西南氣流實驗期間之降水特徵與相關環境型態

Abstract

梅雨期為台灣地區主要雨季之一，在這段時期盛行的西南季風常為位在迎風面的台灣西南部地區帶來豪(大)雨。本研究利用中央氣象局劇烈天氣監測系統(QPESUMS)與台灣電力公司整合閃電偵測系統(TLDS)資料，探討西南氣流實驗期間台灣西南部地區之降水特徵。並利用高時間解析度探空資料進行環境型態特徵之分析。最後討論降水特徵與其相關環境型態間的關聯。 結果顯示，盛行於此期間之降水系統可依據其初生之區域分成三大類：陸生型、海生型以及混合型，其中又以前兩類為主要族群，且兩者個案數發生比率相當，分別有18個和17個。於發展時間上，陸生型主要起始於日間，其發展延時較短。海生型則多於夜間生成，並擁有較長的延時。此外，陸生型多與午後雷雨系統密切相關並有明顯日變化訊息，海生型則無。平均而言，陸生型之降水特徵為系統集中，含較大的對流性降水比率與閃電密度。海生型則常為大範圍的降水並伴隨較大比率的層狀性降水與較小的閃電密度。陸生型多發生於西南氣流較弱的弱綜觀環境下，伴隨有較高的對流可用位能(CAPE)與較低的對流抑制能(CIN)；而海生型則多發展於強盛的西南氣流與較濕潤的大氣條件下，且伴隨著較小的CAPE與較大的CIN。

Mei-Yu season is one of the main rainy seasons in the Taiwan area. The prevailing southwest monsoon flow during this period frequently causes heavy rain events in the windward side of the southwestern Taiwan. In this study, the composited hybrid scan radar reflectivity data of the Central Weather Bureau (CWB)’s Quantitative Precipitation Estimation Segregation Using Multiple Sensors (QPESUMS) system and the lightning data of the Taiwan Power Company (Taipower)’s Total Lightning Detection System (TLDS) were used to examine the precipitation characteristics in southwestern Taiwan during the 2008 Mei-Yu season. In addition, the SoWMEX/ TiMREX field campaign provided high temporal resolution sounding data for documenting the environmental condition. The relations between the precipitation characteristics and their associated environment regimes were explored. A total of 40 rainfall events were identified in the 2008 Mei-Yu season. The results indicate that based on the initiation location, the precipitation events can be classified into three types: land, oceanic, and mixed. The former two types are evenly distributed (18:17) and occupy most of the cases. In terms of the time of development, the land events usually begin in the daytime with shorter durations. In contrast, the oceanic events have their initiations in the nighttime and persist longer. Most of the land events are related to the afternoon thunderstorms and reveal pronounced diurnal cycle signal. In terms of spatial distribution, on the average, the land-type precipitating systems are more concentrated with higher fraction of convective precipitation and higher lightning density while the oceanic types usually consist of widespread area of precipitation associated with larger fraction of stratiform. For the environmental conditions, the land events are associated with larger convective available potential energy (CAPE) and smaller convective inhibition (CIN), whereas the oceanic events are associated with smaller CAPE and higher CIN. Otherwise, the composited soundings show that the oceanic-type has a much stronger and moister southwesterly flow over the lower troposphere than land-type.