Assessment of Energy Budget in Weather Forecasting General Circulation Models

Abstract

A comprehensive data set, which has been archived during Enhanced Observing Period 3 (EOP3-from 1 October 2002 to 30 September 2003) of the Coordinated Enhanced Observing Period, is used to assess the representation of surface energy budget in five operational weather forecasting General Circulation Models (GCMs). It is found that shortwave downward radiation is generally over-estimated and downward longwave radiation is under-estimated. Since the error in shortwave downward radiation is dominant in most of the models, net radiation is over-estimated in all the models. Turbulent heat fluxes are not well modeled by all the GCMs and there are systematical errors that might be attributed to incorrect model parameter setting or model physics. The GCMs generally over-predict nighttime downward sensible heat fluxes but under-predict diurnal ranges of surface-air temperature difference, showing that heat transfer resistances are under-predicted. This problem is especially severe for arid and semi-arid regions. Also, a model without explicit representation of vegetation processes is not able to reproduce observed surface energy budget.