ON THE UNCERTAINTY IN ESTIMATES OF ATMOSPHERIC HEATING DUE TO DATA POSTPROCESSING

Using a general circulation model (GCM) dataset, the impact of postpro cessing interpolation from model sigma to pressure coordinates on a di agnostic analysis of the atmospheric energy balance is examined. Vario us isobaric resolutions are chosen that correspond to those provided i n existing analysis archives generated by the National Meteorological Center and the European Centre for Medium-Range Weather Forecasts. Lar ge differences are found between diabatic heating computed residually in isobaric coordinates versus sigma coordinates. Vertically averaged heating reconstructed from pressure level circulation data is found to be in error locally by 10%-50%, with poorer results occurring at coar ser vertical resolution. For the zonally averaged isobaric heat balanc e, the error exceeds the total zonally averaged heating near the tropo pause and near the surface. In the former region, the heating is quite small, whereas in the latter region it exceeds 1 K day-1. In contrast , reconstructing the heat balance directly from the GCM sigma-level ci rculation data introduces errors generally less than 5% of the model's explicit heating. Although uncertainties exist in our results stemmin g from the use of a single GCM dataset and a particular vertical inter polation method, they suggest the importance of performing analyses on an assimilating model's coordinate surfaces for the purpose of quanti tative climate monitoring.