Diurnal variation of summer precipitation across the central Tianshan Mountain

Abstract

he climatic features of the diurnally varying summer precipitation over and around the central Tianshan Mountain are investigated. Both the hourly rainfall data observed at eight stations along a transect across the mountain and the convective index derived from the satellite data show that there are three distinct regimes: the early morning peak at stations to the south of the mountain, the late afternoon peak at stations on the mountain, and the night peak at stations to the north of the mountain. The relation between regimes of diurnal variation is analyzed. Through defining the regional rainfall event (RRE), the initial stations of each RRE are recorded. The early morning rainfall in the southern periphery of the mountain is triggered locally in the southern basin. Both the late afternoon peak over the mountain and the night peak in the northern periphery are contributed by mountain originated rainfall events. These rainfall events appear over the mountain in the afternoon and some of them move northward and lead to the nocturnal rainfall in the northern basin. The triggering of convection in the afternoon over the mountain and that in the early morning in the southern basin are related to the diurnally varying wind and thermodynamic conditions over and around the mountain. Low-level convergence with thermodynamic instability appears at noon (night) over the mountain (in the southern basin) just before the start of the convection.