An Instability Index for Lightning Prediction in Typhoon

Abstract

In this paper, we analyze the equivalent potential temperature (EPT) at lightning locations in typhoons in order to determine whether a storm in typhoon produces lightning. We examined the vertical profiles of EPT and found that the lightning producing thunderstorm in typhoon typically had two instability layers at upper level (250hPa-300hPa) and lower levels (600hPa-700hPa), while the normal thunderstorm usually has single instability layer. The difference between the 250hPa EPT and 300hPa EPT in the upper-level convective instability is used to create an instability index for the forecast of lightning flashes particularly in typhoon. We calculated the False Alarm Rate (FAR), the Probability of Detection (POD) and the Critical Success Index (CSI) for the lightning prediction in typhoons with the value of 250hPa EPT and 300hPa EPT. As a result of the statistical analysis, when the 250hPa EPT of 367K or more and 300hPa EPT of 390K or less, the POD and FAR showed the highest score of 0.66±0.38 and 0.35±0.14, respectively. In this condition, CSI showed the highest score of 0.45±0.26. The proposed that N-index, namely the 250hPa EPT of 367K or more and 300hPa EPT of 390K or less, can be used as a specialized index for the prediction of lightning in typhoon.