온난역에서의 해양성층화 변화

Abstract

Ocean dynamics in the warm-pool act on the eastward expansion of warm SST through equatorial wave-induced zonal advection, and it also plays a key role to maintain the warm-pool SST through the poleward Ekman transport at the surface layer. Anomalous easterly (westerly) trade winds force the thermocline depth. The trade winds also induce the Ekman upwelling associated the Coriolis effects, which brings the cold water to surface layer in the eastern Pacific. The mean SST over the western Pacific warm pool, where the wind stress variation is small, has experienced a shift from cool state to warm state in recent decades. Increased SST enhances the vertical stratification at the upper level. We examine the changes in the ocean stratification with the SST increase in the warm-pool region for the period 1950-2008. The SSTs analyzed are obtained from the Hadley Centre SST dataset, ERSST,SODA data set. The standard deviation of the zonal wind stress over the region of warm pool core region (120°E­170°E, 10°S­10°N)has gradually increased while the standard deviation of the zonal wind tress has decreased over the central. Zonal wind stress has large variation over the central Pacific. From the empirical orthogonal function analysis of the zonal wind stress, it is found that the center of the wind stress moves westward after the 1997/1998. It may lead to a westward shift of the coupling between SST and winds. Anomalous easterly (westerly) trade winds force the thermocline depth. The trade winds also induce the Ekman upwelling associated the Coriolis effects, which brings the cold water to surface layer in the eastern Pacific. The mean SST over the western Pacific warm pool, where the wind stress variation is small, has experienced a shift from cool state to warm state in recent decades. Increased SST enhances the vertical stratification at the upper level. We examine the changes in the ocean stratification with the SST increase in the warm-pool region for the period 1950-2008. The SSTs analyzed are obtained from the Hadley Centre SST dataset, ERSST,SODA data set. The standard deviation of the zonal wind stress over the region of warm pool core region (120°E­170°E, 10°S­10°N)has gradually increased while the standard deviation of the zonal wind tress has decreased over the central. Zonal wind stress has large variation over the central Pacific. From the empirical orthogonal function analysis of the zonal wind stress, it is found that the center of the wind stress moves westward after the 1997/1998. It may lead to a westward shift of the coupling between SST and winds.