Three-Dimensional Radio Images Of Winter Lightning In Japan And Characteristics Of Associated Charge Structure

We conducted lightning observational campaigns using a three-dimensional (3D) lightning mapper called the Broadband Observation network for Lightning and Thunderstorms (BOLT) and C-band radar to further understand the distinct characteristics of winter lightning in the coastal area of the Sea of Japan. We succeeded in locating 3D intracloud (IC) flashes, cloud-to-ground (CG) flashes, and upward lightning during winter. The basic characteristics of winter lightning, such as leader speeds and charge structure associated with an IC discharge, are similar to summer lightning. A noticeable difference between the winter lightning and the summer lightning is that the altitudes of the source locations associated with winter lightning are substantially lower than those associated with summer lightning. We performed a statistical comparison of winter and summer lightning. This comparison shows that the BOLT source altitude distributions during winter and summer peak at 2.1 and 7.5 km, respectively. Conversely, the distributions of the BOLT temperatures, which are the temperatures corresponding to the BOLT source altitudes, during both winter and summer show similar trends and have large values near -10 degrees C. These results indicate that a similar charge separation process, likely a noninductive charging mechanism, primarily contributes to thunderstorm electrification during both winter and summer. We show that the horizontal extent of the winter flashes is substantially larger than that of the summer flashes. This result implies that the charge regions in winter thunderstorms cover a wide area and, therefore, produce CG flashes with large charge transfers. (c) 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.