台灣地區夏季乾旱之監視與預報（一）：多雨年與少雨年的氣象條件

On the Monitoring and Prediction of the Summer Drought in Taiwan Area (I): Meteorological Conditions in the Abundant and Deficit Rainfall Years

吳明進(Ming-Chin Wu)

《大氣科學》 20卷1期 (1992/03) Pp. 35-46

摘要

分析台灣地區夏季七、八、九月，各地降水的特徵，探討台灣地區夏季乾旱的特性，分析各月降水、和El Nino。颱風發生數、登陸數、以及北半球500毫巴環流與太平洋海面溫度間的關係，來探討夏季乾旱的成因，作台灣地區夏季乾旱之監視。找出其領先因子，作為乾旱長期預報的參考。結果發現台灣地區夏季的降水常具有相當強度，大部份和颱風有關，在空間上有相當的一致性，在時間上則相關較不明顯。八月和九月的降水量有相反的趨勢。七月降水在El Nino年增加。七、八、九月的降水皆和北半球500毫巴的副熱帶高壓的強度及位置有關。七月的乾年副高較強且延伸到中國大陸東南。八月的乾年太平洋副高向東退縮。亞洲南邊的高壓脊往東延伸，籠罩台灣地區。九月的乾年副熱帶高壓偏東而正距平籠罩台灣地區。七、八、九月的降水也和熱帶太平洋的海面溫度的分佈成明顯的關係，七月和八月的乾年，西北太平洋海面溫度較高，東太平洋海面溫度則較低，九月乾年的情形則相反。可能的原因為西北太平洋海面的高溫加強熱帶的對流活動，因而改變副熱帶高壓的強度及位置，而分別造成台灣地區七月和八月的少雨和九月的多雨。由於海面溫度有相當的延續性，故熱帶太平洋的海面溫度，可能成為台灣區夏季乾旱預報的一領先指標。

關鍵字

夏季乾旱 ； 颱風 ； 副熱帶高壓 ； 熱帶太平洋海面溫度

並列摘要

In order to investigate the formation mechanisms of the summer drought in Taiwan area, we examine the station summer rainfall in July, August and September over Taiwan area to study the characteristics of the summer drought in Taiwan area. We also study the relationships of the rainfall in the specific month with El Nino, number of Typhoon formation, number of Typhoon invasion, and 500mb circulation in the Northern hemisphere as well as the sea surface temperature over the tropical Pacific ocean. It is intended to monitor the summer drought and find out the leading factors for the summer drought long range forecasting. The results indicate that the summer rainfall always showes strong intensity, and most of these heavy rainfall days is related to typhoon. The precipitation is quite homogeneously distributed in the spatial, but is relatively incorrelated distributed in the monthes. The August & September precipitation are tended to be reverse. July rainfall increased in the El Nino year. July, August & September rainfall are all closely related to the intensity and position of the 500mb northern hemispheric subtropical high. In the dry July, the subtropical high tend to be stronger and extend to the Southest China mainland. In the dry August, the subtropical high tend to retreat to the east. The ridge over the Southern Asia extended to the east and cover Taiwan area. In the dry September, subtropical high tend to be weaker, but the positive anomaly cover Taiwan area. Precipitation in July, August and September are also quite closely related to the distribution of the sea surface temperature in the tropical Pacific Ocean. In the dry July and dry august years, sea surface temperature over the Northwestern Pacific Ocean tend to be high, while sea surface temperature is lower over the Eastern tropical Pacific Ocean. This jadaposition of the sea surface temperature is reversed in the dry September year. The plausible cause could be that the high sea surface temperature over the Northwestern tropical Pacific inhense more tropical deep convection activity and hense change the intensity and position of the northern Pacific subtropical high. This change herald a dry July and August as well as wet September in Taiwan area. Due to the relatively persistency of the sea surface temperature, the sea surface temperature over the tropical Pacific Ocean could be a plausible leading index of the summer drought in Taiwan area.

並列關鍵字

Summer Drought ； Typhoon ； Subtropicalhigh ； Tropical Pacific Ocean SST