Influence of 30–60 Days Intraseasonal Oscillation of East Asian Summer Monsoon on Precipitation in Southwest China

Abstract

The intraseasonal oscillation (ISO) of the East Asian summer monsoon (EASM) is an important factor affecting summer precipitation in China, but the relationship between the ISO of the EASM and summer precipitation in southwest China is currently still unclear. The relationship between the two is discussed, and the following conclusions are drawn: (1) there is a significant positive correlation between East Asian monsoon surge intensity and summer precipitation in southwest China. When the monsoon surge is stronger (weaker), the precipitation in southwest China is more (less). However, the areas where the monsoon surge has a more obvious effect on the summer precipitation in southwest China are mainly located east of 105° E, and the monsoon surge has no obvious effect on the area west of 105° E. This may be more (less) the case in monsoon surge years, when a low-frequency oscillation of 30–60 days (10–20 days) plays a dominant role. The East Asian region has a longitudinal wave train of “+ − +” (“− + −“), the western Pacific subtropical high is westerly (easterly), the South China Sea and western Pacific is affected by anticyclone (cyclone), the EASM is active (suppressive), eastern southwest China has water vapor convergence (divergence) and upward (downward) airflow. (2) We found that 1998 was a typical year for the 30–60 days ISO of the EASM. There are two obvious 30–60 days oscillation cycles. In this year, when the intensity of the ISO of the EASM increases (decreases), the range of positive precipitation anomaly region in southwest China extends (decreases). The atmospheric circulation characteristics show that, when the western Pacific subtropical high is west (east) and south (north), and there is obvious anticyclonic (cyclonic) circulation in China–western Pacific, and the EASM is stronger (weaker), which leads to more (less) precipitation in southwest China.