Characteristics of Summertime Circulation Patterns for Southern Taiwan’s Monsoon Rainfall from July to September

Abstract

This study documents the circulation features associated with summer monsoon rainfall over southern Taiwan from July through September over the period 1974 -2001. Four types of monsoon systems, Monsoon I, I-TC, II and II-TC, are identified based on the daily rainfall data of 4 observational stations over southern Taiwan and the daily wind direction data of Lanyu. The total rainfall amount of Monsoon I and I-TC is much greater than that for Monsoon II and II-TC because the former two have more moisture. Monsoon I is characterized by a strong southwesterly flow over southern Taiwan due to the tightening of the pressure gradient between the monsoon trough and subtropical high over the western North Pacific. The Monsoon I-TC pattern exhibits a deep monsoon trough along with an anomalous cyclone near the East China Sea; this pattern drives a large volume of moisture that causes heavy rainfall over southern Taiwan. The circulation patterns of Monsoon I and I-TC resemble the flow pattern during the Mei-Yu or "Plum Rain" season from May through mid-July. The Monsoon II pattern reveals a trough south of Taiwan and accompanied by a strong ridge north to it. The convection is located near the southern flank of the monsoon trough. The circulation pattern of Monsoon II-TC yields a deep trough south of the westward protruding subtropical ridge. Additionally, the Monsoon II-TC is less significant because of the wide variety of the TC locations. The Monsoon II and II-TC patterns are similar to the Pacific-Japan (PJ) pattern that can affect weather in the East Asian summer monsoon area.

Initiation and Maintenance Mechanisms for Heavy Precipitation System over a Mountainous Island under a Prevailing Monsoon Current

“…The northerly wind associated with Wukong's outer circulation over southeastern China coast converged with westerly wind over southern Taiwan Strait and northeastern SCS. The flow pattern is similar to Monsoon I-TC type proposed by Ko & Tzeng (2013). The westerly wind was about 3 ms -1 , which gave a low F w~0 .15.…”

“…Meanwhile, the western Pacific high pressure extended to The Philippines resulting in southwesterly flow over northern SCS, Taiwan Strait, and Taiwan. The flow pattern is similar to Monsoon I type proposed by Ko & Tzeng (2013). The low-level prevailing southwesterly wind speed was about 8.8 m s -1 and the F w is about 0.3 (h~2500 m and N w~0 .01 s -1…”

ISO-Modulating Effects on the East Asian Summer Monsoon Circulation Patterns Associated with Southern Taiwan’s Monsoon Rainfall

“…To isolate the intraseasonal signals, the Butterworth bandpassed filter (Kaylor 1977), which was employed by Hsu and Weng (2001), Ko andHsu (2006, 2009), and Ko et al (2012), was applied in this study to extract the 30-80-day (intraseasonal) fluctuations.…”

“…Ko and Hsu (2009) examined the effect of ISO modulation on submonthly wave patterns (Ko and Hsu 2006) propagating north-northwestward from the northeast of Papua New Guinea to the oceanic area between Taiwan and Japan. They reported that when the ISO cyclonic circulation propagated northwestward (Wang and Rui 1990;Hsu and Weng 2001;Tsou et al 2005), the submonthly wave pattern during the ISO westerly phase was better organized in the cyclonic and moistureconverging environment of a strong eastward-extending monsoon trough.…”

Relationship between the Interannual Variations of Summer Convective Afternoon Rainfall Activity in Taiwan and SSTA(Niño3.4) during 1961–2012: Characteristics and Mechanisms

“…26 also indicated that the changes of the SSTA in the tropical Pacific and the Indian Ocean impact the changes of the WNPSH. Because the changes in the EASM circulation, moisture transport and WNPSH are the most important factors that affect the CAR formation in Taiwan 10,27,28 , we then hypothesize based on these documented studies that (1) there might be a close relationship between the interannual variation of CAR activity in Taiwan and SSTA over the tropical Pacific regions, and (2) this relationship might have changed after the 1990s. These two hypotheses will be examined herein.…”