Interdecadal changes of summer precipitation dominant mode over East Asia-Northwest Pacific around late 1990s

In this study, we investigate the interdecadal variation characteristics of the dominant mode of summer precipitation over East Asia-Northwest Pacific (EA-NWP) before and after late 1990s, reveal the physical mechanism, and address its possible connection with the regional ocean warming background. Study results show that the empirical orthogonal function mode 1 (EOF1) of summer precipitation anomalies over EA-NWP during the global ocean warming acceleration period (1979-1998) present a more significant dipole pattern between Yangtze River Basin (YRB) and tropical NWP compared with that during the global ocean warming slowdown period (1999-2012). And then we find that the anomalous dipoles of low-level winds, geopotential height, convection, and associated wave activity fluxes over NWP significantly shift westward (eastward) and enhance (weaken) in 1979-1998 (1999-2012), which are regarded as the direct cause of the adjustment of dipole pattern between YRB and tropical NWP. Further analysis reveals that the negative sea surface temperature (SST) anomalies in the tropical NWP are prominent (not prominent), resulting in the stronger (weaker) Pacific-Japan Teleconnection over Japan and Tropics in NWP during the period 1979-1998 (1999-2012), and ultimately lead to the change of summer precipitation EOF1 in EA-NWP. By regressing vertical velocity, outgoing longwave radiation, relative vorticity, wave activity fluxes, and precipitation onto the NWP SST in the two periods, the impacts of the SST in the NWP on the interdecadal variation of summer precipitation EOF1 in EA-NWP are verified. Finally, the mechanism diagram of interdecadal variation of summer precipitation is given, which can be useful for short-term precipitation prediction of East Asia.

Automated summary

This study investigates the interdecadal variation characteristics of the dominant mode of summer precipitation over East Asia-Northwest Pacific before and after the late 1990s, revealing the physical mechanism and its connection with regional ocean warming. The results show a significant dipole pattern between Yangtze River Basin and tropical NWP during the global ocean warming acceleration period compared to the slowdown period, with anomalous dipoles of low-level winds, geopotential height, and convection shifting westward and enhancing in the earlier period. Negative sea surface temperature anomalies in the tropical NWP are prominent during the acceleration period, leading to the change in Pacific-Japan Teleconnection and ultimately affecting summer precipitation in EA-NWP.