Regional Earth-Atmosphere Energy Balance Estimates Based on Assimilations with a GCM

Michael A. Alexander, Dept. of Meteorology, University of Wisconsin, Madison, WI

Siegfried D. Schubert, GSFC, NASA, Greenbelt, MD


The column budget technique described by Oort and Vonder Haar (1976) is used to assess the physical consistency and accuracy of estimates of the earth-atmosphere energy balance. Regional estimates of the atmospheric budget terms, the net radiation at the top of the atmosphere, and the time tendency and flux divergence of energy are calculated for the Special Observing Periods of the FGGE year. The data are assimilated by the Goddard Laboratory for the Atmospheres (GLA) four-dimensional analysis system. Ocean heat storage is obtained from marine temperature records while the energy flux through the surface and ocean heat flux divergence are computed as residuals.

During winter the midlatitude oceans supply large quantities of energy to the overlying atmosphere which then transports the energy to the continental and polar heat sinks; the energy flows in the opposite direction during summer. The energy exchange between continental and oceanic regions is much stronger in the Northern Hemisphere where the land coverage and land-sea differences are greater.

The uncertainties in the energy balance calculations are assessed by examining the errors in the observations, the data assimilation system including the GLA general circulation model, and the energy budget procedures. Sensitivity tests, error analyses and comparison with other studies indicate that the uncertainties in the continental scale atmospheric energy flux divergence and the surface energy flux are approximately 20 W m-2 and 30 W m-2, respectively. We conclude that at present it is not possible to estimate accurately the ocean heat divergence and transport using the column budget technique.