Tropical Pacific Ocean and the Madden-Julian Oscillation: Role of wind and buoyancy forcing

Abstract

A global ocean circulation model is used to examine the dynamical response of the tropical Pacific Ocean to forcing associated with the Madden-Julian Oscillation (MJO). Model sensitivity experiments first reveal that MJO-related changes in sea level are caused primarily by changes in wind stress. Further, the MJO-related changes in sea surface temperature (SST) are mainly caused by buoyancy (heat) flux in the Indian Ocean, by wind stress in the central tropical Pacific, and by both buoyancy flux and wind stress in the eastern tropical Pacific. Additional model sensitivity studies quantify the tropical Pacific Ocean response to MJO wind forcing. The simulations reveal that the subsurface temperature variations associated with the MJO propagate eastward along the thermocline and rise to the surface in the eastern Pacific. Zonal advection plays a dominant role in SST variation in the central Pacific; vertical advection plays an important role in the evolution of subsurface and surface temperatures in the eastern Pacific. Finally, it is shown that MJO wind forcing can rectify SST variations through nonlinear interactions of the intraseasonal variations of the zonal currents and the zonal SST gradient.