The Interdecadal Changes of the Relationship Between May‐June and July‐August NWPSH and Their Physical Mechanisms.

Unlike prior researches focusing on interannual or interdecadal changes of the Northwest Pacific subtropical high (NWPSH), this paper emphasizes the interdecadal changes in the relationship between May‐June and July‐August NWPSH. The correlation coefficients between them are 0.66 (passing the 99.9% confidence level) and 0.12 during 1979–2002 and 2003–2023. Therefore, the May‐June NWPSH has a strong connection with July‐August East Asian precipitation during 1979–2002, but not during 2003–2023. The interdecadal variations in the relationship of NWPSH are due to interdecadal changes of ENSO. During 1979–2002, the eastern‐type ENSO in prior winter, having longer durations, can influence May‐June and July‐August NWPSH and the North Indian Ocean. However, the central‐type ENSO in prior winter only persists it's influence until May‐June, and changes into a Pacific Dipole pattern in July‐August during 2003–2023. Despite the North Indian Ocean continually warms during 2003–2023, the tropical Pacific Dipole offsets its impacts on the NWPSH. Plain Language Summary: The Northwest Pacific Subtropical High (NWPSH) has always been valued by meteorologists due to its important role in the East Asian climate. This paper found that the relationship between the NWPSH in May‐June and July‐August has weakened significantly since 2002. The eastern‐type ENSO, characterized by longer durations, can influence the NWPSH and the North Indian Ocean in May‐June and July‐August before 2002. However, from 2003 to 2023, the influence of the central‐type ENSO only persists until May‐June, transitioning to a Pacific Dipole pattern in July‐August. Therefore, both May‐June and July‐August NWPSH are affected by the North Indian Ocean before 2002. However, the NWPSH in May‐June is affected by the North Indian Ocean and prior winter ENSO after 2002, while the July‐August NWPSH is impacted by the tropical Pacific Dipole. And the tropical Pacific Dipole also offsets the influence of the North Indian Ocean on the NWPSH. This leads to a weakening of the relationship between the NWPSH in May‐June and July‐August. Key Points: The relationship between the Northwest Pacific subtropical high (NWPSH) in May‐June and July‐August has significantly weakened after 2002The reason for weakening relationship of NWPSH is that the persistent eastern ENSO has become a short‐period central ENSO after 2002Central ENSO will become Pacific Dipole mode in summer, which will weaken the influence of North Indian Ocean on NWPSH [ABSTRACT FROM AUTHOR]