台灣海峽北部與鄰近地區春夏中尺度對流系統之氣候特徵

Climatological Characteristics of the Mesoscale Convective Systems over the Northern Taiwan Strait and the Adjacent Areas in Spring and Summer

陳泰然(George T. J. Chen) ； 周鴻祺(H. C. Chou) ； 林宗嵩(T. S. Lin) ； 楊進賢(J. S. Yang)

《大氣科學》 24卷3-4期 (1996/12) Pp. 145-163

摘要

本文利用民航局中正機場雷達回波資料，分析1988-1993年2-7月台灣海峽北部及鄰近地區中尺度對流系統之氣候特徵。除分析個案特徵外，亦分析所有線狀對流系統及不同走向系統在不同生命階段之空間分佈。此外，探討中尺度對流系統發生頻率之年際變化、季節分佈及日夜變化，並依線狀對流形成型態、層狀降水區型態及綜觀型態，進行不同類別之分析與頻率分佈，最後分析線狀對流生命期。結果顯示，各年與各月出現之非線狀對流系統均較線狀者為多。不論線狀或非線狀對流系統之回波開始出現時間或形成期出現時間，均無明顯日夜變化。但線狀與非線狀系統發生頻率均有顯著季節變化，並以5月最多；平均移速均亦有顯著季節變化，以4月最快，且後者較前者為快。線狀對流主要發生在海峽北部及台灣西北部沿海一帶，於台灣西北部沿海進入成熟期，並於北部地區與東北部沿海消散。線狀對流形成型態以後造型最多，破線型次之，前造型與破面型最少。鋒面雲帶之線狀對流，以發生於地面鋒後者最多，發生於鋒上與鋒前者相近。線狀對流主軸與鋒面走向，以平行者最多，交角在20°-60°者次之，垂直者最少。此外發現，線狀下流平均生命期為7.6小時，於5-6月梅雨季較長，3-4月較短。不同形成型態系統之生命期。以破面型10小時最長，破線型7.3小時最短。形成期至成熟型與成熟期至消散期之平均時間相近，各為2.1小時。形成期至消散期之平均時間為4.2小時，以破面型6.1小時最長，後造型與前造型之4.1小時最短。

關鍵字

線狀對流 ； 年際變化 ； 季節變化 ； 形成形態 ； 生命期

並列摘要

The main purpose of this paper is to investigate the climatological characteristics of mesoscale convective systems (MCSs) over the northern Taiwan Strait and the adjacent areas in February-July 1988-1993 using the radar reflectivity data as observed by CKS Airport Doppler radar. In addition to the general features of each individual cases, analyses were carries out to reveal the spatial distribution of various types of line convection at different life stages. Frequency distribution was analyzed to reveal the interannual, seasonal, and diurnal variations. The general characteristics are presented for various types of line convection, including different types of formation, stratiform region, and synoptic conditions. The life span of various types were also analyzed.Results showed that the line convection type occurred less frequently than the non-line convection type in each month and each year analyzed. No diurnal variations existed in the temporal frequency distribution of the time of the first echo appearance and the formation stage for both types. However, there was a clear seasonal change in frequency with maximum occurring in May. A clear seasonal change in the mean propagation speed also existed with a maximum occurring in April. In general, non-line convection moved faster than line convection. Line convection mainly formed over the northern Taiwan Strait and coastal area of northwestern Taiwan, reached mature stage over northwestern coastal area, and dissipated over northern Taiwan and northeastern coastal area. Frequency distribution for the different formation types of line convection showed a maximum for backward building type, followed by broken line type, and a minimum for forward building and broken areal types. The line convection associated with the frontal cloud band occurred most frequently to the north of surface front and followed by that occurred along and ahead of front. Line convection occurred most frequently with an axis parallel to the front, followed by that oriented with an angle of 20°-60° to the front, and then with an axis perpendicular to the front.Results also showed that the mean life span of line convection was 7.6 h with a longer duration in the Mei-Yu season of May-June and a shorter duration in March-April. Broken areal type had a longest duration of 10 h and broken line type had a shortest duration of 7.3 h. The mean duration of 2.1 h from formation stage to mature stage was about equal to the from mature stage to dissipation stage. The mean duration from formation state to dissipation stage was a maximum for broken areal (6.1 h) and a minimum for both backward building and forward building types (4.1 h).

並列關鍵字

line convection ； interannual variation ； seasonal variation ； formation pattern ； life period