A Proposal for the Intercomparison of the Dynamical Cores of Atmospheric General Circulation Models

Abstract

A benchmark calculation is proposed for evaluating the dynamical cores of atmospheric general circulation models independently of the physical parameterizations. The test focuses on the long-term statistical properties of a fully developed general circulation; thus, it is particularly appropriate for intercomparing the dynamics used in climate models. To illustrate the use of this benchmark, two very different atmospheric dynamical cores-one spectral, one finite difference-are compared. It is found that the long-term statistics produced by the two models are very similar. Selected results from these calculations are presented to initiate the intercomparison.

Zonal Flow Regime Changes in a GCM and in a Simple Quasigeostrophic Model: The Role of Stratospheric Dynamics

“…4. In experiment C1, and only in C1, the dependence on DT of the maximum strength of the mass streamfunction is almost linear and thus agrees with the results of Held and Hou (1980), in spite of our imposing a reverse temperature gradient in the stratosphere. Three remarkable differences among the experiments are noticeable from Fig.…”

“…Wind speeds decrease away from this core, toward the pole and surface and, more rapidly, toward the equator and the stratosphere. This result conserves angular momentum, as in the Held and Hou (1980) theory of the axisymmetric circulation, albeit in the presence of a reversed stratospheric temperature gradient. The main shortcoming of this solution, though, is that no double jet is produced.…”

“…Its dynamical core is a global spectral model solving the primitive equations on sigma levels (Hoskins and Simmons 1975;James and Gray 1986). The diabatic heating rate is represented through Newtonian cooling and the dissipative processes by Rayleigh friction, which may act on each model level (see also Held and Suarez 1994). The model was run at a T21 resolution with 20 equally spaced s levels, following the analysis by Bordi et al (2007) on tropospheric double jets in Northern Hemisphere winter.…”

“…A reversed stratospheric meridional temperature gradient is set up and vertical diffusion is introduced to make the model simulation comparable with the Held and Hou (1980) analysis of nonlinear, axially symmetric circulations. The second experiment (C2) has the same meridional temperature gradient in the troposphere, whereas in the stratosphere it is set to zero.…”

*Parallel Computations in Problems of Climate Modeling

“…Extended by the idealized Held-Suarez forcing [2], the dynamics can be used for benchmarking purposes alone. It allows to switch between the explicit and semi-implicit time stepping scheme, as well as between direct and iterative solvers for the Helmholtz equation arising in the semi-implicit scheme, giving an opportunity for direct intercomparison of the methods at different grid resolutions.…”