On Vortical Mesoscale Disturbances Observed During the Period of Heavy Snow or Rain in the Hokuriku District

摘要

During the period of heavy and concentrated snow-or rainfall in the Hokuriku District, vortical mesoscale disturbances have often been observed by radar. These vortical disturbances are characterized by a diameter of about 50 to 80km, which is 100 times as large as that of tornado, and one order of magnitude smaller than that of typhoon, and may be classified as mesocyclone. Radar observations show the remarkable spiral or ring-shaped radar echoes corresponding to vortical disturbances. They usually develop off the coast. move across the plain and disappear in the mountain area of the Hokuriku District, having the lifetime of several hours. Further, it was found that the heavy and concentrated snow-or rainfalls sometimes took place along the track of these vortical disturbances, and that the intensity of precipitation may be estimated by means of wind divergence and the concept of vortical rain like the rain due to typhoon.