UAW2009：ENSO對臺灣冬季季風之影響

The impact of the ENSO on the winter monsoon in Taiwan

The East Asian region is influenced by the large low-level cyclonic and anticyclonic Asian monsoon circulation in summer and winter seasons, respectively. For most of the Asian monsoon regions such as South Asia, the summer monsoon season is referred to the “rainy season”, while the winter is usually a dry season. Over East Asia, there is a similar wet/dry and warm/cold monsoonal characteristics for the summer/winter season. However, the influence of the monsoon circulation in Taiwan is not exactly the same as this traditional point of view.

In northern Taiwan, the northerly and northeasterly flow of the East Asian winter monsoon (hereafter EAWM) can produce the orographic rain along the coastal regions during winter. In addition to this effect, the frontal activity is another source of rainfall for northern Taiwan during winter. Therefore, the wet/dry monsoonal characteristic is not fully applied in northern Taiwan. However, in southern Taiwan, this wet/dry monsoonal characteristic is clear. The major rainy season over there is during summer and the winter season is usually dry.

In addition to the monsoonal rainfall characteristic, the “Fall Wind” in the southernmost region of Taiwan, Hengchun, is another important phenomenon. The local “Fall Wind” is strong in the Hengchun region due to the northeasterly flow of the EAWM which can cross the lower central mountain range in the southernmost region of Taiwan. In the present study, it is found that the occurrence of the “Fall Wind” has significant interannual variations related to the ENSO signals. During the La Nina / El Nino phase, the cold/warm sea surface temperature anomalies over the equatorial Eastern Pacific can produce the cyclonic/anticyclonic anomalous circulations over the Philippine Sea which enhance/weaken the northeasterly wind in adjacent to Taiwan. As a consequence, more/less Fall Wind days observed in the Hengchun area is found.

UAW今年將在韓國首爾召開。
http://ces.snu.ac.kr/uaw09/index.htm