64 research outputs found
Effects of dissociation/recombination on the day-night temperature contrasts of ultra-hot Jupiters
Secondary eclipse observations of ultra-hot Jupiters have found evidence that
hydrogen is dissociated on their daysides. Additionally, full-phase light curve
observations of ultra-hot Jupiters show a smaller day-night emitted flux
contrast than that expected from previous theory. Recently, it was proposed by
Bell & Cowan (2018) that the heat intake to dissociate hydrogen and heat
release due to recombination of dissociated hydrogen can affect the atmospheric
circulation of ultra-hot Jupiters. In this work, we add cooling/heating due to
dissociation/recombination into the analytic theory of Komacek & Showman (2016)
and Zhang & Showman (2017) for the dayside-nightside temperature contrasts of
hot Jupiters. We find that at high values of incident stellar flux, the
day-night temperature contrast of ultra-hot Jupiters may decrease with
increasing incident stellar flux due to dissociation/recombination, the
opposite of that expected without including the effects of
dissociation/recombination. We propose that a combination of a greater number
of full-phase light curve observations of ultra-hot Jupiters and future General
Circulation Models that include the effects of dissociation/recombination could
determine in detail how the atmospheric circulation of ultra-hot Jupiters
differs from that of cooler planets.Comment: Accepted at Research Notes of the AA
Structure and Evolution of Internally Heated Hot Jupiters
Hot Jupiters receive strong stellar irradiation, producing equilibrium
temperatures of . Incoming irradiation directly
heats just their thin outer layer, down to pressures of $\sim 0.1 \
\mathrm{bars}1 - 10 \ \mathrm{bars}\gtrsim 10\%100 \ \mathrm{bars}1\%1.4 R_{\rm Jup}10^4 \ \mathrm{bars}\approx 99\%$ of the planet's mass -- suppresses planetary cooling
as effectively as heating at the center. In summary, we find that relatively
shallow heating is required to explain the radii of most hot Jupiters, provided
that this heat is applied early and persists throughout their evolution.Comment: Accepted at ApJ, 14 pages, 10 figure
Atmospheric Circulation of Hot Jupiters: Dayside-Nightside Temperature Differences. II. Comparison with Observations
The full-phase infrared light curves of low-eccentricity hot Jupiters show a
trend of increasing fractional dayside-nightside brightness temperature
difference with increasing incident stellar flux, both averaged across the
infrared and in each individual wavelength band. The analytic theory of Komacek
& Showman (2016) shows that this trend is due to the decreasing ability with
increasing incident stellar flux of waves to propagate from day to night and
erase temperature differences. Here, we compare the predictions of this theory
to observations, showing that it explains well the shape of the trend of
increasing dayside-nightside temperature difference with increasing equilibrium
temperature. Applied to individual planets, the theory matches well with
observations at high equilibrium temperatures but, for a fixed photosphere
pressure of , systematically under-predicts the
dayside-nightside brightness temperature differences at equilibrium
temperatures less than . We interpret this as due to as the
effects of a process that moves the infrared photospheres of these cooler hot
Jupiters to lower pressures. We also utilize general circulation modeling with
double-grey radiative transfer to explore how the circulation changes with
equilibrium temperature and drag strengths. As expected from our theory, the
dayside-nightside temperature differences from our numerical simulations
increase with increasing incident stellar flux and drag strengths. We calculate
model phase curves using our general circulation models, from which we compare
the broadband infrared offset from the substellar point and dayside-nightside
brightness temperature differences against observations, finding that strong
drag or additional effects (e.g. clouds and/or supersolar metallicities) are
necessary to explain many observed phase curves.Comment: Accepted at ApJ, 16 pages, 11 figure
Vertical Tracer Mixing in Hot Jupiter Atmospheres
Aerosols appear to be ubiquitous in close-in gas giant atmospheres, and
disequilibrium chemistry likely impacts the emergent spectra of these planets.
