Vertical Tracer Mixing in Hot Jupiter Atmospheres. (arXiv:1904.09676v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Komacek_T/0/1/0/all/0/1">Thaddeus D. Komacek</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Showman_A/0/1/0/all/0/1">Adam P. Showman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Parmentier_V/0/1/0/all/0/1">Vivien Parmentier</a>
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
mixing in these heavily irradiated atmospheres. Here we numerically and
analytically investigate how vertical mixing should change over the parameter
space of spin-synchronized gas giants. We develop an analytic theory to predict
vertical velocities and mixing rates ($K_{zz}$). We find that both our theory
and numerical simulations predict that, if the vertical mixing is described by
an eddy diffusivity, then this eddy diffusivity $K_{zz}$ should increase with
increasing equilibrium temperature, decreasing frictional drag strength, and
increasing chemical loss timescales. We conduct numerical simulations to
investigate how vertical mixing depends on planetary parameters with two types
of passive tracers, one representing chemical relaxation and one representing
particles that settle. 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 $K_{zz}$ 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.
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
mixing in these heavily irradiated atmospheres. Here we numerically and
analytically investigate how vertical mixing should change over the parameter
space of spin-synchronized gas giants. We develop an analytic theory to predict
vertical velocities and mixing rates ($K_{zz}$). We find that both our theory
and numerical simulations predict that, if the vertical mixing is described by
an eddy diffusivity, then this eddy diffusivity $K_{zz}$ should increase with
increasing equilibrium temperature, decreasing frictional drag strength, and
increasing chemical loss timescales. We conduct numerical simulations to
investigate how vertical mixing depends on planetary parameters with two types
of passive tracers, one representing chemical relaxation and one representing
particles that settle. 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 $K_{zz}$ 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.
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