Enhanced connections between summer precipitation over the Three-River-Source region of China and the global climate system

Abstract

This study reveals an enhanced correlation between the interannual variability of summer precipitation over the Three-River-Source (TRS) region of China and North Atlantic Oscillation (NAO), western Indian Ocean sea surface temperature (SST), El Nino-Southern Oscillation (ENSO), and the East Asian summer monsoon (EASM) for past decades, revealing an enhanced connection between the summer climate of the TRS region and the global climate system. Underlying causes are investigated based on a comparison on the climate effects associated with the aforementioned factors between periods 1961–1980 and 1991–2014. Enhanced connections to NAO are mainly attributed to the fact that the increased atmospheric moisture over the Arctic region has an enhanced latent heating on convective activity over the Hudson Bay-Davis Strait region under negative-phase NAO, generating an intensified anomalous high over Greenland and further stimulating an Eurasian wave-train influencing the TRS region. Similarly, for an El-Nino decaying summer, convection anomalies over the Maritime Continent are more significant due to enhanced latent heating observed in 1991–2014, which in turn have a more significant influence on the summer climate in TRS region. Regarding western Indian Ocean SSTs, warming in the western Indian Ocean is characterized by a warming center north (south) of the equator for 1991–2014 (1961–1980); correspondingly, the associated Kelvin wave-induced Ekman divergence mechanism is more pronounced over the Bay of Bengal and South China Sea for 1991–2014. Enhanced connections to the EASM are mainly attributable to a combined effect of Indian Ocean warming and anomalous convective activity over the Maritime Continent associated with ENSO.