東亞地區降水年際變化之研究

嚴偉新(Wei-Sin Yan)

指導教授 ： 曾仁佑

國立中央大學/地球科學學院/大氣物理研究所/碩士(2007年)

摘要

本研究想要探討，在ENSO 事件影響下，東亞地區綜觀尺度擾動之年際變化，以及這些擾動和影響此區的降水特性和動力原因。本研究利用合成的環流場，排除ENSO 以外的作用力，更能了解ENSO 事件時東亞地區環流場的變化過程。
暖事件時上對流層西伯利亞脊減弱，地面西伯利亞高壓跟著減弱，中國大陸下對流層出現壓力負距平。另外上對流層阿拉斯加脊減弱，加上東亞主槽加強，地面阿留申低壓會加強並往東偏移，西太平洋下對流層出現壓力正距平。中國大陸下對流層的低壓距平以及西太平洋下對流層的高壓距平，會為東亞沿岸帶來暖溼的西南風距平。在擾動場中，上對流層的擾動正距平沿著季風路徑往東亞沿岸、東亞主槽往華南延伸以及西太平洋20oN 上方的高壓脊往東偏移，皆有利於東亞沿岸地面的擾動增強，加上暖濕空氣，東亞沿岸降水機會就會增加。
冷事件時，上對流層的東亞主槽會減弱並往西南偏移，西伯利亞脊以及阿拉斯加脊都會增強。下對流層的西伯利亞高壓受到上對流層西伯利亞脊增強的影響，也有增強的現象，中國大陸下對流層出現壓力正距平。受到上對流層東亞主槽以及阿拉斯加脊的影響，下對流層的阿留申低壓減弱，西太平洋下對流層出現壓力負距平。由於中國大陸下對流層的壓力正距平以及西太平洋下對流層的壓力負距平，會為東亞沿岸地面帶來乾冷的東北風距平。在擾動場方面，上對流層的擾動負距平，沿著季風路徑往東南傳播，加上西太平洋20oN 上對流層的高壓脊往西偏移，不利於地面擾動發展。東亞沿岸下對流層擾動減弱，乾冷的東北風增強，東亞沿岸降水的機會減少。

關鍵字

聖嬰/南方震盪

並列摘要

This study investigates the interannual variation of synoptic scale disturbance, and its influence on the characteristic of precipitation. This study utilizes a composite method, which isolates the affect of ENSO, to
understand the evolving process of circulation field in Eastern Asia under theinfluences of ENSO.
In the ENSO warm phase, the Siberian ridge in upper troposphere weakens but the Siberian high in lower troposphere follows to weaken. There is a negative anomaly of surface pressure around the Siberian high area including China. The Alaskan ridge in upper troposphere also weakens but the Eastern Asian main trough in upper troposphere strengthens during the ENSO warm phase, so that the Aleutian low shifts to the east. There is a positive anomaly of pressure in lower troposphere over west Pacific Ocean. In lower troposphere, the negative anomaly of pressure in China and the positive anomaly of pressure in west Pacific Ocean bring warm-wet air into Eastern Asia. On the other hand, a positive anomaly of synoptic scale disturbances in the upper troposphere propagates to Eastern Asia along the monsoon route. At the same time, the ridge over 20oN in upper troposphere in west Pacific Ocean moves to the east. It is advantageous the synoptic scale disturbance to increase in lower troposphere in Eastern Asia. Because of more synoptic scale disturbances and warm-wet air, the precipitation will increase in Eastern Asia.
In the ENSO cold phase, because the Siberian ridge in upper troposphere strengthens, the Siberian high strengthens in lower troposphere. There is a positive anomaly of pressure in lower troposphere around the Siberian high area including China. In upper troposphere at the same time, the Eastern Asian main trough shifts to southwest, and the Alaskan ridge strengthens. Aleutian low in lower troposphere shifts to southwest, so there is a negative anomaly of pressure in lower troposphere in west Pacific Ocean. In lower troposphere, the positive anomaly of pressure in China and the negative anomaly of pressure in west Pacific Ocean bring cold-dry air into Eastern Asia. For disturbance field, the ridge over 20oN in west Pacific in upper troposphere extends to west and it is advantageous the synoptic scale disturbances to decrease in lower troposphere in Eastern Asia. Because of less synoptic scale disturbances and cold-dry air in lower troposphere, the precipitation will decrease in Eastern Asia.

並列關鍵字

ENSO(El Nino / Southern Oscillation)

參考文獻

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