Characteristics of the JRA-55 and ERA-interim datasets by using the three-dimensional normal mode energetics

Abstract

In this study, we conducted an energetics analysis of the atmospheric general circulation for up-to-date reanalyses, JRA-55 and ERA-Interim, and compared the result with that of the old reanalysis, JRA-25. Since three-dimensional normal mode functions are used, we can separate the energy spectrum into Rossby and gravity components. According to the comparison between JRA-55 and ERAInterim, it is found that the characteristics of the energy spectrum and the energy interaction are quite similar in zonal wavenumber and vertical mode domains. However, kinetic energy of Rossby modes for JRA-55 is larger than that for ERA-Interim in all wavenumbers. On the other hand, kinetic energy of gravity modes for JRA-55 is smaller than that for ERA-Interim in small wavenumbers. Therefore, one of the features of JRA-55 is that the wind and geopotential fields are close to the geostrophic balance. According to the comparison among JRA-55, ERA-Interim and JRA-25, the imbalance for JRA-55 at zonal wavenumbers 10 to 25 is similar to ERA-Interim and is smaller than that for JRA- 25. It is also found that the interactions of available potential energy in the zonal wavenumber domain for JRA-55 is comparable to that for ERA-Interim and is larger than that for JRA-25.