How accurate did GCMs compute the insolation at TOA for AMIP-2?

Abstract

Monthly averages of solar radiation reaching the Top of the Atmosphere (TOA) as simulated by 20 General Circulation Models (GCMs) during the period 1985-1988 are compared. They were part of submissions to AMIP-2 (Atmospheric Model Intercomparison Project). Monthly averages of ISCCP-FD (International Satellite Cloud Climatology Project - Flux Data) are considered as reference. Considerable discrepancies are found: Most models reproduce the prescribed Total Solar Irradiance (TSI) value within ±0.7 Wm-2. Monthly zonal averages disagree between ±2 to ±7 Wm-2, depending on latitude and season. The largest model diversity occurs near polar regions. Some models display a zonally symmetric insolation, while others and ISCCP show longitudinal deviations of the order of ±1 Wm-2. With such differences in meridional gradients impacts in multiannual simulations cannot be excluded. Sensitivity studies are recommended. Copyright 2005 by the American Geophysical Union.