  Rotation in planetary atmospheres plays an important role in regulating
atmospheric and oceanic heat flow, cloud formation and precipitation. Using the
Goddard Institute for Space Studies (GISS) three dimension General Circulation
Model (3D-GCM) we investigate how the effects of varying rotation rate and
increasing the incident stellar flux on a planet set bounds on a planet's
habitable zone with its parent star. From ensemble climate simulations we
identify which factors are the primary controllers of uncertainty in setting
these bounds. This is shown in particular for fully coupled ocean (FCO) runs --
some of the first that have been utilized in this context. Results with a Slab
Ocean (SO) of 100m mixed layer depth are compared with a similar study by Yang
et al. 2014, which demonstrates consistency across models. However, there are
clear differences for rotations rates of 1-16x present Earth sidereal day
lengths between the 100m SO and FCO models, which points to the necessity of
using FCOs whenever possible. The latter was recently demonstrated quite
clearly by Hu & Yang 2014 in their aquaworld study with a FCO when compared
with similar mixed layer ocean studies and by Cullum et al. 2014.
  We also show how these results have implications for Venus in the early
history of our Solar System since even at this time Venus received more solar
flux than Earth does today while it may still have had a slow retrograde
rotation. The Venus runs utilize a 2.9Gya solar spectrum generated with the
code of Claire et al. 2012, a modern Venus topography with an ocean filling the
lowlands (giving an equivalent depth of 310 meters if spread across the entire
surface), atmosphere of 1 bar N2, CO2=0.4mb, CH4=0.001mb and present day
orbital parameters, radius, & gravity. We demonstrate that ancient Venus could
have had quite moderate surface temperatures given these assumptions.
