2011年春季中国北方沙尘天气过程及其成因

2011年春季,中国共出现了7次沙尘天气过程,其中沙尘暴4次,强沙尘暴2次,沙尘天气频次总体偏少、强沙尘暴偏多,影响范围较广.通过对2010-2011年冬季及2011年春季天气气候特征的分析表明:①2010/2011年冬季,冷空气偏强,气温偏低,有利于土壤冻结,同时新疆大部、内蒙古西部及东北部分地区降水偏少,使得前期地面植被状况偏差,进入2011年春季,中国北方大部地区降水仍偏少,地面植被状况虽未得到改善,但气温仍偏低,土壤解冻较晚,而2011年春季冷空气较常年偏弱,使得2011年沙尘暴发生时间较常年偏晚,且沙尘天气过程偏少；②中国北方沙尘天气常发区域土壤湿度较常年偏高,土壤状况良好,土质不够疏松,是2011年春季沙尘天气偏少的一个重要因素；③2011年春季蒙古国及内蒙古大部地区纬向风为偏西风的负距平区,不利于起沙及沙尘粒子向东输送.

The Frequencies,Severities,and Driving Factors of the Sand-dust Weather Processes Occurred in Northern China in the Spring of 2011

There occurred totally 7 sand-dust weather processes,  including 4 sandstorm processes and 2 severe sandstorm processes, in northern China in 2011. In comparison to the long-term means, the frequency of the sand-dust weathers was lower, the intensities of the sand-dust weathers were bigger, and the affected area was larger. The possible driving factors on the characteristics mentioned above were as follows: (1) The lower atmosphere temperature in the winter of 2010/2011 was beneficial to keep the soil frozen longer. Although the precipitation amount was less in the studied area in the winter of 2010 and spring of 2011, which led to a bad vegetation condition in the spring of 2011, the atmosphere temperature was still lower and the soil thawed out lately, which might restrain the occurrence of the sand-dust weathers in early spring, thus resulted in the fewer sand-dust weather processes in 2011. (2) The soil moisture content was higher in the studied area in the winter of 2010 and spring of 2011 than that in the other years, suggesting that the fine soil particles could not be blown up easily to form a sand-dust weather process; (3) In the spring of 2011, in most regions of Mongolia and Inner Mongolia, the zonal wind was the negative anomaly of westerly wind, which goes against the dust emission and conveying the dust particles to east.