljaars (2005) developed to represent diurnal warming is extended to represent rain-induced freshening and cooling. Effects of rain on salinity and temperature in the molecular skin layer and the near surface (first meters) turbulent layer are separately parameterized by taking into account rain sensible heat and freshwater fluxes, additional surface stress and penetrating droplets induced mixing. The scheme results are compared to two observational cases that also provide information on the near-surface stratifications from a thermistor chain during PALAU2013 campaign and from the Surface Salinity Profiler (SSP) during Kilo Moana 2011 campaign. Compared to previous idealized computations with an ocean mixed layer model, this simple scheme reproduces the dependency of salinity on wind and rainfall rate and the lenses lifetime. It produces temperature variations consistent with observation by surface drifters. It is in addition sensitive to the peak rainfall for a given amount of rain and it reproduces the observed lag between temperature and salinity minimum at low wind speed. Finally, a first assessment of the impact of these fresh lenses on ocean surface variability is given for the near equatorial western Pacific. In particular, the mean rain-induced cooling can be compared to the diurnal warming and they both impact large-scale horizontal surface temperature gradients. The present parameterization can be used in variety of models to study the impact of rain-induced fresh and cool lenses at different spatial and temporal scales.