Intercomparison of the Summertime Subtropical High from the ERA-40 and NCEP/NCAR Reanalysis over East Eurasia and the western North Pacific

An intercomparison of summertime (JJA) subtropical geopotential heights from the ERA-40 and NCEP/NCARreanalysis is specifically conducted over East Eurasia and the western North Pacific. The NCEP/NCAR is obviouslylower than the ERA-40 in the mid-to-lower troposphere in most regions of East Eurasia before the mid-1970s, butbecomes higher than the ERA-40 after the mid-1970s and thus demonstrates stronger increased trends during theperiod of 1958--2001. Both reanalyses are lower than the observations in most regions of China. The NCEP/NCARespecially shows tremendously systematic lower values before the mid-1960s and displays abrupt changes beforethe 1970s. Several indices of the western North Pacific subtropical high (WNPSH), calculated from both reanalyzedsummer geopotential heights, also reveal that the variation trend of the NCEP/NCAR is stronger than that of theERA-40 in the mid-to-lower troposphere from 1958 to 2001. Through singular value decomposition (SVD) analysis,the summer geopotential heights at 500 hPa from the ERA-40 are better than the NCEP/NCAR counterparts atinteracting with the precipitation over the East Asian monsoon region. The results indicate that the NCEP/NCARin the mid-and-lower troposphere may overestimate interdecadal changes and should be used cautiously to studythe relationship between the WNPSH and precipitation ove ther East Asia Monsoon region before the mid-1970s.