雲對地閃電與降水關係之研究

A Study of the Relationship between Cloud-to-ground Lightning and Precipitation

林熺閔(Shi-Min Lin)

《大氣科學》 27卷1期 (1999/03) Pp. 75-98

摘要

本文首先利用1994～1998年的雲對地閃電資料，分析台灣地區閃電分布的氣候特徵，結果顯示主要閃電大都集中在北部山區及中央山脈西側斜坡，此與陳（1994）的結果大致相同。閃電資料幾乎沒有時間及空間解析度的限制，密集的自動雨量站可以提供每5分鐘降雨量的高時空解析度資料，兩者配合實為研究台灣地區局部對流的寶貴資料。本文選擇五個個案，利用密集的閃電及自動雨量站資料，分析閃電與降雨之間的相關性。結果顯示閃電與對流降水之間有明顯的正相關，午後對流降雨與閃電的相關係數大都在0.7以上，最佳個案可高達0.94。閃電的活躍程度可以作為對流系統強度變化及空間分布的一種指標。本文以5分鐘時間解析度，分析台灣陸地上的閃電與降水發生的時間順序，發現閃電並沒有明顯比降雨早發生，因此本文認為雲對地閃電相對於降雨，應該沒有先導時間（leading time）。高閃電密度的地區必然伴隨強烈對流及降水，但是其間的相關係數及閃電與降水的比值變化很大，不易直接以閃電密度估計降雨量。利用每5分鐘的降雨強度，可以從觀測到的總降雨量中分離出層狀降水與對流降水。正閃電大都集中在整個對流生命期的後三分之二時段內，顯示在對流的成熟期及消散期比較容易發生正閃電。東部地區的閃電密度遠少於西部地區，除了當地對流較少之氣候因素外，現有閃電偵測系統在東部地區的漏失較多也是可能原因之一。

關鍵字

雲對地閃電 ； 先導時間 ； 對流降水 ； 層狀降水

並列摘要

The cloud-to-ground (CG) lightning data from 1994 to 1998 were used to analyze the characteristics of CG lightning distribution over Taiwan area. Most of the CG lightning concentrate over northern mountain area and the western slope of the Central Mountain Rang. The result is similar to that of Chen (1994). Five cases were chosen to investigate the relationship between CG lightning and precipitation. The correlation coefficients of CG lightning and precipitation are above 0.7 for most of the afternoon convection cases, and moreover the best one is over 0.94. The activity of CG lightning can be a good index to describe the temporal and spatial distribution of the convective system. Although the dense CG lightning is closely related to the strong convection as well as precipitation, the correlation coefficients and LR values are quite variable. Therefore, the quantitative estimation of precipitation from CG lightning will be not so easy. The 5 minutes precipitation and CG lightning data were compared to distinguish if the CG lightning occurred before precipitation. The result suggests that there is no obvious leading time of CG lightning to precipitation.A simple method was proposed to separate the convective and stratiform precipitation from the observed precipitation by using 5 minutes rainfall rate. The ratio of positive CG lightning tends to increase during the later life cycle of convective system. It is suggested that the activity of positive CG lightning tends to occur during the mature and dissipation stages. The unusually low amount of CG lightning over the Eastern Taiwan is due to the low efficiency of the current CG lightning detection system over the specific region.

並列關鍵字

Cloud-to-ground Iightning ； Leading time ； Convective precipitation ； Stratiform precipitation