Interannual Variations of Tropical Upper Tropospheric Divergence and Pacific Teleconnections During Northern Winter

冬季熱帶對流層高空輻散場之年際變化與太平洋區之遙相關

張智北(C.-P. Chang) ； M. S. Peng ； J. S. Boyle

《Terrestrial, Atmospheric and Oceanic Sciences》 1卷4期 (1990/12) Pp. 337-362

摘要

本文採用美國海軍十五年間(1974～1988)熱帶分析資料以研究太平洋區冬季200毫巴氣流之年際變化。與一般作業資料不同，此資料之輻散場不受數值模式預報之影響，同時此資料亦與平均時間長波輻射資料較相近。資料分析結果顯示赤道區有兩主要之大尺度輻散距平中心，其一位於太平洋之中部另一位於西太平洋印尼、菠蘿洲一帶，而此二輻散距平則呈反相之變化。第三個主要之輻散距平中心在墨西哥西岸之西南方，此距平中心亦和太平洋中部之距平中心亦呈異相之變化。
由複合或單點相關計算結果皆顯示遙應型態和赤道區輻散距平間有重要之相互關係，尤其是太平洋中部之輻散是促成PNA型態之重要外力，而印尼、菠蘿洲一帶之輻散則是促成北太平洋東北向波群型態之主要外力。這兩種遙相關型態在東北太平洋之流線函數距平互成異號。
我們進一步將輻散基點沿著赤道帶移動觀看相關係數值改變之情形，由此計算之結果顯示有些由環流模式模擬結果所得“遙相關型態隨熱帶外力位置改變並不敏感”之說法只在相當有限之範圍内才正確，在太平洋熱帶區如赤道之輻散基點在150°E和120°W間移動時PMA相關型態只做小輻度之政變，但將基點移出比範圍時，相關型態會有非常明顯的改變。

並列摘要

A 15-year(1974-1988)data set based on the US Navy's tropical global band analysis is used to study the interannual variations of 200mb winter flow over the Pacific. The divergence fields are free from numerical model prediction influences that typically exist in operational data sets, and agree well with the mean outgoing longwave radiation data. An out-of-phase variation between two major equatorial centers of large-scale divergence anomalies, one over the central Pacific and the other over the western extreme of the western Pacific (maritime continent), is most noticeable. A third major center of divergence anomalies is located southwest of the Mexican coast. This center also shows an out-of-phase variation with that in the equatorial central Pacific. Composite and single-point correlation studies support the notion that the teleconnection patterns are related to equatorial divergence anomalies. In particular, divergence forcing from the central Pacific appears important for the PNA pattern, and forcing from the maritime continent area appears important for a northeastward wave train pattern in the North Pacific. These two teleconnection patterns have streamfunction anomalies of the opposite sign over the northeastern Pacific. By examining the change of correlation patterns as the divergence base point is moved around the equatorial belt, the insensitivity of the teleconnection pattern with respect to tropical forcing locations as reported by several general circulation model simulations is observed only within limited regions. In the equatorial Pacific, the PNA correlation pattern changes slowly when the equatorial divergence base point is within150°E-120°W.The pattern changes rapidly when the base point is moved outside of this region.