Relationship between the ISO and the East Asian summer monsoon circulation patterns

This study analyzes the links between the intraseasonal oscillation (ISO) and the summer monsoon circulation patterns. Two types of monsoon patterns are defined: one is characterized by a broad low pressure area extending from a low pressure center near southern China northeastward toward southern Japan. Significantly strong southwesterlies are found over the southern flank of the monsoon trough. For the other type of monsoon pattern, the area north to Taiwan is occupied by a strong westward protruding anticyclone, and a weaker and east-west elongated monsoon trough, which drives the easterly flow to southern Taiwan, is located south to Taiwan. The ISO tends to modulate the monsoon flow patterns as the ISO propagates northwestward toward southern China, creating a favorable environment for the southwesterly flow to become stronger. Therefore, the ISO-westerly pattern seems stronger than that in the easterly phase. The ISO tends to generate anomalous cyclone/anticyclone that could affect the southwesterlies and northeasterlies near its northern and southern rims through tightening the pressure gradients.