  Brown dwarfs and directly imaged exoplanets exhibit observational evidence
for active atmospheric circulation, raising critical questions about mechanisms
driving the circulation, its fundamental nature, and time variability. Our
previous work demonstrated the crucial role of cloud radiative feedback on
driving a vigorous atmospheric circulation using local models that assume a
Cartesian geometry and constant Coriolis parameters. In this study, we explore
the properties of the global dynamics. We show that, under relatively strong
dissipation in the bottom layers of the model, horizontally isotropic vortices
are prevalent at mid-to-high latitudes while large-scale zonally propagating
waves are dominant at low latitudes near the observable layers. The equatorial
waves have both eastward and westward phase speeds, and the eastward components
with typical speeds of a few hundred m/s usually dominate the equatorial time
variability. Lightcurves of the global simulations show variability with
amplitudes from 0.5 percent to a few percent depending on the rotation period
and viewing angle. The time evolution of simulated lightcurves is critically
affected by the equatorial waves, showing wave beating effects and differences
in the lightcurve periodicity to the intrinsic rotation period. The vertical
extent of clouds is the largest at the equator and decreases poleward due to
the increasing influence of rotation with increasing latitude. Under weaker
bottom dissipation, strong and broad zonal jets develop and modify wave
propagation and lightcurve variability. Our modeling results help to explain
the puzzling time evolution of observed lightcurves, a slightly shorter period
of variability in IR than in radio wavelengths, and the viewing angle
dependence of variability amplitude and IR colors.
