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A Study of Radar Echoes and their Relation to Lightning Discharges of Thunderclouds in the Hokuriku District

1993; The Meteorological Society of Japan; Volume: 71; Issue: 2 Linguagem: Inglês

10.2151/jmsj1965.71.2_195

2186-9057

Koichiro Michimoto,

Meteorological Phenomena and Simulations

In the present work, winter thunderclouds and active convective clouds were observed by means of radar with CAPPI (Constant Altitude Plan Position Indicator). The lightning activity is monitored by a local network of sferics direction finders around Komatsu Airport.In midwinter, from January to early March, active convective clouds, 30 dBZ echo tops of which develop up to the -20°C temperature level, exhibit very weak lightning activity called "Single-Flash Storm", or sometimes fail to generate even a single lightning discharge. The altitude of the -10°C temperature level is between 1.8 to 1.4km in the former case. On the other hand, it is lower than 1.4km in the latter case. These significantly low altitudes of the -10°C temperature level are the main reason for keeping such clouds in a weak or non-lightning situation.Concerning the classification of the lightning activity, the author has proposed the following criteria:(a) When the altitude of the -10°C temperature level is higher than 1.8km, clouds exhibit strong lightning activity.(b) When the altitude of the -10°C temperature level is between 1.8 to 1.4km, clouds exhibit very weak or no lightning activity.(c) When the altitude of the -10°C temperature level is lower than 1.4km, clouds never generate a lightning discharge.Along with the results of thundercloud investigation stated in Part I of the present article (Michimoto, 1991), it is concluded that the necessary conditions for convective clouds to generate lightning discharge are as follows:(1) The 30 dBZ echo of the clouds has to develop at a level higher than the -20°C temperature level.(2) The altitude of the -10°C temperature level has to be higher than 1.4km.(3) The clouds have to involve rapid development of graupel particle precipitation; specifically, they have to involve formation and rapidly vertical movement of 40-to-50 dBZ echo cells.