Abstract
Idealized models can reveal insights into Earth’s climate system by
reducing its complexities. However, their potential is undermined by the
scarcity of fully coupled idealized models with components comparable to
contemporary, comprehensive Earth System Models. To fill this gap, we
compare and contrast the climates of two idealized planets which build
on the Simpler Models initiative of the Community Earth System Model
(CESM). Using the fully coupled CESM, the Aqua configuration is
ocean-covered except for two polar land caps, and the Ridge
configuration has an additional pole-to-pole grid-cell-wide continent.
Contrary to most sea surface temperature profiles assumed for
atmosphere-only aquaplanet experiments with the thermal maximum on the
equator, the coupled Aqua configuration is characterized by a global
cold belt of wind-driven equatorial upwelling, analogous to the eastern
Pacific cold tongue. The presence of the meridional boundary on Ridge
introduces zonal asymmetry in thermal and circulation features, similar
to the contrast between western and eastern Pacific. This zonal
asymmetry leads to a distinct climate state from Aqua, cooled by
~2{degree sign}C via the radiative feedback of clouds
and water vapor. The meridional boundary of Ridge is also crucial for
producing a more Earth-like climate state compared to Aqua, including
features of atmospheric and ocean circulation, the seasonal cycle of the
Intertropical Convergence Zone, and the meridional heat transport. The
mean climates of these two basic configurations provide a baseline for
exploring other idealized ocean geometries, and their application for
investigating various features and scale interactions in the coupled
climate system.