Decadal Variation of the South Asian High: Roles of the Interdecadal Pacific Oscillation and Anthropogenic Aerosols

The South Asian high (SAH) has experienced notable decadal variation over past decades that has exerted substantial influence on the summer climate of the Northern Hemisphere. However, the mechanisms that influence the decadal change of the SAH remain unclear. Results based on reanalysis data and climate model experiments indicate that with increased emission of anthropogenic aerosols (AAs), the contribution of external forcing to the SAH strengthened in the late 1960s and exceeded its internal variability. The transition of the Interdecadal Pacific oscillation (IPO) from the cold to the warm phase and increased AAs jointly promoted decadal decline in the SAH in the late 1970s through air-sea processes and radiation effects, respectively. Notably, the transition of the IPO from the positive to the negative phase around 2000 tended to enhance the SAH. However, this was offset by the larger contribution from high emission of AAs, which promoted a continuously weak SAH. The contribution of AAs might still dominate the SAH changes at the beginning of this century. However, as the emission of AAs declines in the future, the influence of AAs on the SAH might weaken. The IPO is expected to play the dominant role in the decadal variation of the SAH from the 2040s under the low-emission Shared Socioeconomic Pathway (SSP1-2.6).