Diurnal variations of precipitation during the warm season over China

The spatial distribution and seasonal change of diurnal variations of precipitation during the warm season (May-September) over China were analysed using hourly data from 62 rain gauges during 1954-2001. Nocturnal precipitation predominates for the stations over the Tibetan Plateau as well as in south-west and north-west China. For stations to the east of about 110 degrees E, daytime precipitation predominates in the northern and southern parts, whereas nocturnal precipitation predominates in the middle and lower reaches of the Yangtze River and the North China Plain. Further, the magnitude of diurnal variations first decreases and then increases from the south towards the north. Two stations located close to the Bohai Bay manifest morning maxima. The significant diurnal variations in vertical circulation (stronger during the day and weaker at night), the meso-local-scale mountain-valley winds, and the nighttime cooling of cloud tops could be the processes behind the nocturnal rain in the western part of China (to the west of about 110 degrees E). Daytime precipitation in the eastern part of China (to the cast of about 110 degrees E)could be attributed to the moist convection connected with solar heating. The morning peaks for stations in the middle and lower reaches of the Yangtze River and the North China Plain and the magnitude changing pattern in the eastern part seem to be connected with the advance and retreat of the East Asian summer monsoon. The morning maxima at coastal stations may be mainly attributed to the local land-sea breeze. The seasonal changes of diurnal variations for the western part of China are relatively small, with nighttime precipitation maxima remaining fairly constant during the warm season. This part is not directly influenced by the monsoon. For most of the stations in the eastern part, morning peaks tend to be strengthened/weakened along with the East Asian monsoon's advancing/retreating. Copyright (c) 2008 Royal Meteorological Society