The Tropical Asian Summer Monsoon Affects Climate Variability Over Yunnan, Southwest China, in May

ABSTRACT It is generally believed that the Asian summer monsoon first establishes in May over the Arabian Sea, Bay of Bengal, Indochina Peninsula and South China Sea, that is, generally with the latitudes lower than 20° N, and these regions are known as the tropical Asian summer monsoon (TASM) region. This study reveals that the climate in May over Yunnan (Latitude ~25° N), Southwest China, where the rainy season starts also in May, shows an interannual variability consistent well with the TASM. On the one hand, the May precipitation and surface air temperature over Yunnan exhibit a significant negative relationship on the interannual timescale, with a correlation coefficient of −0.81, which is one of typical features of TASM during its onset period. On the other hand, this concurrent variability in precipitation and temperature over Yunnan can be well explained by the anomalous circulation related to TASM, which alters the moisture transport into Yunnan. Further analysis suggests that the interannual variability in May climate over Yunnan is affected by the sea surface temperature (SST) anomalies that are similar to the TASM‐related ones, and these SST anomalies appear over the southwest tropical Indian Ocean, in addition to the equatorial central and eastern Pacific previously known. These findings can deepen our understanding of the variability of TASM and have important implications for subseasonal predictions over Yunnan.