黄河中上游季节内强降水的时间非均匀性特征及其对大气环流的响应

应用1960-2008年5-10月黄河中上游流域66个气象台站降水资料和美国环境预测中心及大气研究中心(NCEP/NCAR)再分析资料,综合气候分区及地表水系分布情况,将黄河中上游流域分为高原区、干旱区、季风影响区,以强降水集中度(SCD)和强降水集中期(SCP)来表征强降水的非均匀性特征,并对SCP异常年份的强降水的变化特征及环流形式进行分析.结果表明:①黄河中上游流域大部分地区强降水依赖化的特征显著,强降水分布最为均匀的地区为秦岭北麓及山西南部,降水最为集中的地区为河套地区及陕北等地.②在黄河中上游流域,3个区强降水平均发生的时间先后顺序为季风影响区最晚、干旱区次之、高原区最早,且均相差一候；黄河流域季风影响区的南部渭河、泾河、洛河等处及青藏高原东部的兰州附近为大的SCP变率区,强降水发生的时间变动较大,鄂尔多斯高原东北部为小的SCP变率区,强降水发生时间稳定；干旱区与季风影响区汛期SCP于20世纪90年代初期发生由大变小的显著性突变,且干旱区突变提前于季风影响区.③干旱区汛期SCP异常年份的高空环流显示,当西太平洋副高北抬至30°N以北120°E左右、南亚高压维持在30°N左右120°E以东时,若两高压“同进同退”(“同向而进、背向而退”),则强降水发生在汛期(7月中旬8月下旬)后(前)期.黄河流域季风影响区强降水异常年份的高空环流显示,当西太平洋副热带高压维持在26°-30°N、120°E左右,南亚高压维持在30°N左右、120°E以西时,若两高压“同进同退”(“同向而进、背向而退”),则强降水发生在汛期后(前)期.

The Intra-Seasonal Heterogeneity of the Strong Precipitation Events and the Corresponding Atmosphere Circulation Characteristics in the Middle and Upper Yellow River Basin in Flood Season

Based on the daily precipitation data collected in May through October during 1960-2008 and the NCAR/NCEP reanalysis data, we analyzed the characteristics of the rainfalls in the middle and upper Yellow River basin in flood season and the corresponding atmosphere circulation pattern. The studied area could be divided into plateau area, arid area and monsoon area if the climate zone and the local river system were concerned. The heterogeneity of the three areas was evaluated with the strong precipitation concentration period (SCP) and the strong precipitation concentration degree (SCD). The results were summarized as follows: (1) The dependence of the precipitation on the strong rainfall was obvious in most area of the middle and upper Yellow River basin. The middle Shannxi Province and southern Shanxi province had fare intra-seasonal even distributed rainfalls, while Hetao area and northern Shaanxi province had some strong ones. (2) The average occurrence dates of the strong rainfall in flood season in plateau area was the earliest, followed by that in arid area, and then in monsoon area with a five-day delay. In south of the monsoon area, just Weihe, Jinghe and Luohe Basin and in east of the plateau area, the SCP changed greatly. In the 1990s, there took place significant decrease mutations of the SCP both in arid area and monsoon area, and that in arid area was earlier than that in monsoon area. (3) In the arid area, the high circulation situation in the SCP anomalous years showed that there would be strong rainfall in front of or behind of the flood season when the Western Pacific Subtropic High (WPSH) at 500 hPa on the northern side of 30°N, around 120°E, and the Southern Asia High (SAH) at 200 hPa on the eastern side of 120°E, around 30°N, moved towards each other or backwards each other. In the monsoon area, there was the same phenomenon as in the arid area when the WPSH located in 26°-30°N, around 120°E, meanwhile the SAH on the western side of 120°E, around 30°N.