The ongoing characterization of hot Jupiters has motivated a variety of
circulation models of their atmospheres. Such models must be integrated
starting from an assumed initial state, which is typically taken to be a
wind-free, rest state. Here, we investigate the sensitivity of hot-Jupiter
atmospheric circulation models to initial conditions. We consider two classes
of models--shallow-water models, which have proven successful at illuminating
the dynamical mechanisms at play on these planets, and full three-dimensional
models similar to those being explored in the literature. Models are
initialized with zonal jets, and we explore a variety of different initial jet
profiles. We demonstrate that, in both classes of models, the final,
equilibrated state is independent of initial condition--as long as frictional
drag near the bottom of the domain and/or interaction with a specified
planetary interior are included so that the atmosphere can adjust angular
momentum over time relative to the interior. When such mechanisms are included,
otherwise identical models initialized with vastly different initial conditions
all converge to the same statistical steady state. In some cases, the models
exhibit modest time variability; this variability results in random
fluctuations about the statistical steady state, but we emphasize that, even in
these cases, the statistical steady state itself does not depend on initial
conditions. Although the outcome of hot-Jupiter circulation models depend on
details of the radiative forcing and frictional drag, aspects of which remain
uncertain, we conclude that the specification of initial conditions is not a
source of uncertainty, at least over the parameter range explored in most
current models.Comment: Revised version; accepted and published. 16 pages, 16 figure
