Diurnal variation of convective activity and precipitable water over the "semi-basin" - Preliminary study on the mechanism responsible for the evening convective activity maximum-

Abstract

The relationship between the diurnal variation of convective activity and precipitable water was examined in summer seasons using water vapor radiometer, C-band radar and radiosonde data. Convective activity over the "semi-basin" exhibited a diurnal variation with dual peaks at 15-17 JST and 19-20 JST, and the SSI (Showalter Stability Index) decreased from morning to evening due to the increase of water vapor in the lower layers associated with a thermally induced local circulation. When precipitable water exhibited a pronounced diurnal variation, the evening convective activity maximum (19-20 JST) was evident and cumulonimbus clouds had a tendency to develop over a limited region south and east of Mt. Haruna. On average the convective activity maximum occurred about an hour before the precipitable water maximum, and when precipitable water reached a maximum at an early (late) time, cumulonimbus clouds also formed at an early (late) time. Furthermore, the mechanism responsible for the evening convective maximum over the "semi-basin" is discussed, based on the results of the diurnal variation of convective activity and precipitable water.