Inter-annual And Inter-decadal Variations Of Extreme Minimum Temperature In China

Based on the data set of daily minimum temperature in China during1961-2010and NCEP/NCAR reanalysis data, by using harmonic analysis method and empiricalorthogonal function(EOF) analysis, Inter-annual(IA) and inter-decadal(ID) variationsof winter extreme minimum temperature (EMT) over the north and south of Chinadivided by35°N latitude line, are analyzed. Furthermore, circulation characteristicsand thermal forcing are particularly analyzed by using regression analysis. The mainconclusions are as following:Results show that the EMT frequency in the north and south of China both havequasi-biweekly climatological intraseasonal oscillation. In the north of China, thestrong cold air activities occurred in mid January, while at the end of December andJanuary in the south of China. The long-term trend of EMT frequency both in thenorth and south China are declining, and decreased more rapidly in the south China.For the north of China, the variance contribution between IA and ID components ofEMT frequency are almost equal, and ID component is a few stronger. While for thesouth of China, the IA component variance contribution accounts for more than halfof total variance. Further study shows that at ID time scales, the main mode of EMTfrequency shows variation in the north of China. While at IA time scales, the mainmode of EMT frequency represents a consistent variation in north Xinjiang area andthe south of China. Both the principal components of ID component and IAcomponent EOF mode show an amplitude abrupt transition in the1980s over the past49years.The North Atlantic Oscillation(NAO) changes from negative to positive phasewhen EMT frequency changes from positive to negative linearly in the north andsouth of China. At ID time scales (periods longer than8yr, the linear trend removed),the increased EMT frequency in the north of China is associated with the negative phase of Arctic oscillation(AO) in suface level pressure and the positive phase ofEurasian type in the500hPa geopotential height, with Ural blocking high and LakeBaikal through strengthening, and vice versa.The structure in the south of China bearsan overall resemblance with that in the north of China, but it is not significant. At IAtimes scales (periods less than8yr), as EMT frequency in the north of China is more,characterized by Lake Baikal trough strengthened and enhanced Siberian High andAleutian Low, associated with stationary wavenumber2structures. As EMTfrequency in the south of China is more, atmospheric circulation features astrengthened East Asian trough and positive anomalous sea level pressure overEurasia and the Atlantic Ocean, while the North American continent and the PacificOcean showing negative anomaly, closely related to a wavenumber1pattern.Further research shows that, the decline of EMT frequency both in the north andsouth of China is associated with global warming. The linear trend has a negativecorrelation with the sea surface temperature(SST) anomalies in the North Atlanticeand India ocean and can be preceded by melting of the marginal sea ice, especially inthe Greenland-Barents Sea ice during the preceding summer and autumn. For thenorth of China, its ID component may be affected by North Pacific SST anomalieswhich has a north-negative and south-positive distribution, and has a positivecorrelation with Greenland-Barents sea ice. While IA component has a significantnegative correlation with the SST anomalies along the west coast of North Americanand the anomalous SST between the subtropical North Pacific Ocean and the Gulf ofAlaska represents a distribution of the dipole oscillation. Also be affacted by the seaice melting in Chukchi Sea and the north sea area to new Svalbard islands. On theother hand, for the south of China, its ID componet, on which PDO has a remarkableinfluenced. It also has a negative correlation with the marginal sea ice except theGreenlands Sea and the Bering Sea. Beyond the IA time scale the SST anomalies overthe Bering Sea and the Gulf of Alaska prelude the anomalous winter EMT in the southof China. In addition, it also has a significant negative correlation with Pacific sectorsea ice.