Planetary Albedo Partitioning of Earth-Like Exoplanets with Variations in Rotation Periods and Obliquity

Previous studies using satellite data show that modern day Earth's planetary albedo is largely driven by atmospheric scattering and the contributions from both hemispheres towards the planetary albedo is nearly balanced (Stephens, 2015, Rev Geo). The planetary albedo can be partitioned into atmospheric and surface contributions using a single layer atmosphere model (Donohoe and Battisti, 2011, J. Clim). Though both hemispheres have remarkably different magnitudes in surface albedo, partitioning the planetary albedo reveals that the atmospheric contribution asymmetry in the southern hemisphere cancels the surface contribution asymmetry in the northern hemisphere. This cancellation comes from the northern hemisphere containing more land mass (corresponding to a larger surface contribution) and the southern hemisphere containing more clouds (corresponding to a larger atmospheric contribution). Studies suggests that clouds dominate the atmospheric scattering contribution while masking the underlying surface albedo and that the atmosphere attenuates the surface contribution by a factor of three (Donohoe and Battisti, 2011, J. Clim).

The purpose of this research is to apply the same albedo partitioning to a set of simulations (70 total) from a three-dimensional global climate model (ROCKE-3D, Way 2018, ApJ Suppl.) of Earth-like exoplanets with variations in rotation period (1-128 days) and obliquity (0 ° - 90°) (He, 2022, ApJ). As an example of the ROCKE-3D data, planetary albedo for all 70 simulation runs is displayed in the below figure. Investigating the albedo partitioning and hemispheric differences reveals how different insolation patterns modify the surface and atmospheric contributions to planetary albedo in Earth-like climates. Additional analyses of the complete planetary energy budget terms (including thermal radiation and energy transports) show how the planetary albedo changes are coupled to different responses in the simulated climates.