Abstract
Eight current re-analyses—NCEP/NCAR Re-analysis (NCEPI), NCEP/DOE Re-analysis (NCEPII), NCEP Climate Forecast System Re-analysis (CFSR), ECMWF Interim Re-analysis (ERA-Interim), Japanese 55-year Re-analysis (JRA-55), NASA Modern-Era Retrospective Analysis for Research and Applications (MERRA), NOAA Twentieth Century Re-analysis (20CR), and ECMWF’s first atmospheric re-analysis of the 20th century (ERA-20C)—are assessed to clarify their quality in capturing the East Asian summer monsoon (EASM) rainfall structure and its associated general circulation. They are found to present similar rainfall structures in East Asia, whereas they illustrate some differences in rainfall intensity, especially at lower latitudes. The third generation of re-analysis shows a better estimate of rainfall structure than that in the first and extended generation of re-analysis. Given the fact that the rainfall is ingested by the data assimilation system, the re-analysis cannot improve its production of rainfall quality. The mean sea level pressure is generated by re-analysis, showing a significant uncertainty over the Tibetan Plateau and its surrounding area. In that region, the JRA-55 and MERRA have a negative bias (BIAS), while the other six re-analyses present a positive BIAS to the observed mean sea level pressure. The 20CR and the ERA-20C are ancillary datasets to analyse the EASM due to the fact that they only apply limit observations into the data assimilation system. These two re-analyses demonstrate a prominent difference from the observed winds in the upper-air. Although the upper level winds exhibit difference, the EASM index is consistent in the eight re-analyses, which are based upon the zonal wind over 850 hPa.
Highlights
The East Asian summer monsoon (EASM) is an important part of the global climate system and plays a vital role in the Asian climate
They are the first generation of re-analysis (NCEPI and NCEPII), the third generation of re-analysis (CFSR, ERA-Interim, Modern-Era Retrospective Analysis for Research and Applications (MERRA), and JRA-55), and the extended-generation re-analysis (20CR and ERA-20C)
It is worth mentioning that JRA-55 is the best re-analysis dataset in capturing the pattern distribution monsoon rainfall structure, but it demonstrates the worst performance in representing the amplitude of monsoon rainfall structure, but it demonstrates the worst performance in representing the of rainfall, due to its having the largest root-mean-square error (RMSE) (1.44)
Summary
The East Asian summer monsoon (EASM) is an important part of the global climate system and plays a vital role in the Asian climate. Developed a new-generation re-analysis to provide a long time cover observational validation dataset to assess climate model simulations of the 20th century, the ECMWF’s first atmospheric re-analysis of the 20th century (ERA-20C; [16]) and the Twentieth Century Reanalysis v2 (20CR; [17]), respectively. Because the zonal and meridional wind, as well as geopotential height, are directly assimilated from observational data, they are the most reliable variable in the first-, second- and third-generation re-analyses. These data are categorised as “A” variables. Pressure level variables (e.g., wind fields and geopotential height) in extended generation reanalysis is classified as “C” class These variables should be compared to observational data when they are used for scientific research, especially for studying the EASM.
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