Comparative energetics of ERA-40, JRA-25 and NCEP-R2 reanalysis, in the wave number domain

Abstract

TheEuropeanCentreforMedium-RangeWeatherForecasts40-year Reanalysis (ERA-40), the Japan Meteorological Agency and Central Research Institute of Electric Power Industry 25-year Reanalysis (JRA-25), and the National Centers for Environmental Prediction andDepartmentofEnergyAMIP-IIReanalysis(NCEP-R2)areintercompared through a global energetics analysis for all seasons. Overall, the Lorenz energy cycle is consistent among the three datasets. The flow of energy and the peaks and slopes in the spectra of the various components agree between the three reanalysis. Additionally, the temporal variability of the energy cycle terms shows consistency between the three reanalysis. Most differences between the three reanalysis are related to the magnitudes of energy forms and energy conversion/transfer rates at each wave number, generally following the relation ERA−40 > JRA−25 > NCEP−R2, and mainly located in the Southern Hemisphere. The best agreement between the three datasets is found for northern winter. Differences between the three datasets are greater for the otherseasons,beinggreatestfornorthernsummer.Ingeneral,these discrepancies are fairly modest, being likely due to the different model biases and resolutions, and the different data assimilation methods used by the respective reanalysis systems. The energetics of the three reanalysis become closer to each other in more recent years, which is likely due to the increase in the number of observations assimilated in the reanalysis.