  Exoplanets on eccentric orbits experience an incident stellar flux that can
be markedly larger at periastron versus apoastron. This variation in
instellation can lead to dramatic changes in atmospheric structure in regions
of the atmosphere where the radiative and advective heating/cooling timescales
are shorter than the orbital timescale. To explore this phenomenon, we develop
a sophisticated one-dimensional (vertical) time-stepping atmospheric structure
code, EGP+, capable of simulating the dynamic response of atmospheric thermal
and chemical structure to time-dependent perturbations. Critically, EGP+ can
efficiently simulate multiple orbits of a planet, thereby providing new
opportunities for exoplanet modeling without the need for more
computationally-expensive models. We make the simplifying assumption of
cloud-free atmospheres, and apply our model to HAT-P-2b, HD~17156b, and
HD~80606b, which are known to be on higher-eccentricity orbits. We find that
for those planets which have Spitzer observations, our planet-to-star ratio
predictions are roughly consistent with observations. However, we are unable to
reproduce the observed peak offsets from periastron passage. Finally, we
discuss promising pathways forward for adding new model complexity that would
enable more detailed studies of clear and cloudy eccentric planets as well as
worlds orbiting active host stars.
