| Summary: | 碩士 === 國立高雄師範大學 === 地理學系 === 102 === This study investigates the circulation patterns of the summer monsoon along with southern Taiwan’s monsoon rainfall. 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. It is found that significantly strong southwesterlies are located over the southern flank of the monsoon trough. For the other type of monsoon pattern, the area north to Taiwan is dominated by a strong westward protruding anticyclone, and a weaker and east-west elongated monsoon trough, which drives the easterly flow to southern Taiwan, is situated south to Taiwan. As the intraseasonal oscillation (ISO) propagates northwestward toward southern China, it will create a favorable environment for the southwesterly flow and convection to develop and become stronger. However due to the latitudinal limit of the northwestward-propagating ISO, the strongest convection over the southern flank of the ISO cyclonic circulation barely reaches southern Taiwan in the westerly phase. Thus, the ISO-westerly pattern seems stronger but brings less rainfall to southern Taiwan. 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. Thus, swithing the low-frequency background flow could have significant impacts on the monsoon rainfall and the associated circulation systems.
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