Atmospheric Circulation and Precipitation Fields over the tropical Indo-Pacific Region Associated with the Biennial Oscillation of Sea Surface Temperature

Abstract

Temporal and spatial patterns of atmospheric circulation and precipitation over Indo-Pacific region are analyzed in conjunction with the biennial mode of sea surface temperature anomalies (SSTA). It is investigated how the biennial mode modifies the Asian-Australian monsoon precipitation, which features the seasonal migration of precipitation band. In an attempt to document the impact of the biennial mode on the Asia-Australian monsoon precipitation, two-year cycle variability of SSTA and key atmospheric variables is separated from the seasonal cycle via Cyclostationary EOF (CSEOF) analysis. The monthly Extended Reconstruction SST version 3 (ERSST v.3) and the twentieth century reanalysis version 2 (20CR) are used. The biennial evolution of atmospheric variables is clearly seen over the central Indo-Pacific region (90°-150°E, 20°S-20°N). In boreal summer, local meridional circulation is a distinguishing characteristic over the central Indo-Pacific region, whereas a north-south expanded branch of an intensified zonal circulation develops in austral summer. In boreal summer, low-level anticylonic/cyclonic circulation over the western North Pacific is linked with the northern branch of the local meridional circulation. Essential factors responsible for the distinctive atmospheric responses in the two seasons are the intensity and size of SSTA over the central-eastern Pacific and the different timings of the phase transition in the tropical Pacific and the Indian Ocean. The impact of the biennial mode is clearly different between the two seasons with substantially different impact on the Asian monsoon and the Australian monsoon.