  The response of the general circulation in a dry atmosphere to various
atmospheric shortwave absorptivities is investigated in a three-dimensional
general circulation model with grey radiation. Shortwave absorption in the
atmosphere reduces the incoming radiation reaching the surface but warms the
upper atmosphere, significantly shifting the habitable zone toward the star.
The strong stratification under high shortwave absorptivity suppresses the
Hadley cell in a manner that matches previous Hadley cell scalings. General
circulation changes may be observable through cloud coverage and superrotation.
The equatorial superrotation in the upper atmosphere strengthens with the
shortwave opacity, as predicted based on the gradient wind of the
radiative-convective equilibrium profile. There is a sudden drop of equatorial
superrotation at very low shortwave opacity. This is because the Hadley cell in
those cases are strong enough to fill the entire troposphere with zero momentum
air from the surface. A diurnal cycle (westward motion of substellar point
relative to the planet) leads to acceleration of the equatorial westerlies in
general, through the enhancement of the equatorward eddy momentum transport,
but the response is not completely monotonic, perhaps due to the resonance of
tropical waves and the diurnal forcing.
