Abstract
The National Center for Atmospheric Research (NCAR) Community Climate Model (CCM) and the Goddard Laboratory for Atmospheres (GLA) Climate Model (CM) differ from each other both in numerical structure and in forcing scheme. Since a proper simulation of atmospheric standing eddies in a numerical model is essential to long-range weather prediction and short-term climate forecast, it is important to explore the impact of these model difference on the simulation of standing eddies by contrasting their structure and energetics.
Several prominent differences are observed in the structures of standing eddies as simulated by the two models. In the middle and higher latitudes, the patterns of temperature and height anomalies depicting the standing eddies are more zonal in the NCAR CCM than in the GLA CM. At low latitudes, the structures of standing eddies in the two models have opposite phases in the eastern hemisphere. Furthermore, in the upper troposphere and lower stratosphere, the standing eddies of the GLA CM exhibit a second maximum amplitude which does not appear in the NCAR CCM. The differences in the treatment of forcing in the two models way result in them contrasts in the structure of standing eddies.
Energetics analysis is employed to explore the contrast between the physical processes maintaining the standing eddies in the two models. In the upper troposphere and lower stratosphere of the GLA CM, in addition to the second maximum amplitude of the standing eddies, the zonal mean westerlies in the middle latitudes increase monotonically with respect to height. Therefore, the interactions between standing eddies and the zonal mean state and between standing and transient eddies in both the thermal and the dynamic fields are significantly larger in the upper troposphere and lower stratosphere of the GLA CM. However, in the middle and lower troposphere of the GLA CM the conversion of available potential energy from the zonal mean state to support the standing eddies is not strong enough because of the insignificant meridional gradient of zonal mean temperature. The differences in the horizontal structures of standing eddies between the two models may be the cause of the smaller release of available potential energy in the GLA CM.
