Mesoscale Precipitation Patterns in an Occluded Frontal System

囚錮鋒面系統之中範圍降水型態

謝信良(Shinn-Liang Shieh)

《大氣科學》 3卷1期 (1976/05) Pp. 12-27

摘要

本文係分析1973年12月5～7日通過美國華盛頓州之鋒面系統內的中範圍降水特性。利用自動雨量計及雷達資料，發現在鋒面過境期間有六個中範圍雨帶通過觀測網，其中前五個雨帶之寬度相仿，平均約50公里，第六個雨帶的寬度則較其他五個寬一倍。首二個雨帶出現於12月5日，其走向平行於囚錮鋒面系統之暖鋒，次二個雨帶出現於6日，是發生在沿原來冷鋒上新生波動的暖區內，它們的走向似與冷鋒一致，最後二個雨帶是件隨主要冷鋒出現於7日，且與之平行。在雨帶內之較小範圍雨區的集中度由雷達回波上顯示約為每一千平方公里一至三個，平均大小在50至240平方公里之間，此諸回波隨著850－700mb之高空風移動，而雨帶本身之移動方向似與500mb高空風之關係較密切。至於雨區之垂直伸展高度則約為3至7公里。

並列摘要

A case study is presented which illustrates the characteristics and behavior of mesoscale precipitation features associated with an occluded frontal system passing through western Washington State. During the storm period (December 5-7, 1973), six rainbands were observed by means of autographic raingauge and radar data. The first five bands were similar in size, about 50 km in width on average, while the width of the last band was 100 km. The first two bands, observed on December 5, appeared to have been parallel to the warm front of the occluded system. The next two bands, observed on December 6, occurred in the warm sector of a wave which had developed on the cold front and were probably parallel to the cold front. These two bands moved from the southwest at about 35 km h^(-1). The final two bands, observed on December 7, were parallel to the cold front and accompanied its passage. Smaller scale elements, with mean sizes of 50-240 km^2, were embedded in the rainbands in concentrations of 1 to 3 per 1000km^2 and they moved with the wind between 850 and 700 mb (presumably the levels where precipitation particles were generated). The vertical extent of all of the mesoscale rain areas was estimated to be between 3 and 7 km.