Influence of South Pacific quadrapole on austral winter precipitation over the SPCZ

Abstract

The South Pacific convergence zone (SPCZ) is a key component in the weather and climate system. By analogy to the intertropical convergence zone, the SPCZ is also part of the 'engine' for the tropical convection. There have been many studies about the tropical impacts on the SPCZ. Here, we show that the SPCZ, especially the precipitation in this region, is subject to the influence of South Pacific quadrapole (SPQ) in the subtropics via the mechanism of wind-evaporation-sea surface temperature feedback (SST). The anomalous winds (at 850 hPa) induced by the SST anomaly gradient produce low-level convergence and activate upward motion over the SPCZ region, ultimately leading to deep convection and enhanced precipitation there. As a result, the variability in the SPQ leads the changes in the SPCZ by about 5 months. Such extratropical impacts on the SPCZ are independent of the El Niño/Southern Oscillation, which has been demonstrated to have significant impacts on the SPCZ in existing studies. The process study unveils a new connection between the subtropics in the Southern Hemisphere and the tropics, which can potentially enhance predictive understanding of the SPCZ with obvious implications for the weather and climate system.

Relative Contributions of North and South Pacific Sea Surface Temperature Anomalies to ENSO

“…The first empirical orthogonal function mode of monthly SST anomalies over the North Pacific poleward of 20°N is known as the Pacific Decadal Oscillation (Mantua et al, ; Zhang et al, ), while the first empirical orthogonal function mode of monthly SST anomalies over the South Pacific poleward of 20°S represents an ENSO‐like SST pattern over the South Pacific (Ding, Li, & Tseng, ). The VM pattern is defined as the second empirical orthogonal function mode (EOF2) of monthly SST anomalies over the North Pacific poleward of 20°N (Bond et al, ; Ding, Li, Tseng, Sun, et al, ), and the SPQ pattern is defined as the EOF2 of monthly SST anomalies over the South Pacific poleward of 20°S (Ding, Li, & Tseng, ; Qin et al, ). The second principal component (PC2) time series associated with the VM (SPQ) pattern is normalized to have unit amplitude and is then defined as the VM (SPQ) index.…”