西太平洋地區颱風季季內振盪年際變化之研究

Interannual Variations of the Intraseasonal Oscillation during Typhoon Season over Western Pacific

徐邦琪(Pang-Chi Hsu) ； 鄒治華(Chih-Hua Tsou) ； 柯文雄(Wen-Shung Kau) ； 許晃雄(Huang-Hsiung Hsu)

《大氣科學》 33卷1期 (2005/03) Pp. 29-48

摘要

季內振盪與熱帶地區短期氣候變化密切相關，本篇研究主要目的即在探討西太平洋季內振盪年際變化與熱帶風暴活動、中東太平洋海溫的關連性。研究結果顯示，西太平洋地區不僅為颱風季七-九月氣候平均之降水變異量極值區，降水及季內振盪的年際變化在此區均十分顯著。本文將西太平洋(120°-180°E，0°-30°N)等距離區分為四個區域，進一步探討西太平洋各區域季內振盪與熱帶風暴生成數目的年際變化。在西太平洋東南區域(150°-180°E，0°-15°N)，當東太平洋七-九月海溫較高（低）時，30-60天及10-20天季內振盪均較活躍（不活躍）。在東南區域，30-60天OLR變異量與熱帶風暴生成數目呈高度正相關。西北區域(150°-180°E，15°-30°N)季內振盪的年際變化與東太平洋海溫之關係較為複雜，且熱帶風暴生成數目與季內振盪變異量並無顯著的相關性存在。
當東太平洋海溫較暖時，西太平洋暖水區向東南伸展，沃克環流上升區、低層輻合區及季風槽亦具有東/東南發展的特徵。同時，暖年時，30-60天西風、南風和正渦度均比冷年時活躍。因此，在東太平洋海溫較高時，30-60天季內振盪與平均環流熱力場和動力場上之正回饋作用為西太平洋東南區域提供一有利熱帶風暴生成的環境，使東南區域有較多熱帶風暴生成。

關鍵字

季內振盪 ； 熱帶風暴 ； 年際變化

並列摘要

Intraseasonal oscillation (ISO) is closely related to the short-term climate variability in the Tropics. This study attempts to investigate the relationship among the interannual variabilities of ISO, activities of tropical storms and sea surface temperature over Eastern-Central Pacific. The results show that the maximum variance of climatology precipitation during typhoon season (July to September) is located in the Western Pacific. In addition, interannual variations of the precipitation and the ISO are also significant in the Western Pacific. To investigate the interannual variabilities of ISO and tropical storms in this region, we divided the Western Pacific (120°-180°E, 0°-30°N) into four sub-domains. In southeast domain of Western Pacific (150°-180°E, 0°-15°N), the 30-60 day and 10-20 day oscillation are more (less) active than climatology when Nino3.4 SST is warm (cold) during typhoon season. Moreover, 30-60 day ISO intensity in this domain is highly correlated with the numbers of TS formations. However, the relationship between interannual variations of ISO in northwest domain (120°-150°E, 15°-30°N) and Nino 3.4 SST is complicated. The numbers of TS formation has no relations with the ISO intensity in northwest domain.
During Nino3.4 SST warm years, the warm SST over Western Pacific, the rising branch of Walker circulation, the area of low level convergence and monsoon trough all extend south/southeastward. In addition, 30-60 day westerlies, southerlies and cyclonic vorticity also enhance and extend south/southeastward. This positive feedback between monsoon mean flow circulation and 30-60 day oscillation are favorable for the formation of TS in the southeast domain of Western Pacific.

並列關鍵字

Intraseasonal oscillation ； Tropical storm ； Interannual variability