Response of the Pacific and Atlantic oceans to interannual variations in net atmospheric freshwater

Abstract

The response of the Pacific and Atlantic Oceans to net atmospheric freshwater (evaporation minus precipitation (EmP)) between 1988 and 2000 was studied using a global ocean general circulation model developed in the Massachusetts Institute of Technology. Evaporation estimates from the Goddard Satellite Surface Turbulent Fluxes and precipitation estimates from the Global Precipitation Climatology Project were used. Model simulations showed that the spatial distribution of the average sea surface salinity (SSS) changes during the 1988–2000 period resembled that of average EmP changes, because SSS changes were primarily associated with anomalous vertical mixing forced by the anomalous EmP. The spatial distribution of average near‐surface temperature anomalies, however, was different from those of average EmP and SSS anomalies. Analyses indicated that temperature changes in the subtropical North and South Pacific resulted from anomalous heat advection which, in turn, resulted from changes in the subtropical gyre circulations. Temperature changes in the tropical Pacific were associated with anomalous heat advection due to changes in the South Equatorial Current (SEC). Furthermore, the changes in the subtropical gyres and the SEC resulted largely from anomalous EmP in the subtropical Pacific. Temperature changes in the Atlantic, however, were largely associated with vertical mixing changes due to anomalous EmP. Observed interannual variations of SSS in the Western Pacific Warm Pool were simulated successfully. A large difference between simulated and observed SSS, however, was found in the central equatorial Pacific. Simulated SSS and temperature varied at interannual and longer timescales in most of the Pacific and Atlantic Oceans. Large changes in SSS and temperature due to anomalous EmP in the Pacific and Atlantic strongly suggest that EmP variability can play an important role in ocean and climate variabilities at interannual and longer timescales.