Using Atmospheric Budgets as a Constraint on Surface Fluxes

Possible methods for estimating surface fluxes include (i) use of bulk fluxes and in situ observations, (ii) use of model parameterizations to interpret specified inputs and compute surface fluxes, and (iii) various indirect methods, which rely on the fact that the mass and surface heat, energy, and momentum budgets must balance and so, given computations of all the other components in the various budget equations applied to fields either within the ocean or the atmosphere, fluxes may be inferred as a residual. This paper reviews the third approach using indirect methods and outlines the advantages associated with the use of global atmospheric analyses from four-dimensional data assimilation (4DDA). The time mean increment required in producing analyses in 4DDA is identical to the systematic short-term (6 h) assimilating model forecast error and is most likely due to errors in the model physics. Therefore, the analyses include a desirable fix, which allows the sum of the “physics” to be deduced from “dynamics.” The focus is on the heat and moisture budgets to infer surface heat fluxes and freshwater fluxes, but with the recognition of the need to balance the mass budget as well. The diurnal cycle of the vertically integrated mass budget for July 1985 and January 1996 from National Centers for Environmental Prediction (formerly the National Meteorological Center) reanalyses is presented, revealing the strong semidiurnal tide and highlighting the need for at least four-times-daily data. The new results reveal that gross violations of the mass budget continue to be present, but these can be allowed for. A discussion is given of other sources of errors contributing to the heat and moisture budgets.