2002年梅雨季中正與松山機場低空風切之個案研究

Cases Study on the Low-level Wind Shears at the CKS and Sungshan Airports during the 2002 Mei-yu Season

何台華(Tai-Hwa Hor) ； 涂明聖(Ming-Sheng Tu) ； 蒲金標(Chin-Piao Pu) ； 魏志憲(Chih-Hsien Wei)

《大氣科學》 33卷2期 (2005/06) Pp. 119-142

摘要

本文選擇2002年月14至17日和5月22至24日梅雨季中正及松山機場低空風切警報系統(LLWASS)之風切輸出值、地面自動氣象觀測系統(AWOS)之觀測資料，以及中正及松山機場LLWAS每十秒一筆的測風台原始資料（中正機場有15個測風台，松山機場有13個測風台），藉由速度輻散之三角形遞迴運算所產生的低空風切警報次數、時間分布及風切強度，與此二低空風切警報系統本身所產生的風切輸出值做比對校驗，以瞭解此二低空風切警報系統發出警訊的正確性。更進一步，利用自行運算所產生低空風切的結果分析梅雨季低空風切之發生時機、地形作用，及其與風向、風速和持續時間之關係。
初步研究結果發現：(1)中正機場出現風切的系統輸出值在中度（含）以上風切有高估現象，而松山機場則在強烈風切上有明顯的低估。(2)頻率最高的風切出現在鋒面前緣到達前10分鐘至鋒面前緣到達後20分鐘的30分鐘時距內，對起降中的航機威脅最大。(3)松山機場無論在強盛西南風盛行時期或結構完整的鋒面影響時期，其低空風切皆集中於風向280°～290°間發生，可能跟氣流繞過林口台地、觀音山後經由淡水河口、關渡平原移入台北盆地所導致的管道效應密切相關。在風速方面，除中正機場於西南風盛行時，風速須達到14kt以上才有可能發生低空風切外，其餘情況在風速大於6kt以上，均可能產生有效風切。(4)地形效應延長松山機場的風切持續時間，而且結構完整的鋒面系統影響時，低空風切在此二機場的持續時間均延長。

關鍵字

低空風切 ； 梅雨鋒面 ； 速度輻散 ； 地形效應

並列摘要

In order to realize the accuracy of low-level wind shear alarms at the CKS and Sungshan Airports and investigate the wind-shear-related weather patterns, the topographic effect and the occurrence of the wind shears associated with the wind direction, wind speed, and time duration, the study carefully evaluates the output of the low-level wind shear alert systems (LLWAS) and automated weather observing systems (AWOS). Furthermore, the outcomes of LLWAS are compared with the recalculated results based upon the recursion operation of velocity divergence in use of data collected by the wind towers every 10 seconds which are allocated at the airports (15 wind towers at the CKS Airport and 13 at Sungshan Airport).
The primary findings are: (1) During the Mei-yu season, the product of LLWAS system at the CKS Airport seems over-estimated in the moderate and severe wind shears from the alarm number and wind shear intensity points of view. However, the system output at the Sungshan Airport looks under-estimated in the severe wind shears. (2) The higher frequency of wind shears occurs 10 min prior to the arrival of the Mei-yu frontal system and extends more than 30 min. (3) For the intense southwesterly flow or the well-organized Mei-yu frontal system, the most possible outcome of wind shears occurs between 280 deg and 290 deg in wind direction at the Sungshan Airport, probably due to the channel effect induced by the blocking of Linkou Hill and Guan-yin Mountain. (4) The complicated terrain seems to increase the time interval of wind shears at the Sungshan Airport. Also, the well-organized Mei-yu frontal system is capable to extend the life duration of wind shears at both airports.

並列關鍵字

Low-level Wind Shear ； Mei-yu Frontal System ； Velocity Divergence ； Topographic Effect