Abstract

This study investigated the characteristics of regular and irregular seasonal northward march of East Asian summer wet environment (SNM_EASWE) over the continent during June–July over the past six decades and in the future. During 1961–2015 and in the future, the regular SNM_EASWE is defined mainly by an intensified climatic northward-moving rainband over eastern China, whereas the irregular SNM_EASWE is defined mainly by less clear features of northward-moving rainband. Further analyses indicate that the boreal summer intraseasonal oscillation (BSISO) played a dominant role in affecting the regular/irregular SNM_EASWE during 1961–1979, whereas both the BSISO and the seasonally varying western North Pacific (WNP) eddy may exert notable influences on the regular/irregular SNM_EASWE during 1980–2015 and in the future, where the WNP eddy refers to the anomalous anticyclone/cyclone over the WNP associated with the anomalous western Pacific subtropical high. During 1980–2015, a La Niña-like (El Niño-like) condition in the tropical Pacific during June–July may induce a regular (irregular) SNM_EASWE case because of the influence of anomalous convection over the Maritime Continent on the seasonally varying WNP eddy; an anomalous warming (cooling) in the tropical Indian Ocean during June–July may also partly induce a regular (irregular) SNM_EASWE case via influencing the seasonally varying WNP eddy. The increased influence of seasonally varying WNP eddy on the regular/irregular SNM_EASWE after 1979 are attributed to the increased interannual variability of convective activity over the Maritime Continent and of sea surface temperatures in the Arabian Sea after 1979.

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