广西暴雨非均匀性分布特征研究

利用广西1979—2008 年83 个气象观测站的逐日降水和NCEP/NCAR 再分析资料,采用蒙特卡罗检验等方法,计算和分析广西暴雨非均匀性分布及其变化特征。结果表明,广西暴雨主要发生在汛期(4—9 月),暴雨总站次约占全年总数的9 成;年暴雨量占全年总降水量的比例随年际变化有增加的趋势,即以后发生极端强降水的可能性增大。广西暴雨集中度分布为桂东大于桂西,桂西北和沿海地区的暴雨集中度变化趋势大部分为正趋势,桂东南大部分为负趋势。桂东北和西南地区暴雨集中期最晚,百色北部山区和桂东南地区最早,暴雨集中期气候趋势是桂东大部分地区和沿海地区有偏晚趋势,桂中和桂西大部分地区有偏早趋势。冬春季青藏高原南部和西太平洋高度场负距平,夏秋季副热带高压偏强、面积偏大、脊线偏西,这种稳定的东高西低形势有利于广西暴雨集中度偏大。冬季青藏高原南部和西太平洋地区的高度场均为正距平,春夏秋季青藏高原南部及西太平洋高度场的周期性变化特征使广西暴雨集中度偏小。夏季风强(弱)的年份孟加拉湾向广西输送的水汽通量少(大),低空风速小(大),造成广西除了北部山区和北海以外大部分地区暴雨集中度偏小(大)。 

ANALYSIS ON INNER-ANNUAL INHOMOGENEITY OF RAINSTORM EVENTS IN GUANGXI

Based on the daily precipitation data of 83 stations in Guangxi and the NCEP/NCAR monthly reanalysis data from 1979 through 2008, the characteristics of spatial and temporal distribution and variation of the rainstorm-concentration degree (RCD) and the rainstorm-concentration period (RCP) are analyzed by using the methods of Monte Carlo test etc. The results are shown as follows. The rainstorm events are concentrated in April-September, taking up about 90% of the yearly total rainfall, and the percentages of rainstorms accounting for the annual total precipitation have an increasing tendency. RCD in the east of Guangxi is larger than that in the west. The RCP in the northeast and southwest of Guangxi is later than that in the other regions, and that in the northern mountainous regions of Baise and southeast Guangxi is the earliest. The RCD exhibits an increasing tendency in the northwest and the coastal region while showing a decreasing tendency in the other regions. On a long-term basis, the RCP in the east and coastal region has a postponing trend and that in the other regions tends to be earlier. The proposed mechanism is as follows: If the geopotential height in the south of Qinghai-Tibet Plateau and the West Pacific has a highly negative anomaly in winter, the western Pacific subtropical high is strong in summer, which will increase RCD in Guangxi; If the geopotential height has a highly positive anomaly in winter, the subtropical high has a significant periodic oscillation in summer, which will increase RCD in Guangxi. The value of RCD is high (low) in the area of northern mountainous regions of Guangxi and Beihai in strong (weak) South China Sea summer monsoon years, while in the other areas, the value of RCD is low (high).