  We consider the atmospheric flow on short-period extra-solar planets through
two-dimensional numerical simulations of hydrodynamics with radiation transfer.
One side is always exposed to the irradiation from the host star. The other is
always in shadow. The temperature of the day side is determined by the
equilibrium which the planetary atmosphere establishes with stellar radiation.
Part of the thermal energy deposited on the day side is advected to the night
side by a current. The radiation transfer, the night-side temperature
distribution and by this the spectroscopic signature of the planet are
sensitive functions of the atmospheric opacity. If the atmosphere contains
grains with an abundanceand size distribution comparable to that of the
interstellar medium, shallow heating occurs on the day side and the night side
cools well below the day side. The temperature difference decreases as the
abundance of grains is reduced. A simple analytic model of the dissipation of
the circulation flow and associated kinetic heating is considered. This heating
effect occurs mostly near the photosphere, not deep enough to significantly
affect the size of planets. We show that the surface irradiation suppresses
convection near the photospheric region on the day side. In some cases
convection zones appear near the surface on the night side. This structural
modification may influence the response and dissipation of tidal disturbances
and alter the circularization and synchronization time scales.
