Comparative terrestrial atmospheric circulation regimes in simplified global circulation models. Part II: Energy budgets and spectral transfers

The energetics of possible global atmospheric circulation patterns in an Earth‐like atmosphere are explored using a simplified global General Circulation Model (GCM) based on the University of Hamburg's Portable University Model for the Atmosphere (designated here as PUMA‐S), forced by linear relaxation towards a prescribed temperature field and subject to Rayleigh surface drag and hyperdiffusive dissipation. Results from a series of simulations, obtained by varying planetary rotation rate Ω with an imposed equator‐to‐pole temperature difference, were analysed to determine the structure and magnitude of the heat transport and other contributions to the energy budget for the time‐averaged, equilibrated flow. These show clear trends with rotation rate, with the most intense Lorenz energy cycle for an Earth‐sized planet occurring with a rotation rate around half that of the present‐day Earth (i.e., Ω∗ = Ω/Ω E = 1/2, where Ω E is the rotation rate of the Earth). Kinetic energy (KE) and available potential energy (APE) spectra, E K (n) and E A (n) (where n is total spherical wavenumber), also show clear trends with rotation rate, with n −3 enstrophy‐dominated spectra around Ω∗ = 1 and steeper (∼n −5) slopes in the zonal mean flow with little evidence for the n −5/3 spectrum anticipated for an inverse KE cascade. Instead, both KE and APE spectra become almost flat at scales larger than the internal Rossby radius, L d , and exhibit near‐equipartition at high wavenumbers. At Ω∗