Relationships between Updraft Characteristics and Cloud-to-Ground Lightning Activity in Warm-Season Convective Storms in the Kanto Region, Japan

This study investigated two aspects of the relationship between cloud-to-ground (CG) lightning activity and lightning indices (LIs) based on updraft strength recorded in the Kanto region of Japan: (1) the relationship between CG lightning frequency and LIs based on updraft strength, and (2) the relationship between the occurrence of CG lightning and LIs based on updraft strength. Data from two X-band polarimetric radars recording at a high temporal resolution (every 1-2 min) were used to investigate updraft evolution associated with CG lightning activity. The LIs of updraft volumes were found to be well correlated with CG lightning frequency for threshold values of updraft speeds of > 5 and > 10 m s(-1) (correlation coefficient (r) > 0.7); this result supports the findings of a previous study in the North America. The LIs derived from updraft strength studied here, updraft volumes at vertical velocities of > 0, > 5, and > 10 m s(-1) and maximum updraft speed, were also well correlated with the occurrence of CG lightning (the highest hit rate (HR) was > 0.7 when probability of detection (POD) was > 0.9). The results demonstrate the potential for updraft parameters to be used as more accurate LIs than those based on reflectivity parameters.