Diurnal cycle of precipitation and its possible causes: A case study in Shandong Province, China

Accurate information on diurnal precipitation variations is essential for understanding the mechanism of precipitation formation, assessing the regional climate characteristics, and improving the simulation performance of climate models. Taking Shandong Province, East China, as a case study, 123 stations with hourly observational precipitation data were divided into three categories by the harmonic analysis on diurnal variation of precipitation, and the diurnal variations in precipitation amount, frequency and intensity were further analysed to derive the precipitation partition. The results showed that: (1) the peak precipitation frequency at different types of stations occurred steadily around 0400-0600 LST, whereas the peak precipitation intensity existed at different moments such as 0200 and 1700, and precipitation amount mostly showed a double-peak pattern in the early morning (0400-0600 LST) and late afternoon (1600-1800 LST); (2) early morning precipitation was mainly driven by persistent precipitation, which contributed between 65.2% and 84.3%, while precipitation peaks in the late afternoon with a significant increase in the contribution of short duration precipitation; and (3) the influence of mountain-plain circulation and the increasing effect of topographic uplift on precipitation may be the main reasons for the formation of early morning precipitation peaks. The strength of sea-land winds and local convection was also key factors affecting the diurnal variation of precipitation.