We present three-dimensional atmospheric circulation models of GJ 1214b, a
2.7 Earth-radius, 6.5 Earth-mass super Earth detected by the MEarth survey.
Here we explore the planet's circulation as a function of atmospheric
metallicity and atmospheric composition, modeling atmospheres with a low
mean-molecular weight (i.e., H2-dominated) and a high mean-molecular weight
(i.e. water- and CO2-dominated). We find that atmospheres with a low
mean-molecular weight have strong day-night temperature variations at pressures
above the infrared photosphere that lead to equatorial superrotation. For these
atmospheres, the enhancement of atmospheric opacities with increasing
metallicity lead to shallower atmospheric heating, larger day-night temperature
variations and hence stronger superrotation. In comparison, atmospheres with a
high mean-molecular weight have larger day-night and equator-to-pole
temperature variations than low mean-molecular weight atmospheres, but
differences in opacity structure and energy budget lead to differences in jet
structure. The circulation of a water-dominated atmosphere is dominated by
equatorial superrotation, while the circulation of a CO2-dominated atmosphere
is instead dominated by high-latitude jets. By comparing emergent flux spectra
and lightcurves for 50x solar and water-dominated compositions, we show that
observations in emission can break the degeneracy in determining the
atmospheric composition of GJ 1214b. The variation in opacity with wavelength
for the water-dominated atmosphere leads to large phase variations within water
bands and small phase variations outside of water bands. The 50x solar
atmosphere, however, yields small variations within water bands and large phase
variations at other characteristic wavelengths. These observations would be
much less sensitive to clouds, condensates, and hazes than transit
observations.Comment: 12 pages, 11 figures, 2 tables, accepted to Ap
