西北地区东部干旱化与天气体系演变的关系

用EOF、PDF和场相似理论相结合的方法，分析了近20a来西北地区东部夏季代表月份干旱化与天气体系演变的关系。指出夏季代表月份东亚大气环流存在两类天气体系(Weather Regimes)，即A类和B类。A类与西北地区东部干旱环流型相对应；B类与西北地区东部偏涝环流型相联系。研究结果表明：近20a来，西北地区东部夏季代表月份与天气体系A型(干旱型)正相似日数有逐渐增多的趋势，与天气体系B型（偏涝型）正相似日数趋于减少。

Aridification of Summer in the East of Northwest China and Weather Regimes

The possible reason for the aridification of the representative summer month (July) in the east of NW China in the last twenty years is investigated by a method combined with the EOF,probability density function and the similarity of two fields.It is for the first time pointed out that there exists two weather regimes in July East Asian atmospheric general circulation,namely the A regime and B regime.The A regime is associated with the drought circulation pattern for the east of northwest China,and the B regime with the comparatively wet pattern.The possible reason for the aridification of summer in the east region of NW China in recent 20 years is that the frequency of positive similarity with the A regime (drought pattern) persistently increases and the frequency of positive similarity with the B regime (comparatively wet pattern) persistently decreases.