Response of the Western Tropical Pacific to the Asian Winter Monsoon: The Generation of the Mindanao Dome

Abstract

We have investigated the evolution of the Mindanao Dome off the Philippine coast using the GFDL ocean model. It is found that the model's Mindanao Dome evolves in late fall due to local upwelling when a positive curl associated with the northeast Asian winter monsoon increases over the region. It expands eastward with a recirculation composed of the North Equatorial Current in the north, the Mindanao Current in the west, and the North Equatorial Countercurrent in the south. After reaching a maximum in winter, it begins to decay in spring due to an intrusion of downwelling long Rossby waves excited in winter by the northeast trade winds farther eastward near 160°E, as well as a retreat of the local positive wind-stress curl. Further control runs demonstrate that the variation of the model's Mindanao Dome is almost perfectly determined by the change of the wind field in the western Pacific west of the date line. A possible link between the Asian winter monsoon and the seawater temperature anomaly in the western Pacific appears to be the origin of the biennial oscillation of the heat content anomaly in the western tropical Pacific. This study suggests that the Asian monsoon system, i.e., the air?sea?land system, may strongly regulate oceanic conditions both seasonally and interannually in the tropical Pacific west of the date line.