Abstract:

 Based on the daily temperature of 20 weather stations in winter from 1961 to 2013 in Ningxia，NCEP reanalysis data and the 500 hPa circulation field，the characteristics of temperature anomaly in winter since 2000 and the variation of the 500 hPa circulation were analyzed emphatically． The results showed that the average temperature and extreme minimum temperature had an obvious rising trend． The days of anomalous low temperature at night decreased significantly，while that of anomalous high temperature increased remarkably，and the decreasing trend was higher than increasing trend in most areas of Ningxia． The cold and warm extreme events occurred frequently since 2000，and the years of anomalous high temperature were more than that of anomalous low temperature． The frequency of lower winter mean temperature was the highest since the winter of 2007 /2008． There were four anomalous characteristics of the average temperature in phase during winter: (1) the temperature anomaly appeared primarily in January and February．(2) the amplitude of anomalous low temperature was greater than that of the anomalous high．(3) the difference of temperature between the two ten－days increased．(4) the coldest period had changed． From the decadal change of the average temperature，extreme minimum temperature and days of anomalous highness in the daytime in winter was the highest or next to the highest one，the days of anomalous low temperature at night was the lowest or next to the lowest one．The 500 hPa height fields over Ningxia had critical impact on winter temperature in Ningxia，and the variation of its intensity in decade and the colder or warmer year influenced directly the winter temperature anomaly． The abnormal low temperature in winter was more sensitive to the western Pacific subtropical high intensity index and westerly circulation index in Asia．

Key words: winter temperature, anomaly characteristics, 500 hPa circulation, Ningxia

摘要：

利用1961年以来宁夏冬季逐日气温资料及NCEP再分析资料和环流特征量资料，重点分析了21世纪以来宁夏冬季气温异常特征及同期500 hPa环流变化特征。结果表明:冬季平均气温和最低气温极小值明显上升，夜间气温异常偏低日数显著减少，白天气温异常偏高日数显著增加，大部分地区夜间气温异常偏低日数减少趋势大于白天气温异常偏高日数的增加趋势。21世纪以来，易发生极端冷暖事件，异常偏高年份多于异常偏低年份2007/2008冬季以后为1997年以来冬季平均气温偏低频率最高时段;冬季阶段性平均气温异常有4个特征:(1)气温异常主要出现在1月和2月;(2)异常偏低的幅度明显大于异常偏高的幅度;(3)相邻2旬间气温变化幅度增大;(4)最冷时段发生变化从年代际变化看，冬季平均气温最低气温极小值白天气温异常偏高日数为最高或次高值，夜间异常偏低日数多为最低或次低值500 hPa高度上宁夏上空是影响冬季气温异常的关键区，其年代际及冷暖年强度变化是造成气温异常的最直接原因。宁夏冬季气温对亚洲西风环流指数和西太平洋副热带高压强度指数的响应更加敏感。

关键词: 冬季气温, 异常特征, 500hPa环流, 宁夏