Long-Term Observations of Ice Nucleus Concentration in Tokyo

Abstract

The observations of ice nucleus concentration with the mixing type cold chamber have been continuously carried out at the Meteorological Research Institute for a long time. In an attempt to compare the data of ice nucleus concentration obtained from the present observation with those of the past, a study was made on the variations over a two-year period between April, 1968 and March, 1970. This period was selected in view of the continuity of observations during that time. The seasonal variation of the mean value of —20°C nuclei measured at 10 minute intervals reached a high of 66.2 nuclei per liter in winter, and a low of 7.6 nuclei per liter in summer. Measurements both in spring and autumn showed a value of a little over 20 nuclei per liter. Monthly speaking, January, February and December marked high values, whereas those of June, July and August were low. Especially, the lowest of the year appeared in August with 3.8 nuclei per liter. Thus, considerable monthly variation was recognized. As for the diurnal variation of ice nucleus concentration for each season, it was clearly observed that its curve tended to have more fluctuations in winter than in summer, and that in winter, the concentration was distinctly low at night and high in the daytime. The examination of the dispersion of the distribution of ice nucleus concentration indicated that, despite fewer fluctuations in the diurnal variation curve for summer and more fluctuations for winter, the value of standard deviations of ice nucleus concentration was smallest for winter and largest for summer. © 1979, Japan Meteorological Agency. All rights reserved.