Oceanic origin of the interannual and interdecadal variability of the summertime western Pacific subtropical high

Abstract

A recent study found that the western Pacific Subtropical High (WPSH) exhibits both quasi-biennial (2-3 years) and low-frequency (3-5 years) oscillations. While the quasi-biennial oscillation is prominent in 1990s, the 3-5 year oscillation is dominant in 1980s, The two oscillations were attributed to the atmospheric response to the remote forcing of sea surface temperature (SST) in the maritime continent and equatorial central-eastern Pacific, respectively. The present study confirms this hypothesis. When forced by observational SST, the ensemble simulation with the NCAR CAM2 model reasonably reproduces the main characteristics of quasi-biennial oscillation and low-frequency oscillations of the WPSH. The quasi-biennial oscillation is associated with anomalous overturning circulation characterized by enhanced convection over the maritime continent and subsidence over the western North Pacific. The low-frequency oscillation is mainly modulated by remote forcing of SSTA in the equatorial central-eastern Pacific. The model reasonably reproduces the interdecadal transition of the WPSH from low-frequency oscillation in 1980s to quasi-biennial oscillation in 1990s, suggesting that the SST forcing is an essential factor to modulate the interdecadal variation of the WPSH. Copynght 2008 by the American Geophysical Union.