河西走廊东部中雨及以上降水的气候特征及预报

Climatic Characteristic and Forecast of Precipitation over 10 mm in Eastern Hexi Corridor of Gansu

利用河西走廊东部武威市5个气象站1960～2009年降水资料,分析了该区域中雨及以上降水(日降水量≥10 mm)的时空分布特征。结果表明:河西走廊东部中雨及以上降水南部明显多于北部;各地中雨及以上降水日数的年变化不太一致,天祝、永昌、民勤呈增加趋势,凉州、古浪呈减少趋势。中雨及以上降水天气主要出现在4～10月,以7月、8月最多;强降水仅出现在5～9月,年降水量的多少与发生强降水场次关系很大。造成河西走廊东部中雨及以上降水环流形势主要有新疆冷槽东移南压型和西南气流型,充足的水汽条件、强烈的上升运动和不稳定能量是中雨及以上降水的必需条件。运用ECMWF数值预报格点场资料,采用Press准则进行因子初选,用逐步回归预报方法进行因子精选,使用最优子集回归建立中雨及以上降水预报方程,采用CSC双评分准则确定了各地中雨及以上降水预报的全局最优的显著性方程,采用拟合率和概括率同时最大的原则确定中雨及以上降水预报临界值和中雨及以上降水的定性预报。该模式具有较高的拟合精度和预报准确率,为中雨及以上降水的业务预报提供了客观有效的指导。

Based on daily precipitation data from five stations in Wuwei（located in east of Hexi Corridor） from 1960 to 2009,the spatial and temporal distribution of precipitation over 10 mm（daily precipitation ≥ 10 mm） was analyzed systematically in this paper.The results show that precipitation over 10 mm was more obviously in south part than that in north of east Hexi Corridor.Annual variation of precipitation days over 10 mm was not consistent in each region,and it presented increasing trend in Tianzhu,Yongchang and Minqin,but decreasing trend in Liangzhou and Gulang.The rainfall（precipitation over 10 mm） weather occurred maily in April to October,especially in July and August.Precipitation over 25 mm only occurred in May to September,and the annual precipitation correlated with occurrence times of precipitation over 25 mm.The circulation situations which resulted in precipitation over 10 mm in east Hexi Corridor were Xinjiang cold trough moving to east and south,and southwest air current,and the abundant water vapor condition,the intense lifting movement and the unstable energy were essential conditions.Based on data of ECMWF numerical forecast grid field,the factors were initially selected with Press criterion and selected accurately with stepwise regression forecast method,the forecast equations for precipitation over 10 mm were established with optimal subset regression.The most superior significance forecast equations of precipitation over 10 mm in each region were determined finally with the CSC double grading criterion.Forecast marginal value and qualitative forecast of precipitation over 10 mm were determined using principle that the fitting and the summary rate were the biggest simultaneously.