资源环境科技发展态势分析平台

Heavy precipitation in Beijing is modulated by both synoptic forcings and local thermodynamic characteristics of troposphere, which has yet to be well known. This study investigated the large-scale synoptic patterns and local sounding features associated with the summertime heavy precipitation in Beijing, based on long-term surface meteorological observations, radiosonde measurements, in combination of reanalysis data from 2008 to 2017. The results show that the heavy rainfall occurs more frequently in late July, which is associated with the movement of subtropical anticyclone. The sounding parameters during the heavy rainfall days are examined as well. It is found that the heavy rainfall is often related to favourable convective conditions characterized by abundant water vapour and high unstable energy. The soundings for around 45% of heavy rainfall days in Beijing exhibit the pattern of thin tube (TT), and those for 25 and 20% of heavy rainfall days show the patterns of loaded gun (LG) and inverted V (IV), respectively. On average, the rainfall amount of TT is 55.8 mm/day, which is 3 mm/day (15 mm/day) higher than that of LG (IV). The more frequent and heavier rainfall observed for TT pattern is due to the high values of precipitable water and wind shear. On the large scale, three dominant synoptic patterns associated with heavy rainfall in Beijing have been identified using the T-mode principle component analysis. These synoptic patterns are all characterized by prevailing southerly winds within the lower troposphere, resulting in water vapours being easily transported from southern regions to Beijing, which in turn favours the occurrence of heavy precipitation. These dominant synoptic patterns and thermodynamic characteristics associated with the heavy rainfall in Beijing revealed in this study have important implications for better understanding of heavy rainfall in the North China Plain.