Decadal shift in summer precipitation variability over East Asia in the mid-2000s and wave propagation toward North America


East Asian summer climate displays a marked change after the late 1990s. This is principally due to a weakening of the Pacific-Japan (PJ) teleconnection pattern that was a dominant driver of precipitation variability over East Asia. Nevertheless, western Japan has frequently experienced hevy rainfall events over the past several years. Atmospheric reanalysis and observational datasets are used to investigate summer precipitation variability over East Asia in a view of interdecadal changes from 1979 to 2020.
East Asian summer precipitation has increased the most in Japan, especially over around the Southwest Islands in southern Japan, where cumulus convection has been more dominant for the characteristic of precipitation variability including meiyu-baiu rainfall than frontal structure since the mid-2000s. Atmospheric analysis in vertical structures and convective instability indicates that moist instability is neutralized by cumulus convection over the southern East China Sea and off the Pacific coast of Japan, where recent warming in sea surface temperature (SST) along the Kuroshio exceeds the SST threshold for convection. This decadal shift in precipitation variability has a close relationship with the second precipitation mode over East Asia, which has taken the place of the PJ pattern as a leading driver of precipitation variability over western Japan in the past decade. The enhanced cumulus convection enables to act as a forcing for Rossby wave train from East Asia towards North America along the westerly jet or for the eastward extension of the Silk-Road pattern, which possibly favors heat wave in the Pacific northwest areas of North America.