【摘要】 从2010年秋天到2011年的春天,我国北方的冬麦区遭遇到了历史罕见的干旱灾害,大部分地区连续100天以上没有有效降水,直到2011年的2月25-27日出现了一次大范围的小到中雨天气过程,大大缓解了干旱。文中利用NOAA的北极涛动(AO)数据、NCEP/NCAR再分析数据和国家气候中心的高空格点数据等资料对这次降雨过程进行客观分析。结果表明:AO指数变化引起北半球的环流调整是可能出现大范围有效降雨的前期信号;中低空切变的出现为降雨提供了水汽辐合和上升动力条件,切变线的位置决定降雨的落区;中低空急流的出现和维持为降雨提供水汽条件,急流的强度和维持时间决定降雨量的大小。对久旱转雨的转折性天气过程应首先关注AO指数的变化和环流的调整,预报分析中应重点考虑切变线和中低空急流这两个指标。更多还原

【Abstract】 From the autumn of 2010 to the spring of 2011,the winter wheat regions were suffered an infrequent severe drought in North China,there were not valid rain for 100 or more days in most of the regions,until at 25 to 27 February 2011,a light to moderate rain weather process came to the regions,so the drought was relieved greatly.In this paper,based on the Arctic Oscillation(AO) data of NOAA,NCEP/NCAR reanalysis data,the high space-point data of National Climate Center,etc.,the rainfall process was analyzed objectively.The results showed that the change of AO indices could lead to the adjustment of atmospheric circulation in the Northern Hemisphere,it may be the early signal of a wide range effective rainfall.The emergence of the low-altitude shear could provide the convergence of moisture and upward dynamic conditions for the rainfall,the zone of rain falling could be determined according to the positions of the shear line.The emergence and maintainance of low-level jet could transport the moisture,the rainfall intensity could be determined by the intensity and duration of the jet.It was concluded that the AO changes and circulation adjustment should be primarily paid attention after a prolonged severe drought,if try to predict the turning-point rain process,the indicators such as shear line and low-level jet should be focused on.更多还原