Response of the South Asian High in May to the Early Spring North Pacific Victoria Mode

Abstract

Abstract The interannual variability of the South Asian high (SAH) in May plays an important role in the evolution of the Asian summer monsoon. In this study, reanalysis data and an atmospheric general circulation model are employed to investigate the response of the SAH in May to the early spring North Pacific Victoria mode (VM) on an interannual time scale. Observational results indicate a robust linkage between the early spring VM and the SAH position in May, even if the El Niño and Indian Ocean basin model (IOBM) signals are removed. When the early spring VM is in its positive phase, a zonally divergent circulation anomaly in the upper troposphere forms with tropospheric divergence over the tropical eastern Pacific and anomalous convergence over the South China Sea–Maritime Continent region. As a result, westerly anomalies associated with the zonally divergent circulation anomaly appear in the upper troposphere over the Indian Ocean–Indochina Peninsula that impede the northwestward movement of the SAH in May. When the early spring VM is in its negative phase, the opposite conditions occur. Three sets of numerical experiments were performed to verify the key physical process revealed in the observational results. The early spring VM is a reliable indicator of the interannual variability of the SAH position in May.