利用2010—2016年5—6月ERA5逐小时再分析数据集和国家气象信息中心逐小时降水量融合产品，对影响华南地区的低空急流事件进行筛选和分类，并分析天气系统相关的低空急流（Synoptic-system-related low-level jet，SLLJ）和边界层急流（Boundary layer jet，BLJ）的日变化及其影响下的华南降水日变化的时空分布特征。结果表明，BLJ和SLLJ在白天减弱、夜间增强，并在凌晨达到峰值，其日变化主要与边界层惯性振荡引起的非地转风的顺时针旋转有关。双急流日华南地区降水量显著增加，且降水日变化有明显的区域差异，与双急流的演变和配置密切相关。广西中北部主要为SLLJ左前方发生的夜间山区降水，且降水量仅有凌晨的单峰。广西沿海和广东地区存在早晨和午后两个峰值，BLJ出口区辐合和SLLJ入口区辐散的维持有利于降水频率的增大，从而导致午后峰值的出现，而早晨的峰值除了受双急流有利配置的影响外，主要归因于急流夜间增强的日变化过程所致的早晨降水强度的增加。
Based on the ERA5 hourly reanalysis data and the merged hourly precipitation products from National Meteorological Centre from May to June of 2010-2016, low-level jet events over South China are selected and classified using an objective method. The diurnal cycles of boundary layer jet (BLJ) and synoptic-system-related low-level jet (SLLJ) are also investigated during early-summer, as well as their influence on the temporal and spatial distributions of the diurnal cycle of precipitation over South China. The results show that BLJ and SLLJ weaken during daytime while intensify during nighttime, reaching their peaks in the early morning. The diurnal cycles are found to be associated with the clockwise rotation of ageostrophic winds caused by boundary layer inertial oscillations. The precipitation over South China affected by the double low-level jets increases significantly, which shows obvious spatial differences with respect to the diurnal cycle due to the evolution and configuration of double low-level jets. The precipitation in central and northern Guangxi is mainly concentrated over the mountainous area at the left anterior to the SLLJ at nighttime and is characterized by only one single peak in the early morning, whereas in Guangdong and the coastal areas of Guangxi, there are two peaks in the morning and afternoon, respectively. The maintenance of convergence at the BLJ’ exit and mid-level divergence near the SLLJ’s entrance are conducive to the increasing frequency of precipitation and hence emerge the peak in the afternoon. In addition to the favorable configuration of the double low-level jets, the morning peak of precipitation is also attributed to the peak of precipitation intensity caused by the enhanced double low-level jets at nighttime in the diurnal cycle process.
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