雲對地閃電和雷達回波參數之相關：個案研究

The Cloud-to-Ground Lightning Related to the Reflectivity Parameters: Case Study

洪景山(Jing-Shan Hong)

《大氣科學》 30卷1期 (2002/03) Pp. 21-34

摘要

本研究是針對1999年8月27至29日連續三日發生於北部山區之午後對流個案，分析其所伴隨之雲對地閃電行為以及探討閃電活動和雷達回波參數之相關。分析結果顯示三個個案中正閃電和負閃電的比率分別為13.82％、13.25％和2.53％，最大的閃電頻率分別為64、72以及83(6min)^(-1)。個案中閃電的空間分佈範圍和大回波中心所在的位置一致，這意味著閃電活動和對流發展的強度有密切的關係。閃電頻率隨時間的變化和10～40 dBZ回波頂高度並沒有太大的相關，而和50 dBZ之回波頂高度較有關係。然而閃電頻率的峰值和回波頂高度之間並沒有顯著的對應關係，反倒是和最大垂直液態水總含量(vertical integrated liquid, VIL)有較好的相關，二者相關係數可達0.8以上。
當閃電頻率增加時，大部分的閃電均發生在大回波區中。閃電位置所在的3公里高度回波強度在40～50 dBZ之間有一個閃電總量的峰值，但是在小於10 dBZ的回波範圍中亦有一個閃電總量的峰值，而此一閃電頻率峰值主要是發生在回波為40～50 dBZ之閃電頻率峰值剛開始建立之時。此外，大部分閃電發生位置所在的VIL值均在10 Kg m^(-2)以下，但是當閃電頻率增加，特別是閃電頻率達到峰值時，閃電發生的位置不僅在大的VIL區間（大於15 Kg m^(-2)）有增加的趨勢，在較小的VIL區間也有增加的趨勢。這有可能是：1、大VIL區域或大回波區域和強上衝流的所在不一致；2、電荷分佈可能受水平平流作用而離開強上衝流的所在的位置，因此在小VIL區域亦有大的閃電頻率出現。

關鍵字

云對地閃電 ； 回波頂高度 ； 垂直液態水總含量

並列摘要

The cloud-to-ground lightning (CG) behavior and its relations to the reflectivity parameters were studied for the afternoon thunderstorm cases occurred during 27-29 August 1999.The results showed that the maximum CG flash rate were 64, 72,and 83(6 min)^(-1) and the percentage of the positive to the negative CG counts were 13.82%, 13.25%, and 2.53%, respectively. The time series of the CG flash rate were close related to the maximum echo top of 50 dBZ. However, The relation between the peak of the CG flash rate and the echo top were not clear, but well indicated by the maximum vertical integrated liquid (VIL) derived from the reflectivity.
Most of the CG lightning was occurred around the large reflectivity area as the CG flash rate increased. The analysis of the statistics for the 3-km reflectivity at the CG locations showed that there were two peaks were found for 40～50 and less 10 dBZ range. Most of the CG lightning were occurred where the VIL were less than 10 Kg m^(-2). However, as the CG flash rate increased, the more CG lightning was occurred at the area with larger VIL(＞15 Kg m^(-2)).The results implied that the closed relations between the CG lightning activities and the hails in the convective systems.

並列關鍵字

Cloud-to-ground lightning ； Echo top ； Vertical integrated liquid