  About 4000 exoplanets have been confirmed since the year of 1992, and for
most of the planets, the main parameters that can be measured are planetary
radius and mass. Based on these two parameters, surface gravity can be
estimated. In this work, we investigate the effects of varying radius and
gravity on the climate of rapidly rotating terrestrial planets with assuming
they have an ocean and Earth-like atmospheres (N$_2$, CO$_2$, and H$_2$O).
Using a three-dimensional (3D) atmospheric general circulation model (GCM), we
find that varying radius mainly influences the equator-to-pole surface
temperature difference while varying gravity mainly influences the mean surface
temperature. For planets of larger radii, the meridional atmospheric energy
transport is weaker, which warms the tropics but cools high latitudes. For
planets of larger gravities, the surface is globally cooler due to the fact
that saturated vapor pressure depends on air temperature only and column water
vapor mass is approximately equal to saturated vapor pressure over gravity
multiplied by relative humidity. The relative humidity does not change much in
our experiments. Ice albedo and water vapor feedbacks act to further amplify
the effects of varying radius and gravity. These results suggest that radius
and gravity are important factors for planetary climate, although they are not
as critical as stellar flux, atmospheric composition and mass, and rotation
rate. Future simulations are required to know how large the radius and gravity
could influence the width of the habitable zone using 3D GCMs.
