The JRA-55 Reanalysis: Representation of Atmospheric Circulation and Climate Variability

抄録

This study investigates the quality of the Japanese 55-year Reanalysis (JRA-55), which is the second global reanalysis constructed by the Japan Meteorological Agency (JMA), comparing with other reanalyses and observational datasets. Improvements were found in the representation of atmospheric circulation on the isentropic surface and in the consistency of momentum budget based on the mass-weighted isentropic zonal mean (MIM) method. The representation of climate variability in several regions was also examined. In the tropics, the frequencies of high spatial correlations with precipitation estimated using Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) are clearly higher in JRA-55 than in JRA-25. The results indicate that JRA-55 generally improved the representation of phenomena on a wide range of space–time scales, such as equatorial waves, and transient eddies in the storm track regions, compared with JRA-25 during the satellite era, and improved the temporal consistency compared with the older reanalyses throughout the reanalysis period. In the stratosphere, we found larger discrepancies between reanalyses for the extra-tropical stratosphere during the Southern Hemisphere (SH) winter. Comparisons with radiosonde temperature revealed that JRA-55 has a smaller bias in temperature than the other reanalyses in the extra-tropical SH winter before 1979. Some issues in JRA-55 were also identified. The amplitude of equatorial waves and the Madden–Julian oscillation (MJO) in JRA-55 is weaker than the other reanalyses. JRA-55 shows unrealistic strong cooling in South America and Australia, although the spatial distribution of the long-term temperature trends in JRA-55 is the closest to an observational dataset of global historical surface temperature.