Warming of Western North Pacific Ocean and Energetics of Transient Eddy Activity

This study examines the increase in the sea surface temperature (SST) in the western North Pacific Ocean (WNPO) during December-February for the period 1959-2008. The relationship of this SST increase with significant interdecadal changes in the baroclinicity and the energetics of transient eddy activity is also examined. These results show that the interannual variations of the WNPO SST and atmospheric conditions including baroclinicity and turbulent heat flux are responses to the upstream atmospheric forcings associated with the East Asian winter monsoon (EAWM). For the interdecadal variations, the intensified baroclinicity downstream of the Pacific storm-track activity is responsible for an increase in the baroclinic energy conversion (BCEC) from the mean available potential energy (MAPE) to the eddy available potential energy (EAPE) to the east of 180 degrees. This in turn increases the BCEC from the EAPE to the eddy kinetic energy (EKE) over this region. The BCEC and generation of EAPE by diabatic heating are enhanced to the east of 180 degrees as a result of the intensified baroclinicity. This could be responsible for the development of transient eddy activity downstream of the Pacific storm track over the North Pacific.