Abstract
Tropical modes of variability, including the Madden‐Julian Oscillation
(MJO) and the El Niño‐Southern Oscillation (ENSO), are challenging to
represent in climate models. Previous studies suggest their fundamental
dependence on zonal asymmetry, but such dependence is rarely addressed
with fully coupled ocean dynamics. This study fills the gap by using
fully coupled, idealized Community Earth System Model (CESM) and
comparing two nominally ocean-covered configurations with and without a
meridional boundary. For the MJO-like intraseasonal mode, its separation
from equatorial Kelvin waves and the eastward propagation of its
convective and dynamic signals depend on the zonal gradient of the mean
state. For the ENSO-like interannual mode, in the absence of the ocean’s
meridional boundary, a circum-equatorial dominant mode emerges with
distinct ocean dynamics. The interpretation of the dependence of these
modes on zonal asymmetry is relevant to their representation in
realistic climate models.