Abstract:

Based on precipitation data from 20 meteorological stations，atmospheric circulation characteristic quantity and NCEP reanalysis data in recent 50 years in Ningxia，the spatial － temporal distribution of the drought events and anomalous characteristics of general circulation in severe drought years as well as in cold and warm period were analyzed，and the relationship between drought events and sea surface temperature was also analyzed． The results indicated that in recent 50 years，the probability of drought occurrence was more in northern part than that in southern part of Ningxia，and drought events increased since 2000． In cold and dry years，while the dynamic conditions existed，but lack moisture and weak south branch stream resulted in less rainfall． In addition，powerful Qingzang high at the level of 200 hPa resulted in fine weather in Hetao area． In warm and dry years，the warm ridge existed over Mongolia and China at the level of 500 hPa height field，and anticyclonic circulation over northeastern part of Qinghai － Tibetan plateau and easterly and northerly winds over Hetao area at 200 hPa and 700 hPa led to the weak cold air and lack moisture over Ningxia． EL Nino events and warmer SST over Tropical Indian Ocean affected atmospheric circulation，which caused the moisture transportation path more southerly，and cold air was weaker and cold air path was more northerly． Under these conditions，the possibility of drought in Hetao area was larger．

Key words: Ningxia, severe drought, climatic characteristics, cause, atmospheric circulation, ocean background

摘要：

利用近50 a 宁夏20 个主要气象站降水序列、大气环流特征量、NCEP 再分析的高度场、风场、海温等资料，研究了宁夏7 月干旱事件的时空分布规律及相对冷、暖背景下严重干旱事件的大气环流异常的特点、干旱事件与海温异常的联系。结果表明: 近50 a 来，宁夏干旱事件发生的概率北部多于南部; 2000 年以来，发生干旱的几率增加。冷干年，虽具备降水的动力条件，但南支气流明显偏弱，水汽条件缺乏; 此外， 200 hPa 强盛的青藏高压，造成河套地区天气晴好; 暖干年， 500 hPa 高度场上蒙古国及我国河套一带暖性高压脊的存在，及700 hPa、200 hPa 风场上青藏高原东北侧的反气旋环流、河套地区偏东风和偏北风，造成宁夏冷空气活动偏弱，水汽条件缺乏。厄尔尼诺事件及热带印度洋海水的偏暖，影响大气环流异常，造成水汽输送偏南，冷空气强度偏弱，且位置偏北，进而造成河套一带形成干旱的可能性较大。
 

关键词: 宁夏地区, 严重干旱, 气候特征, 环流成因, 海洋背景