The atmospheric energy budget and implications for surface fluxes and ocean heat transports

Comprehensive diagnostic comparisons and evaluations have been carried out with the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) and European Centre for Medium Range Weath er Forecasts (ECMWF) reanalyses of the vertically integrated atmospheric en ergy budgets. For 1979 to 1993 the focus is on the monthly means of the div ergence of the atmospheric energy transports. For February 1985 to April 19 89, when there are reliable top-of-the-atmosphere (TOA) radiation data from the Earth Radiation Budget Experiment (ERBE), the implied monthly mean sur face fluxes are derived and compared with those from the assimilating model s and from the Comprehensive Ocean Atmosphere Data Set (COADS), both locall y and zonally integrated, to deduce the implied ocean meridional heat trans ports. While broadscale aspects and some details of both the divergence of atmosph eric energy and the surface flux climatological means are reproducible, esp ecially in the zonal means, differences are also readily apparent. Systemat ic differences are typically similar to 20 W m(-2). The evaluation highligh ts the poor results over land. Land imbalances indicate local errors in the divergence of the atmospheric energy transports for monthly means on scale s of similar to 50 km (T31) of 30 W m(-2) in both reanalyses and similar to 50 W m(-2) in areas of high topography and over Antarctica for NCEP/NCAR. Over the oceans in the extratropics, the monthly mean anomaly time series o f the vertically integrated total energy divergence from the two reanalyses correspond reasonably well, with correlations exceeding 0.7. A common mont hly mean climate signal of about 40 W m(-2) is inferred along with local er rors of 25 to 30 W m(-2) in most extratropical regions. Except for large scales, there is no useful common signal in the tropics. a nd reproducibility is especially poor in regions of active convection and w here stratocumulus prevails. Although time series of monthly anomalies of s urface bulk flu?;es from the two models and GOADS agree very well over the northern extratropical oceans, the total fields all contain large systemati c biases which make them unsuitable for determining ocean heat transports. TOA biases in absorbed shortwave, outgoing longwave and net radiation From both reanalysis models are substantial (>20 W m(-2) in the tropics) and ind icate that clouds are a primary source of problems in the model fluxes. bot h at the surface and the TOA. Time series of monthly GOADS surface fluxes a re shown to be unreliable south of about 20 degreesN where there are fewer than 25 observations per 5 degrees square per month. Only the derived surfa ce fluxes give reasonable implied meridional ocean heat transports.