Baroclinic Jets on Other Jupiters and Earths
Abstract
Dynamics of baroclinic jets on extrasolar planets is studied using three-dimensional
general circulation models (GCMs) which solve the traditional hydrostatic primitive
equations. The focus is on: i ) baroclinic
ow and instability on hot-Jupiters; ii )
detailed GCM intercomparison in a commonly used extrasolar planet setup; and,
iii ) equatorial superrotation on Earth-like planets.
Stability, non-linear evolution and equilibration of high-speed ageostrophic jets are
studied under adiabatic condition relevant to hot-Jupiters. It is found that zonal jets
can be baroclinically unstable, despite the planetary size of the Rossby deformation
scale, and that high resolution is necessary to capture the process. Non-linear jet
evolution is then used as a test case to assess model convergence in ve GCMs
used in current hot-Jupiter simulations. The GCMs are also tested under a diabatic
condition (thermal relaxation on a short timescale) similar to that used in many
hot-Jupiter studies. In the latter case, in particular, the models show signi cant
inter- and intra-model variability, limiting their quantitative prediction capability.
Some models severely violate global angular momentum conservation.
The generation of equatorial superrotation in Earth-like atmospheres, subject
to \Held & Suarez-like" zonally-symmetric thermal forcing is also studied. It is
shown that transition to superrotation occurs when the meridional gradient of the
equilibrium surface entropy is weak in this setup. Two factors contribute to the
onset of superrotation | suppression of breaking Rossby waves (generated by midlatitude
baroclinic instability) that decelerate the equatorial
ow, and, generation of
inertial and barotropic instabilities in the equatorial region that provide the stirring
to accelerate the equatorial
ow.
In summary, forcing condition and physical setup used in current hot-Jupiter
simulations severely stretch model performance and predictive capability. Superrotation
in Earth-like conditions may be common, but its strength decreases with
resolution. Broadly, numerical convergence must be assessed in GCM experiments
for each problem or setup considered.
Authors
Polichtchouk, InnaCollections
- Theses [3919]