Impact of the Ocean Mixed Layer Diurnal Variations on the Intraseasonal Variability of Sea Surface Temperatures in the Atlantic Ocean

Abstract

his study investigates the nonlinear processes by which the ocean diurnal variations can affect the intraseasonal sea surface temperature (SST) variability in the Atlantic Ocean. The Centre National de Recherches Météorologiques one-dimensional ocean model (CNRMOM1D) is forced with the 40-yr ECMWF Re-Analysis (ERA-40) surface fluxes with a 1-h frequency in solar heat flux in a first simulation and with a daily forcing frequency in a second simulation. This model has a vertical resolution of 1 m near the surface. The comparison between both experiments shows that the daily mean surface temperature is modified by about 0.3°?0.5°C if the ocean diurnal variations are represented, and this correction can persist for 15?40 days in the midlatitudes and more than 60 days in the tropics. The so-called rectification mechanism, by which the ocean diurnal warming enhances the intraseasonal SST variability by 20%?40%, is found to be robust in the tropics. In contrast, in the midlatitudes, diurnal variations in wind stress and nonsolar heat flux are shown to affect the daily mean SST. For example, an intense wind stress or nonsolar heat flux toward the atmosphere during the first half of the day followed by weak fluxes during the second half result in a shallow mixed layer. The following day, the preconditioning results in heat being trapped near the surface and the daily mean surface temperature being higher than if these diurnal variations in surface forcings were not resolved.