宁夏近60 a寒潮变化特征及其环流异常

Change characteristics and circulation anomaly analysis of cold wave in Ningxia over the past 60 years

利用1961—2020年宁夏逐日最低气温观测资料及同期位势高度、海平面气压场和风场逐月再分析资料,分析近60 a宁夏24 h、48 h、72 h不同历时寒潮、强寒潮、超强寒潮的时空演变特征,并进一步揭示寒潮变化的大气环流异常特征。结果表明:(1)宁夏近60 a不同强度、不同历时寒潮一致表现为“东多西少、北多南少”的分布特征,这与冷空气路径及宁夏地形有关。(2)全区寒潮、强寒潮、超强寒潮频次分别占全年总寒潮频次的71.7%、22.6%和5.7%,寒潮以24 h和48 h为主,而强寒潮及超强寒潮不同历时的频次比例相当;各类寒潮存在1—4月递减、10—12月递增的逐月变化特征。(3)宁夏近60 a寒潮、强寒潮、超强寒潮分别以4.5站次·(10a)^(-1)、2.8站次·(10a)^(-1)及0.18站次·(10a)^(-1)的速率减少,其中24 h及48 h短历时频次减少,但72 h长历时增多;且1960s最多,之后波动减少,1990s达到最少,2000s以来波动增多,20世纪80年代后期寒潮及强寒潮发生突变。(4)宁夏寒潮突变前后的大气环流呈现出完全相反的分布特征,之前环流形势利于极地冷空气活跃南下,之后则相反;但1961—2020年及突变前后宁夏寒潮的关键影响系统较为一致,当乌山阻高异常偏强、东亚大槽偏强、欧洲西岸高度场异常偏低、贝加尔湖西侧以气旋性环流为主、极地冷高压活跃时,有利于中高纬冷空气活跃南下,宁夏寒潮则偏多,反之则偏少。

Based on daily temperature observation data and reanalysis data of the geopotential height,sea level pressure,and wind field from 1961 to 2020,the characteristics of spatial and temporal change of cold waves,strong cold waves,and exceptionally strong cold waves lasting 24 h,48 h,and 72 h were studied in Ningxia over the past 60 years.The causes of atmospheric circulation anomalies of cold waves were also revealed.The results show the following:(1)In the past 60 years,cold waves of different intensities and different durations in Ningxia consistently showed the distribution characteristics of“shifting eastwards and northwards.”(2)The cumulative frequencies of cold waves,strong cold waves,and exceptionally strong cold waves in the region accounted for 71.7%,22.6%,and 5.7%of the total annual cold wave frequencies,respectively,among which cold waves dominated by process lasting 24 h and 48 h.The proportions of various durations for strong cold waves and exceptionally strong cold waves were equivalent.They mainly occured in October to April,during which the accumulated cold waves,strong cold waves,and exceptionally strong cold waves in the region accounted for 99%,98%,and 95%of those throughout the year,and there was a decreasing trend from January to April and increasing trend from October to December.(3)In the past 60 years,the cold waves,strong cold waves,and exceptionally strong cold waves have been decreasing at a rate of 4.5,2.8,and 0.18 per station every 10 years,respectively.Among them,the frequencies of waves of 24 h and 48 h as short durations were decreasing,but that of waves of 72 h as a long duration was decreasing.All types of cold waves decreased from the 1960s to the 1990s,reaching a minimum in the 1990s and increasing since the 2000s,with a sudden change around 1990.(4)Under the influence of global warming,the atmospheric circulation showed completely the opposite distribution characteristics between before and after the sudden change of cold waves in Ningxia.The key systems influencing cold waves in Ningxia are consistent.When the blocking high pressure in the Ural Mountains was stronger,the East Asian trough was deeper,the west Pacific subtropical high was weaker,the western side of Lake Baikal was dominated by cyclonic circulation,and cold high pressure at the ground was active,this was conducive to the southward movement of cold air in middle and high latitudes,and more cold waves in Ningxia.