  The energetics of possible global atmospheric circulation patterns in an
Earth-like atmosphere are explored using a simplified GCM based on the
University of Hamburg's Portable University Model for the Atmosphere. Results
from a series of simulations, obtained by varying planetary rotation rate
{\Omega} with an imposed equator-to-pole temperature difference, were analysed
to determine the heat transport and other contributions to the energy budget
for the time-averaged, equilibrated flow. These show clear trends with
{\Omega}, 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. KE
and APE spectra, E_K(n) and E_A(n) (where n is total spherical wavenumber),
also show clear trends with \Omega, with n^{-3} enstrophy-dominated spectra
around \Omega* = \Omega/\Omega_E = 1, where \Omega_E is the rotation rate of
the Earth) and steeper (\sim 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 \Omega* << 1, the spectrum becomes dominated by KE with E_K(n)
\sim 2-3 E_A(n) at most wavenumbers and a slope \sim n^{-5/3} across most of
the spectrum. Spectral flux calculations show that enstrophy and APE are almost
always cascaded downscale, regardless of {\Omega}. KE cascades are more
complicated, however, with downscale transfers across almost all wavenumbers,
dominated by horizontally divergent modes, for \Omega* \lesssim 1/4. At higher
rotation rates, transfers of KE become increasingly dominated by rotational
components with strong upscale transfers (dominated by eddy-zonal flow
interactions) for scales larger than L_d and weaker downscale transfers for
scales smaller than L_d.
