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A comparison between two reanalysis datasets (the NCEP-NCAR and ERA-40 reanalyses) is conducted over East Eurasia. The summer sea level pressure (SLP) from these datasets are specifically compared in the two periods from 1960 to 1979, and 1980 to 1999 in order to examine the long-term homogeneity and reliability of these datasets. The SLP of the NCEP-NCAR over Mongolia and its vicinity exhibits an obvious increase between the two periods, but it is not recognized in the ERA-40. This discrepancy is mainly due to sudden increases in the SLP around Mongolia in the mid-1960s and mid-1970s in the NCEP-NCAR, which are not recognized in the ERA-40. Other observational datasets used in this study show similar variations to those appeared in the ERA-40. It is likely that the sudden increases in SLP observed in the NCEP-NCAR before the 1970s are spurious, and this result implies that the NCEPNCAR reanalysis over Mongolia and its vicinity before the 1970s does not reproduce the actual surface conditions. The ERA-40 may also have some problems such as the lower SLP than that of the observational data before the 1980s, but the difference is, in general, less than 3 hPa and this value is smaller than that recognized between the NCEP-NCAR and the observational data before the mid- 1970s. Therefore, it seems that the ERA-40 is more accurate, and is more appropriate to use than the NCEP-NCAR, for the moment, in investigations of the interdecadal climate change in the late 1970s over East Eurasia. However, care must also be taken into the above-mentioned problems.

NOTES AND CORRESPONDENCE A Comparison of Summer Sea Level Pressure over East Eurasia between NCEP-NCAR Reanalysis and ERA-40 for the Period 1960-99