Role of the Northeast Winter Monsoon on the Biennial Oscillation of the ENSO/Monsoon System

Abstract

The diagnostic study of the biennial oscillation (BO) of the ENSO/monsoon system is performed by using the sea surface temperature (SST), sea surface wind, sea level pressure, and outgoing longwave radiation data. The BO is a prominent feature of the ENSO/monsoon system that results in the modulation of convective activity aroud the maritime continent. The BO tends to change its anomalous states during the Northern Hemisphere spring. The SST variation around the South China Sea also has a BO with a phase transition that tends to occur about a half year earlier, that is, during the Northern Hemisphere autumn. The intensification of the northeast winter monsoon (NEWM) probably modifies the anomalous state of the SST which persists until the northern summer. The SST anomalies around the South China Sea are favorable for modifying the convective activity around the maritime continent during the northern winter to summer. The strength of the convective activity further regulates the SST anomalies in the tropical central-eastern Pacific through the Walker circulation during the northern summer to winter. This anomalous SST state is probably responsible for the strength of the NEWM by controlling the extratropical circulation pattern. The NEWM changes the anomalous state of the SST around the South China Sea. Thus the cycle of the BO of the ENSO/monsoon system is completed. It is, thus, strongly suggested that the tropical-extratropical interaction plays an essential role in the BO of the ENSO/monsoon system.