对东亚北部(40—50°N,100—130°E)区域1953—2012年大气温度的冬季-夏季-次年冬季(简称冬季-冬季)的季节变化特征进行了初步研究.结果表明:2008年以来,该区域的气温从低层至高层(1000—400 h Pa)连续三年出现冬季偏冷-夏季偏暖-次年冬季偏冷的典型特征,20世纪50—60年代亦有类似情况;而20世纪90年代则出现了与此相反的冬季偏暖-夏季偏冷-次年冬季偏暖的变化特征.将这种典型的气温季节变化特征定义为一种新的变化机理:冬季-冬季再现(WWR).根据1953—2012年的历年变化情况将这60年划分为四种不同的类型:负(正)冬季-冬季再现(negative/positive WWR)型和负(正)冬季-冬季非再现(negative/positive non-WWR)型.其中,气温表现为WWR型的年份共计23年,出现概率近40%,并且该WWR特征是相对独立于El Nio-南方涛动指数的变化而存在的.对不同类型年份的位势高度场、垂直速度场及其850 h Pa风场进行的合成分析表明:对于WWR型,高层(500 h Pa)至低层(1000 h Pa)的大气内部动力过程具有与气温相匹配的冬季-冬季的再现特征;而non-WWR型则没有出现类似的特征,从而在一定程度验证了WWR存在的可能性.WWR的提出为进一步开展当前全球增暖背景下冬季低温事件的频发提供了一个新的思路.
This paper systematically evaluates the deviations that appear in the hindcasts of the East Asian summer precipitation（EASP） decadal change in the late 1990 s in two global coupled models（BCC-CGCM and BCC-CSM）.The possible causes for the deviations between the model hindcasts and observations are analyzed.The results show that the hindcasts of EASP by BCC-CGCM and BCC-CSM deviate from observations,with the anomaly correlation coefficient（ACC） being-0.01 and-0.09 for the two models,respectively.The SST anomalies in North and West Pacific and the SST index values predicted by the two models also deviate from the observations,indicating that inconsistent SST fields may be the key factor leading to the deviation in the prediction of the EASP decadal shift.Thus,a dynamic-analogue scheme is proposed to correct the precipitation hindcasts by using SSTs,where SST and EASP are highly correlated,to select historical analogue cases.Cross validations show that the average ACC of the temporal-latitude distribution of the EASP between the corrected hindcasts and observations is 0.18 for BCC-CGCM and0.02 for BCC-CSM;both are much higher than the uncorrected hindcasts.Applying the dynamic-analogue correction scheme in both models successfully improves prediction of the EASP decadal change in the late1990 s.
Based on an objective identification technique for regional low temperature event（OITRLTE）, the daily minimum temperature in China has been detected from 1960 to 2013. During this period, there were 60 regional extreme low temperature events（ERLTEs）, which are included in the 690 regional low temperature events（RLTEs）. The 60 ERLTEs are analyzed in this paper. The results show that in the last 50 years, the intensity of the ERLTEs has become weak; the number of lasted days has decreased; and, the affected area has become small. However, that situation has changed in this century.In terms of spatial distribution, the high intensity regions are mainly in Northern China while the high frequency regions concentrate in Central and Eastern China. According to the affected area of each event, the 60 ERLTEs are classified into six types. The atmospheric circulation background fields which correspond to these types are also analyzed. The results show that, influenced by stronger blocking highs of Ural and Lake Baikal, as well as stronger southward polar vortex and East Asia major trough at 500-h Pa geopotential height, cold air from high latitudes is guided to move southward and abnormal northerly winds at 850 h Pa makes the cold air blow into China along diverse paths, thereby forming different types of regional extreme low temperatures in winter.
