Water vapor budget in the lower stratosphere over Japan.

Abstract

The water vapor budget in the lower stratosphere over Japan was studied. At Kagoshima and Tateno the observed water vapor mass mixing ratio is explained by a modified Brewer circulation model adding the water vapor source of CH4 oxidation except in spring at Kagoshima. The vertical eddy diffusion coefficient at an altitude of 20.7 km was estimated to be 1.2-1.4×103cm2sec-1 from the vertical profiles of water vapor and the production rate of water vapor by the oxidation of CH4. Seasonal variation of the residence time of water vapor in the lower stratosphere was obtained; minimum in winter-spring (0.3 year) and maximum in fall (0.95 year). Mean vertical velocity of the return Hadley circulation (the descending branch of the Hadley circulation) was estimated to be 0.010-0.035cm sec-1. Water vapor in the lower stratosphere at Sapporo cannot be explained by the same model as Tateno and Kagoshima except in spring. A very low water vapor mixing ratio is observed in spring from Kagoshima through Sapporo and in winter at Sapporo, suggesting some water vapor removal processes. Aerosols in the lower stratosphere make negligible contribution to the water vapor budget except after an extensive volcanic eruption.