  We present a large ensemble of simulations of an Earth-like world with
increasing insolation and rotation rate. Unlike previous work utilizing
idealized aquaplanet configurations we focus our simulations on modern
Earth-like topography. The orbital period is the same as modern Earth, but with
zero obliquity and eccentricity. The atmosphere is 1 bar N$_{2}$-dominated with
CO$_{2}$=400 ppmv and CH$_{4}$=1 ppmv. The simulations include two types of
oceans; one without ocean heat transport (OHT) between grid cells as has been
commonly used in the exoplanet literature, while the other is a fully coupled
dynamic bathtub type ocean. The dynamical regime transitions that occur as day
length increases induce climate feedbacks producing cooler temperatures, first
via the reduction of water vapor with increasing rotation period despite
decreasing shortwave cooling by clouds, and then via decreasing water vapor and
increasing shortwave cloud cooling, except at the highest insolations.
Simulations without OHT are more sensitive to insolation changes for fast
rotations while slower rotations are relatively insensitive to ocean choice.
OHT runs with faster rotations tend to be similar with gyres transporting heat
poleward making them warmer than those without OHT. For slower rotations OHT is
directed equator-ward and no high latitude gyres are apparent. Uncertainties in
cloud parameterization preclude a precise determination of habitability but do
not affect robust aspects of exoplanet climate sensitivity. This is the first
paper in a series that will investigate aspects of habitability in the
simulations presented herein. The datasets from this study are opensource and
publicly available.
