Meteorological factors producing variation of tritium concentrations in Fukuoka, Japan

Abstract

Tritium concentrations of rain and river water in Fukuoka, Japan were determined by in combination of electrolytic enrichment of tritium and liquid scintillation counting. A cyclic seasonal variation is observed for tritium concentration in rain: high in winter/spring and low in summer/autumn. The detailed examination of the seasonal variation using the back trajectory analysis suggests that rain clouds arrived at Fukuoka from the Eurasia continent have higher tritium concentration than those from the Pacific Ocean. The seasonal change is concluded to be determined by migration pathway which is strongly dependent upon meteorological factors in Fukuoka. The river water of Tatara River has lower tritium concentration than rain and does not show a cyclic variation observed on rain, showing smoother change than rain, which indicates continuous supply of groundwater contained old rain to the river water. The difference of tritium concentrations between river water and rain suggest that the residence time of the groundwater should be longer than 6.8 years.