DEW POINT ELEVATION AND OXYGEN AND HYDROGEN ISOTOPIC RATIOS FOR PRECIPITATION SAMPLED AT OSAKA AND MATSUE, JAPAN

Abstract

Dew point elevation was clarified to be an important factor determining stable isotope values of precipitation. When dew point elevation is high, stable isotope values for precipitation were clarified to increase due to the evaporation process which occurred during dropping from dew point elevation to the ground. In winter wet air from the Japan Sea passes over mountains in the center of Japan and dry air after precipitated at the mountains reaches at the Inland Sea. Subsequently, it is thought that when dew point elevation increases, stable isotope values for precipitation increase with the distance from dew point elevation to the ground then high dew point elevation raises the average isotope value of precipitation. Therefore, the elevation of the precipitation point decreases with an increase of the isotope value. Consequently, altitude effect is thought to be caused by precipitation with high dew point elevation. High dew point elevation and high stable isotope values for precipitation in winter were observed at Osaka in the Inland Sea. On the other hand, these high values at Matsue on the Japan Sea side in winter were rarely observed because of low dew point elevation with wet air.