宁夏春季首场透雨出现日期及环流背景分析

选用1961-2005年宁夏20个主要站降水量,分析春季首场透雨出现日期的气候特征,得出其年际、年代际变化特征不明显,在70年代以前、80年代中期到2000年这两个时间段里有4～5年周期变化,1970-1992年,首场透雨出现日期趋势在1982年前后发生了较大的转折,前期透雨出现偏晚,后期出现偏早.研究春季首场透雨出现日期典型偏早年与偏晚年环流背景,发现宁夏透雨出现早晚对海温有很好的响应,同时偏早年、偏晚年环流特征存在明显差异:偏早年前期海温以暖水位相为主,且3～4月宁夏处在500 hPa高度场正负距平交汇处,冷空气可以源源不断地进入,孟加拉湾洋面上水汽向北输送,给宁夏带来充足的水汽条件;偏晚年前期海温以冷水位相为主,受脊前西北气流控制,不利于宁夏冷空气出现,从贝加尔湖伴随冷空气带来的向南输送的水汽影响宁夏,由于量小,不能带来明显的降水.

Analysis on the Occurrence of First Soaking Rainfall and Its Circulation Background in the Typical Years in Ningxia

According to the precipitation data observed by the main stations in Ningxia Hui Autonomous Region during the period of 1961 -2005, in this paper the characteristics of first spring soaking rainfall are analyzed. It is found that the characteristics of first spring soaking rainfall in the study area are not so obvious. There were the 4-5-year cycles before the 1970s and during the period from the mid-1980s to 2000. During the period from 1970 to 1992, the occurrence of first spring soaking rainfall changed significantly around 1982, that is the first spring soaking rainfall occurred latter before 1982 but earlier after it. After researching the circulation background related to the first spring soaking rainfall, it is found that the response of the occurrence of first spring soaking rainfall to the sea temperature is sensitive, and the circulation flow in the years when the first spring soaking rainfall occurs earlier is significantly different from that in the years when the first spring soaking rainfall occurs latter. Sea temperature is increased in the years when the first spring soaking rainfall occurs earlier, the 500-hPa height field over Ningxia in March and April is located in the junction of the positive-negative anomaly, the cold airstream and the vapor flow from the Bay of Bengal come steadily to Ningxia. Contrarily, the sea temperature is decreased in the years when the first spring soaking rainfall occurs later, and such situation is disadvantageous for the occurrence of the cold airstream over Ningxia due to the effect of northwest air current in high front, so rainfall is less because of the limited vapor flow from the Lake Baikal.