近三十年來，對於天氣系統受到阻塞高壓影響而持續的現象，再度引起廣泛討論及研究。許多研究希望找出阻塞高壓發生機制，進而評估其對天氣的預測的助益。北半球的阻塞高壓的氣候特徵是如何？阻塞高壓發生期間有什麼因素造成其暖心結構？阻塞高壓發生時相對渦度與穩定度之間的交互作用是如何？阻塞高壓系統的持續是否有助於臺灣地區滯留性鋒面所造成的降雨？這些問題都值得利用個案的診斷分析來求得解答。 本研究採用了1996年6月至2005年5月共九年的500hPa天氣圖，對北半球持續五天以上的阻塞高壓事件做氣候統計。結果發現，此九年間北半球共有292件阻塞高壓個案，平均每年約有32件；其發生頻率之極大期分別在5、6月(每月佔全年的12%)及12月(每月佔全年的10%)。 為了深入了解阻塞高壓的結構與發展過程，根據九年氣候統計的結果，選取發生於初夏(1998年6月2日至21日)及之初春(2000年3月7日至25日)的兩個東北亞地區阻塞高壓事件做溫度收支與位渦診斷分析。 初春與初夏的兩個阻塞高壓事件，皆幫助了臺灣地區滯留性鋒面的持續，而帶來豐沛的雨量。針對暖心位置，初春阻塞高壓的暖心位置在600hPa以下的中低對流層處，而初夏阻塞高壓的暖心位置則在300-500hPa，約對流層頂。溫度收支的診斷分析結果皆顯示，阻塞高壓暖心結構的增溫主要來自於氣溫的水平暖平流。氣溫的垂直冷平流與絕熱下沉增溫兩者作用相反且互相抵消。由位渦探討穩定度與相對渦度的交互作用，其結果也都顯示了當阻塞高壓增強，穩定度增加，相對渦度減小，位渦減小；當阻塞高壓減弱，則穩定度減少，相對渦度增大，位渦增大。 In recent three decades, scientists discussed widely about the blocking high which may cause the persistence of the weather system. What are the climatic features of the blocking in Northern Hemisphere? For the duration of the blocking, what kinds of factors induce the warm core? And how do the vorticity and the stability interact with each other? In this research, a blocking episode is said to be a closed region and persist more than 5 days. We used weather maps in 500hPa from June 1996 until May 2000 to gather the blocking events. There are 292 blocking episodes (about 32 episodes per year) in the duration. The result shows that the frequency of the blocking has two maximums, May to June and December. In order to realize the structure and the duration of blocking deeply, we chose two cases to diagnose and analyze temperature and potential vorticity. The first blocking event of 20-day duration occurred from 2 through 21 June 1998 over the north eastern Asia. And the other blocking which persists 19 days occurred from 7 through 25 March 2000 over the Northern Pacific and Alaska. The warm core of the first blocking event which occurred during the early summer appears from 300hPa through 500hPa. However, the warm core of the early spring blocking event appears on the lower troposphere where is below 600hPa. From the results of the temperature diagnosis, the horizontal warm advection induces the warm core of the blocking. In the vertical motion, the vertical cold advection and the adiabatic warming are contrary. Subsequently, the result of the potential vorticity reveals that as the blocking enhances, the stability increases and the resolute vorticity decreases.
