Mesoscale ensemble experiments on potential parameters for tornado outbreak

Abstract

Energy Helicity Index (EHI), defined by the product of Convective Available Potential Energy (CAPE) and Storm Relative Environmental Helicity (SREH), is one of potential parameters to diagnose the possibility of tornado outbreak. In this study, probabilities that EHI exceed some criteria were examined with a mesoscale ensemble prediction system, whose grid interval was 15 km, in two tornado events in Japan (Nobeoka and Saroma tornado events). High probability regions (HPR, hereafter) of large SREH existed in the northeastern quadrants of a typhoon or a low-pressure system, while HPRs of large CAPE extended along the warm humid airflow from the Pacific Ocean. In the two events, the tornados were formed near HPRs of large EHI, where HPRs of large SREH and CAPE were overlapped. This result indicates the possibility of the probability forecast of the potential parameter for tornado outbreak. ©2009, The Meteorological Society of Japan.