Variabilité thermique et propagation des ondes de Kelvin équatoriales dans l’Océan Atlantique tropical

Abstract

Thermal variability and propagation of equatorial Kelvin waves in the tropical Atlantic Ocean

The interannual variability of Sea Surface Temperature (SST) and the influence of equatorial and coastal Kelvin waves on coastal upwelling are analyzed in the tropical Atlantic Ocean. An interannual simulation forced at the surface by high-frequency winds from the National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR) and at the boundaries by SODA version 2 (Simple Ocean Data Assimilation) was conducted. Model evaluation shows that the mean state and interannual variability of the SST are relatively well represented, despite the warm SST biases observed. These biases are also observed for the majority of interannual simulations in the tropical Atlantic. Spectral analysis of the SST signal suggests that the dynamics of the physical processes governing it are different east of Cape Palmas and east of Cape Three Points. An analysis of longitude-time diagrams of zonal wind stress, thermocline depth and SST at the equator and along the northern coast of the Gulf of Guinea was carried out. The results show a thermocline signature of propagating velocity waves that correspond to equatorial and coastal 2^nd and 3^rd order baroclinic Kelvin waves. No connection between the equatorial upwelling signal and the coastal upwelling north of the Gulf of Guinea is visible in SST, but only in the thermocline. Thus, the effect of the distant wind in propagating equatorial and coastal Kelvin waves is not the primary cause of cold water upwelling at the northern coast of the Gulf of Guinea. Rather, these equatorial and coastal waves, generated after the intensification of winds in the western part of the basin, carry a signal of basin-wide adjustment of the thermal structure.

Keywords: Sea Surface Temperature ; Coastal upwelling ; Equatorial and coastal Kelvin waves ; Tropical Atlantic Ocean ; Gulf of Guinea.