Annual and Secular Changes of the Atmospheric Turidity in Japan

Abstract

It has been proved that the urban atmosphere affects solar radiation. The turbidity factor of Hausner-Dubor (τO) is obtained through reducing Linke's turbidity factor (τG) to mean sea level. τO is much exacter in comparing turbidities at many places. The aim of this study is to assess annual and secular changes in the atmospheric turbidity all over Japan by using the data of τO's monthly avarages, with the number of observations taken into account, made at 12 places in Japan (Fig. 1) from 1960 to 1982.Annual changes are mainly divided into two patterns. In the first, τO rises to the maximum in June or July, and declines symmetrically. In the second, it reaches the maximum at the same time, but drops suddenly in the autumn (Fig. 2).Atmospheric turbidity has a characteristic pattern of annual variation. It is low in the winter (Dec. -Feb.) and increases in the spring (Mar. -May). It is high in the summer (Jun. -Aug.) and decreases gradually or suddenly in the autumn (Sep. -Nov.).Normallly secular changes of τO are lager at 15:00 than those at 9:00. In the late 1960's, we find peaks occurring all over Japan, but in the late 1970's and 1980's, peaks or rising trends appear at different places (Figs. 3, 4).Since secular changes differ from one place to another, and the number of observation places is limited it is difficult to assess the τO secular trend for the whole of Japan.