Understanding the Dynamics of the Cloud-Level Atmosphere on Venus and
Venus Analog Exoplanets Using a Middle Atmosphere General Circulation
Model
Abstract
Venus is comparable to the Earth in size and overall distance from the
Sun, but is outside of a defined “habitable zone” in which water can
exist in liquid form. The deep atmosphere of Venus provides a hostile
environment for life. However, recent work suggests that the atmosphere
at cloud altitudes, which includes regions with temperatures and
pressures similar to those at the Earth’s surface, could provide
possible locations for microscopic life. Since the transit method
strongly favors observations of planets close to their host stars, Venus
analogs may be common in exoplanet observations. With over 100
Earth-sized exoplanets observed to date, it is important to be able to
identify the characteristics of Venus analogs. Thick layers of clouds,
such as those which enshroud Venus, are the regions most likely to be
observed on a Venus-like exoplanet. The cloud layers on Venus display a
wide range of wave-related features including global scale and smaller
scale gravity waves, Rossby and Kelvin waves, streak-like structures,
irregular dark regions, and vortices, and show considerable variations
with altitude. It is important to characterize these temporal and
spatial variations to understand the dynamics of the cloud-level
atmosphere on Venus or Venus-like exoplanets. Observed thermal phase
curves of exoplanets may show longitudinal variations, which could
indicate inhomogeneities in cloud cover, day-night differences,
variations in composition, or the influence of atmospheric waves, which
may shift the phase curve relative to the substellar point. To
understand and interpret observations of Venus or Venus-like exoplanets
at cloud altitudes, simulations have been performed using a Venus middle
atmosphere general circulation model. In this investigation we simulate
Rossby and Kelvin waves and modify forcing parameters, including the
resolution and dissipation, and compare the results with observations
from Venus probes, Venus Express and the Akatsuki mission.