〈Original Papers〉Modulation of diurnal precipitation occurrences observed in the Tibetan Plateau during monsoon season of 1998

Abstract

Relations between the diurnal change of the radar echo areas and surface condition were examined at the central Tibetan Plateau during the monsoon season in 1998. During the late June, under the synoptic conditions of prevailing surface heat low with Tibetan anticyclone, a weekly time scale modulation was clearly observed in the diurnal changes of the convective activity, such as the delay of the daytime precipitation clouds toward evening, especially over the southern mountainous areas. The feature was confirmed by the diurnal weather changes indicated by multiple surface meteorological elements. Surface energy flux and hydro-meteorological measurements showed that the modulation was associated with weekly scale reducing of morning sensible heating and suppression of the planetary boundary layer development during midday. The increase of soil-surface moisture in the morning was also confirmed by the surface albedo measurements. Therefore, we hypothesize the cause of the delay of daytime precipitation by land-surface moistening due to precipitation in the previous days