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 ERA-Interim, 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.
