The summer western north Pacific subtropical high (WNPSH)—part of Pacific–Japan pattern—regulates the summer monsoons of South China Sea (SCS) and East Asia. Previous studies noted how sea surface temperatures (SSTs) in Indian and Pacific Ocean affect the WNPSH intensity via atmospheric equatorial wave dynamics. Also, internal atmospheric dynamics associated with upper-tropospheric Eurasian Rossby wave train inducing Rossby wave breaking controls WNPSH. However, the relative impacts of remote SST and internal atmospheric variability on WNPSH remain unknown. Here, we investigate the contributions of internal atmospheric variability and remote SST forcing to WNPSH interannual variability during summer using reanalysis and Atmospheric Model Intercomparison Project (AMIP) outputs. We found that internal atmospheric variability and remote SSTs contribute around 70% and 30% to geopotential height variability in the lower tropospheric WNPSH, respectively. Also, internal atmospheric variability and SST each contributes to 50% of lower-tropospheric equatorial zonal wind variability over SCS at the southern portion of WNPSH. The results suggest more attention should be paid to internal atmospheric variability to understand the summer WNPSH dynamics and its future forecast predictability.

Indian Ocean,western Pacific subtropical high,pacific ocean,atmospheric internal variability,Summer Sea Surface Temperature