On the Distribution of Relative Humidity in Tokyo and its Secular Change in the Heart of Tokyo

Abstract

In the author's work Local Climatology published in 1950, he gave some descriptions on the distribution of relative humidity by using the data observed at ten o'clock every day in 1935 at seven climatological stations in Tokyo, in which he emphasized that the relative humidity in the heart of Tokyo was less than that in the suburbs of this metropolis by about 5% (Fig. 1). It was reported that the relative humidity is higher in the suburbs than in the heart of Tokyo primarily due to lower temperature in the suburbs. As a result of this study, however, the aqueous vapour tension is also higher in the suburbs, causing higher relative humidity. Another result of this study is concerned with the secular change of relative humidity. By examining the data obtained every day continuously from 1876 to 1955 at the Central Meteorological Observatory situated in the heart of Tokyo, about 6% decrease in relative humidity was recognized for this 80-years period. However, the tension of aqueous vapour has been almost equal and the air temperature has in-creased by about 1.2°C for this period. Therefore, the decrease of relative humidity in the heart of Tokyo is mainly explained by the increase of air temperature. In Fig. 2, it is possible to see that the points representing relative humidity and air temperature in every five years for the period distribute symmetrically for the most part, in other words, a close negative correlation is recognized.