Lofted aerosols and disequilibrium chemistry are caused by vigorous vertical
transport in these heavily irradiated atmospheres. Here we numerically and
analytically investigate how vertical transport should change over the
parameter space of spin-synchronized gas giants. In order to understand how
tracer transport depends on planetary parameters, we develop an analytic theory
to predict vertical velocities and mixing rates () and compare
the results to our numerical experiments. We find that both our theory and
numerical simulations predict that, if the vertical mixing rate is described by
an eddy diffusivity, then this eddy diffusivity should increase
with increasing equilibrium temperature, decreasing frictional drag strength,
and increasing chemical loss timescales. We find that the transition in our
numerical simulations between circulation dominated by a superrotating jet and
that with solely day-to-night flow causes a marked change in the vertical
velocity structure and tracer distribution. The mixing ratio of passive tracers
is greatest for intermediate drag strengths that corresponds to this transition
between a superrotating jet with columnar vertical velocity structure and
day-to-night flow with upwelling on the dayside and downwelling on the
nightside. Lastly, we present analytic solutions for as a
function of planetary effective temperature, chemical loss timescales, and
other parameters, for use as input to one-dimensional chemistry models of
spin-synchronized gas giant atmospheres.Comment: 25 pages, 12 figures, Accepted at Ap
Greater Climate Sensitivity and Variability on TRAPPIST-1e than Earth
The atmospheres of rocky exoplanets are close to being characterized by
astronomical observations, in part due to the commissioning of the James Webb
Space Telescope. These observations compel us to understand exoplanetary
atmospheres, in the voyage to find habitable planets. With this aim, we
investigate the effect that CO partial pressure (pCO) has on
exoplanets' climate variability, by analyzing results from ExoCAM model
simulations of the tidally locked TRAPPIST-1e exoplanet, an Earth-like
aqua-planet and Earth itself. First, we relate the differences between the
planets to their elementary parameters. Then, we compare the sensitivity of the
Earth analogue and TRAPPIST-1e's surface temperature and precipitation to
pCO. Our simulations suggest that the climatology and extremes of
TRAPPIST-1e's temperature are 1.5 times more sensitive to pCO
relative to Earth. The precipitation sensitivity strongly depends on the
specific region analyzed. Indeed, the precipitation near mid-latitude and
equatorial sub-stellar regions of TRAPPIST-1e is more sensitive to pCO, and
the precipitation sensitivity is 2 times larger in TRAPPIST-1e. A
dynamical systems perspective, which provides information about how the
atmosphere evolves in phase-space, provides additional insights. Notably, an
increase in pCO, results in an increase in atmospheric persistence on both
planets, and the persistence of TRAPPIST-1e is more sensitive to pCO than
Earth. We conclude that the climate of TRAPPIST-1e may be more sensitive to
pCO, particularly on its dayside. This study documents a new pathway for
understanding the effect that varying planetary parameters have on the climate
variability of potentially habitable exoplanets and on Earth.Comment: Accepted at Ap
Greater climate sensitivity and variability on TRAPPIST-1e than Earth
The atmospheres of rocky exoplanets are close to being characterized by
astronomical observations, in part due to the commissioning of the James Webb
Space Telescope. These observations compel us to understand exoplanetary
atmospheres, in the voyage to find habitable planets. With this aim, we
investigate the effect that CO partial pressure (pCO) has on
exoplanets' climate variability, by analyzing results from ExoCAM model
simulations of the tidally locked TRAPPIST-1e exoplanet, an Earth-like
aqua-planet and Earth itself. First, we relate the differences between the
planets to their elementary parameters. Then, we compare the sensitivity of the
Earth analogue and TRAPPIST-1e's surface temperature and precipitation to
pCO. Our simulations suggest that the climatology and extremes of
TRAPPIST-1e's temperature are 1.5 times more sensitive to pCO
relative to Earth. The precipitation sensitivity strongly depends on the
specific region analyzed. Indeed, the precipitation near mid-latitude and
equatorial sub-stellar regions of TRAPPIST-1e is more sensitive to pCO, and
the precipitation sensitivity is 2 times larger in TRAPPIST-1e. A
dynamical systems perspective, which provides information about how the
atmosphere evolves in phase-space, provides additional insights. Notably, an
increase in pCO, results in an increase in atmospheric persistence on both
planets, and the persistence of TRAPPIST-1e is more sensitive to pCO than
Earth. We conclude that the climate of TRAPPIST-1e may be more sensitive to
pCO, particularly on its dayside. This study documents a new pathway for
understanding the effect that varying planetary parameters have on the climate
variability of potentially habitable exoplanets and on Earth.Comment: Accepted at Ap
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