Vertical Tracer Mixing in Hot Jupiter Atmospheres [EPA]

http://arxiv.org/abs/1904.09676


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.

Read this paper on arXiv…

T. Komacek, A. Showman and V. Parmentier
Tue, 23 Apr 19
20/58

Comments: 23 pages, 11 figures, submitted to AAS Journals