臺灣地區冬季鋒面系統之天氣特徵研究

Characteristics of Frontal Systems Over Taiwan Area in Winter

陳泰然(George Tai-Jen Chen) ； 廖珮娟(Pei-Chuan Liao)

《大氣科學》 39卷2期 (2011/06) Pp. 147-175

摘要

本研究分析1994年11月至2002年2月之冬季月份（11、12、1、2月）影響臺灣地區具有顯著鋒面特徵的冷鋒個案，發現均屬上滑鋒。再依據鋒面南側垂直於鋒面水平風場之差異特徵，將上滑鋒區分為暖型與冷型上滑鋒，探討其對臺灣地區天氣之影響。結果發現：暖型上滑鋒臺灣地區鋒前受太平洋高壓脊西伸至臺灣鄰近海面影響，鋒前近地層風場為南風分量所主宰，鋒後受大陸高壓影響，為北風分量主宰。冷型上滑鋒臺灣地區受大陸冷高壓影響，鋒前鋒後均為北風分量，唯鋒後北風分量較大。
鋒面溫度距平變化與混合比之南北差異分析顯示，冷型上滑鋒鋒後冷乾空氣南移之變性程度較暖型者為弱，溫度距平傾向則顯示冷型上滑鋒有較暖型者為強的鋒面斜壓性。氣壓距平傾向之南北變化顯示，暖型上滑鋒愈往南移動冷空氣愈淺薄，而冷型上滑鋒並無此特徵。
雨量分布顯示，暖型上滑鋒過境因迎風面地形效應致使東北部於鋒後有最大降雨強度，而東南部於鋒面過境前後出現最大降雨強度，可能原因為鋒面過境前有較強南風與較大混合比之故。冷型上滑鋒過境西部與東部地區均有鋒前降雨強度往南減小之趨勢，鋒後東部地區較西部地區為大之降雨強度亦反映迎風面之地形效應。

關鍵字

冷鋒 ； 上滑鋒 ； 下滑鋒 ； 暖型上滑鋒 ； 冷型上滑鋒

並列摘要

The characteristics of frontal systems in the Taiwan area during the winter of 1994-2002 (Nov.-Feb.) were investigated in this study. Thirteen representative anafronts were identified. These cases were classified into warm-type and cold-type anafronts according to their horizontal wind field distribution in the area to the south of the fronts in the lower troposphere. During this period, no katafront was identified. The domination of anafronts was probably due to the fact that the angle between 700 hPa flow and the surface front was so small in the subtropics that the surface front usually moved faster than the wind speed at the upper levels, resulting in a relative upslope motion of warm air along frontal interface.
The southerlies prevailed in the prefrontal areas of warm-type anafronts during the period of the dominance of the subtropical ridge, while the northerlies prevailed in the prefrontal areas of cold-type ones during the period of the dominance of the Mongolia high.
Significant precipitation occurred over northern and northeastern Taiwan during the passage of both types of anafronts, whereas it was larger in the cold-type than that in the warm-type. For the warm-type, significant rainfall also occurred over southeastern Taiwan because of the orographic lifting of the warmer and moister southerlies. The temperature decreased faster over western Taiwan than that over eastern Taiwan, and the decreasing rates of temperature of the cold-type were larger than those of the warm-type; the pressure increased faster over western Taiwan than that over eastern Taiwan, and the increasing rates of pressure of the cold-type were larger than those of the warm-type. The southerlies changed to northerlies during the passage of the warm-type anafronts, whereas the northerlies prevailed during the passage of cold-type ones. Before the frontal passage, the mixing ratio of the warm-type was larger than that of the cold-type.

並列關鍵字

cold front ； anafront ； katafront ； warm-type anafront ； cold-type anafront