中国冬季暖夜频率变化特征及其与海温的关系

采用排除台站迁移对逐日资料均一性影响的中国201个台站1960—2009年冬季逐日最低气温资料,NCEP/NCAR再分析的月平均500 h Pa位势高度场资料,及由NOAA重构的海温场资料,对中国冬季暖夜频率(frequence of warm winter night,FWWN)的时空变化特征及暖夜频率与全球海温的关系进行了分析。结果表明:近50 a中国冬季暖夜频率显著增加,并于1988年前后发生突变;冬季暖夜频率的变化幅度及趋势均是在西北地区东部最大,西南地区最小;中国冬季暖夜频率可以分为5个各自变化特征比较一致的区域;赤道印度洋到赤道西太平洋海区、黑潮区、北大西洋海区及南太平洋海区的海温指数均与中国冬季暖夜频率在全国大部分地区呈显著正相关;4个海区海温指数的异常年对应的大气环流场背景均能反映出它们分别与中国冬季暖夜频率呈正相关的事实。

Variation in the frequency of warm winter nights in China and the relationship with sea surface temperature

Based on the daily winter minimum temperature data of 201 Chinese meteorological stations,without the influence of station relocation,for the period 1960-2009,along with NCEP/NCAR monthly mean reanalysis data and NOAA reconstructed monthly mean sea surface temperature data,the spatial and temporal variation in the frequency of warm winter nights(FWWN) and the relationship with sea surface temperature(SST) and atmospheric circulation was studied.First,we ruled out the influence of the homogeneity generated by meteorological station relocation by using the t-test and multiple regression methods.Then,the FWWNs at the 201 stations in China were calculated.During 1960-2009,FWWN presents an increasing trend over most parts of China.The maximum values of the standard deviation and trend coefficient were located in Northwest China,while the minimum values lay in Southwest China.The first EOF mode''s spatial vector of FWWN produced an identical signal over the whole of China,indicating that there is an identical high winter warm night frequency abnormal or low frequency abnormal characteristic.The first EOF mode''s time coefficient indicates that FWWN increased during the 50-yr study period,and the mutation year of the first EOF time coefficient is 1988.In addition,FWWN shows obvious regional features,and can be divided into five consistent regions via the rotated EOF (REOF) method:(1)South China,Southeast China and Southwest China;(2)Central China and the east part of Southwest China;(3)Northeast China;(4)The east part of Northwest China,North China and East China;(5)The Xin Jiang area.Most of the regions'' FWWN showed an increasing trend,with the trend coefficients being statistically significant at the 0.05 level of reliability.Next,the relationship between FWWN and SST was analyzed.The Pacific Warm Pool SST index(I_PW),Kuroshio SST index(I>_Ks),North Atlantic SST index(I_NA) and South Pacific index(I_SP) showed significant positive correlation with FWWN,with their correlation coefficients passing the significance test over most parts of China.To examine the reason behind the relationship,the synthetic analysis method was used.The results showed that when the four SST indices were abnormal,the East Asian Trough intensity and Siberian High intensity were also abnormal.As the anomaly of the East Asian Trough intensity and Siberian High intensity can influence the cold air intensity,the four SST indexes therefore influenced the FWWN through their close relationship with the East Asian Trough intensity and Siberian High intensity.