Atmospheric Energy Budgets in the Japanese Reanalysis: Evaluation and Variability

Abstract

579 IntroductionA continuing interest is to document the flow of energy through the climate system for the annual mean, its annual cycle and its variability. The main focus of our work has been on the bulk vertically-integrated atmospheric energy budget (Trenberth et al. 2001; Stepaniak 2003a, b, 2004) and especially the role of water (Trenberth et al. 2007). The main datasets required are the full atmospheric analyses of all the state variables every 6 hours to enable the computation of various energy forms (internal energy, sensible heat, latent energy, potential energy, dry static energy, moist static energy, and kinetic energy), the storage and changes in storage (tendency) of these components, and their transports and divergences. In the past we have made extensive use of reanalyses from National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) (referred to as NRA) (Kalnay et al. 1996) and the European Centre for Medium Range Weather Forecasts (ECMWF), known as ERA-40 (Uppala et al. 2005). In this paper we report on results for the recent Japanese Reanalysis (JRA) (Onogi et al. 2007) starting in 1979.Use is made of top-of-atmosphere (TOA) observed radiative fluxes from satellite measurements and computed surface fluxes into land or ocean to evaluate how well the energy budget can Journal of the Meteorological Society of Japan, Vol. 86, No. 5, pp. 579−592, 2008 Atmospheric Energy Budgets in the Japanese Reanalysis: AbstractThe vertically-integrated atmospheric energy and moisture budgets have been computed for all available months for the Japanese reanalysis (1979 to 2004), and results are described in detail for the month of January 1989 and compared with those of other reanalyses. Time series are also presented. The moistening, diabatic heating and total energy forcing of the atmosphere are computed as a residual from the analyses using the moisture, dry energy (dry static energy plus kinetic energy) and total atmospheric (moist static plus kinetic) energy budget equations. These fields are also computed from the model output based on the assimilating model parameterizations. Moreover, some component fields can also be computed from observations to evaluate the results. In particular, when the vertically-integrated forcings computed from the model parameterizations are compared with available observations and the budget-derived values, significant JRA model biases are revealed in radiation and precipitation. The energy and moisture budgetderived quantities are more realistic than the model output and better depict the real atmosphere. However, low frequency decadal variability is spurious and is mainly associated with changes in the observing system. Results also depend on the quality of the analyses which are not constructed to conserve mass, moisture or energy, owing to analysis increments. Although there has been considerable progress in depicting the diabatic components of the atmosphere, some problems remain, and suggestions are made on where research can...

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