Atmospheric Energy Budgets in the Japanese Reanalysis: Evaluation and Variability

Abstract

The 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 budget-derived 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 make further improvements.