Weakening of the Winter Monsoon and Abrupt Increase of Winter Rainfalls over Northern Taiwan and Southern China in the Early 1980s

Chih-wen Hung Department of Geography, National Taiwan Normal University, Taipei, Taiwan

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Pei-ken Kao Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan

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Abstract

The rainfall characteristic of the East Asian winter monsoon (EAWM) is less emphasized in previous works. This study reveals that the circulation of the EAWM weakened in recent decades, which results in a decrease of winter rainfall over several windward coastal areas over East Asia including the hills in northern Taiwan. In contrast, there is an abrupt increase of rainfall in southern China and the plains of northern Taiwan during the early 1980s. This is due to the increase in sea surface temperature and lower-troposphere moisture over the South China Sea and the anomalous northward flow that enhances the moisture transport to southern China. Because more moisture is provided for the frontal system that moves eastward, the fronts frequently come with abundant moisture and a well-developed rainband in winter. Therefore, the plains of northern Taiwan receive more rainfall after the 1980s.

Corresponding author address: Dr. Chih-wen Hung, Department of Geography, National Taiwan Normal University 162, Sec. 1, Hoping East Rd. 106 Taipei, Taiwan. Email: cwhung@ntnu.edu.tw

Abstract

The rainfall characteristic of the East Asian winter monsoon (EAWM) is less emphasized in previous works. This study reveals that the circulation of the EAWM weakened in recent decades, which results in a decrease of winter rainfall over several windward coastal areas over East Asia including the hills in northern Taiwan. In contrast, there is an abrupt increase of rainfall in southern China and the plains of northern Taiwan during the early 1980s. This is due to the increase in sea surface temperature and lower-troposphere moisture over the South China Sea and the anomalous northward flow that enhances the moisture transport to southern China. Because more moisture is provided for the frontal system that moves eastward, the fronts frequently come with abundant moisture and a well-developed rainband in winter. Therefore, the plains of northern Taiwan receive more rainfall after the 1980s.

Corresponding author address: Dr. Chih-wen Hung, Department of Geography, National Taiwan Normal University 162, Sec. 1, Hoping East Rd. 106 Taipei, Taiwan. Email: cwhung@ntnu.edu.tw

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