A Comparison of Climates Simulated by a General Circulation Model when Run in the Annual Cycle and Perpetual Modes

Abstract

A comparison is made between the climate simulated by the Canadian Climate Centre (CCC) General Circulation Model when run its usual ?annual cycle?mode, in which the solar declination angle varies annually, and the climate which is simulated when the model is run in ?perpetual mode?, in which the solar declination angle is fixed. In particular, the annual cycle and perpetual mode January climates are compared as are the corresponding July climates. The comparison includes a global assessment of the significance of differences observed in mean sea level pressure, 500 mb height, lowest model level temperature, surface heat and evaporation fluxes, precipitation amounts, and zonal cross sections of temperature, zonal wind, and standing and transient eddy momentum transports. Clear and significant differences in climate between the annually forced and perpetually forced cases are observed. These changes are linked to differences in radiative heating and surface balances of energy and moisture.