On the occurrence of Waterspout in the Neighbourhood of Japan

Abstract

By the investigation of 89 waterspouts which occurred during the 23 years, from 1926 to 1947, we obtained the statistical results as follows:
(1) The cause of occurrence were classified into types of cold front, warm front, high pressure area, frontal zone, convergent line, Taiwan depression and head thunderstorm.
(2) The number of occurrence is maximum in September and minimum in April.
(3) Waterspouts which were caused by cold fronts amount to 57% of all, and they mostly occur in the Japan Sea side and they were maximum in number in September.
A typical pressure pattern of occurrence is that of cold front accompanying cyclones and others are those accompanying Siberian high pressures, as well as Manchurian, North or Middle China and Japan Sea high pressures, and local cold fronts of Boso peninsula. The number of occurrence shows a maximum in the afternoon. The number is small in the morning and in the evening.
(4) Waterspouts caused by warm fronts are 17% of the whole number, and they occur only in the Pacific Ocean in the monthes of June to September. There are two types of pressure patterns of this case, the one accompanying typhoone and the otter accompanying typical fronts. The former occurs in any plac_??_ from Loochoo Islands to Kanto district, but the latter is limited only to areas west of Kii peninsula. (5) Waterspouts which occurred in the high pressure area were limited to the area to the south of Loochoo Islands and to Hokkaido. The former cases mostly occurred in the summer seasons and the latter cases in autumn. Time of occurrence is limited to the houre of afternoon excluding night time.
Collecting the Data (surface observation, Pilot, Radiosonde) the author found, some interesting and remarkable facts as follows.
(1) For the occurrence of waterspouts, it is necessary that sufficient energy of unconditional instability or discontinuity of wind in the where between 1, 000m to 2, 000m should exist in the atmosphere, but, it is not necessary that both of thse exist together.
(2) Layer in which the waterspouts occur is very unstable and it disappears very easily.
(3) Seasonal difference in strength of waterspouts is not recognized but the waterspouts which occur in high pressure area arc weaker than those that occur at the fronts. More detailed investigation about these remarks will be reported by the author in the near future.