On the Vertical Distributions of Condensation Nuclei

[摘要] Observations of Aitken nuclei were made at various heights of Mt. Fuji (3778m, 2800m, 1290m, 450m.) in Aug. 1947 and Jan. 1948. Th periods of observations in both cases were about ten days. Prevailing air masees on these days were mostly Tm (Ogasawara) in Aug. and Pc (Siberia) in Jan. The results obtained were as follows:(1) The diurnal variation showed one mountain-type curve at each height and seaon The maximum values occurred in the afternoon and the minimum occurred during midnight and early morning. The time of occurrence of maximum values were nearly the same each height and season, i.e., no systematic variationss were found.(2) The range of daily variation decreased with height.(3) The number of nuclei decreased exponentially with beight, and the lapse-rate was greater in winter than in summer.(4) The number of nuclei was greater in winter than in summer at the lower layer, but at the upper layer it was greater in summer than in winter. Thus, a layer having a constant number of nuclei seems to exist throughout a year.(5) Considerable discontinuities of lapse-rate were found at about the height of 1, 000m in summer and 1, 000 and 2, 000m in winter. These seemed to be brought by the effect of surface conditions of the earth to the original lapse-rate of each air mass.(6) On the nuclei spectrums it was found that (a) most of all Aitken nuclei became active at the ratio of expansion 1.05. (about 150% relative humidity) (b) there were many spontaneous condensation nuclei at each height in summer, but there were hardly any such nuclei existing in winter.(7) After some calculations it was known that the diurnal variation will likely occur mainly by transportations of nuclei due to the upward and downward air currents along the slope. Thus, it seemed to be concluded that the range of diurnal variation would be greater in mountainous regions than in free atmosphere.(8) The equilibrium of nuclei in the atmosphere seemed to be explained quantitatively by the upward transportation of nuclei due to eddy-diffusion and downward transportation due to rain drops which were formed from the coalescence of cloud particles built around nuclei.(9) The mean lapse-rate of nuclei was theoretically discussed on the ground of disappearence process of nuclei by rain drops stated above.(10) So to speak, the “non-meteorological nuclei”, which are Aitken nuclei but not able to grow into fog particles in free atmosphere because of their small activity, may be absorbed into the cloud particles already suspended in the air due to Brownian movement. On the other hand, the chance of such collisions may become negligibly small when the number of these nuclei becomes smaller than some definite number (less than 10 per c. c. of air). Thus it seems to be concluded that the non-meteorological nuclei will not decrease less than this definite number throunghout the whole column of the air. (Feb. 1948)

[学科分类] 大气科学