知识与财富的链接
利用1961-2008年NCEP/NCAR(2．5°×2．5°)再分析逐月500 hPa高度场资料和1961-2008年西北地区东部陕、甘、宁、青4省170个气象观测站的月降水量资料,计算春季东亚北风指数,分析研究区春季降水的历史演变规律、东亚北风指数的年代际变化及其与西北春季降水的关联。结果表明:50 a来降水演变特点是以黄河为界,黄河以西降水呈增多趋势,黄河以东降水呈减少趋势,降水减少的幅度明显大于增加的幅度;特别是近20 a,黄河以东广大区域降水减少的幅度越来越大,干旱化趋势明显,而青海南部、河西走廊则降水呈增加趋势。在此期间,春季东亚北风逐渐增强,特别是20世纪90年代中期以后明显增强。进一步分析表明,当春季东亚北风偏强（弱）时,除青海南部外,西北地区东部大部分地方降水偏少（多）,即春季东亚北风异常增强,可引起西北地区东部黄河以东干旱少雨,导致干旱化加剧。
The values of spring East Asia north wind index were calculated based on the data of NCEP/NCAR reanalyzed monthly 500-hPa height field during the period from 1961 to 2010 and of monthly precipitation at 170 meteorological stations in Qinghai, Gansu and Shaanxi provinces and NingxiaHui Autonomous Region in the eastern region of northwest China. The history change of spring precipitation and the relationship between the decadal variation of East Asia north wind index and the spring precipitation in northwest China were analyzed. The results showed that, bordered by the Yellow River, precipitation was in an increase trend in the regions west from the Yellow River but a decrease trend in the regions east from the river. The precipitation decrease amplitude was significantly higher than the increase amplitude. Especially in recent 20 years, the precipitation decrease was more and more significant in the vast region east from the Yellow River, and the drought trend was obvious. Precipitation, however, was in an increased trend in south Qinghai Province and the Hexi Corridor in Gansu Province. The spring East Asia north wind increased gradually during this period, especially after the mid 1990s. Further analysis showed that, when the spring East Asia north wind was strong, precipitation was decreased in most areas of the eastern region of northwest China except in south Qinghai Province. So it could be concluded that the abnormal strong spring East Asia north wind could cause a decrease of precipitation and an aggravation of drought in the regions east from the Yellow River.
