Planetary Climate Dynamics

Abstract:

The data comprise two 2-dimensional gridded maps of horizontal wind measurements covering the north and south polar regions of Saturn, as previously published by Antuñano et al. (2015). As fully described in that paper, these measurements were derived from sets of Cassini Orbiter Imaging Sub-System (ISS) Wide Angle Camera (WAC) and Narrow Angle Camera (NAC) images using the continuum band CB2 and CB3 filters, acquired for the northern hemisphere in June 2013 and for the southern hemisphere using WAC CB2 and CB3 images taken in October 2006 and December 2008. Additional NAC images using the CB2 and red filters taken in July 2008 were also used to analyse the southern polar vortex. The WAC images covered a region extending from a planetocentric latitude of around 60-65 degrees to each pole (apart from a segment in longitude between around 35 - 110 degrees W) with a horizontal resolution equivalent to around 0.05 degrees latitude (around 50km) per pixel, while NAC images were mostly used for the polar vortices, with a resolution equivalent to around 0.01 degrees latitude (around 10 km) per pixel. Horizontal velocities were obtained using semi-automated image correlation methods between pairs of images separated in time by intervals of approximately 1-10 hours. The correlation algorithm used pixel box sizes of 23 x 23 (in the north) or 25 x 25 (in the south), leading to a spatial resolution of the velocity vectors equivalent to around 1 degree latitude or 1000 km outside the polar vortices, reducing to around 0.2 degrees or 200 km within the polar vortices themselves. The automatically generated velocity vectors were supplemented by a small number (around 1% of the total) of vectors obtained manually from the motion of visually identified cloud tracers. The estimated measurement uncertainty on each vector was around 5-10 m/s. The original velocity vectors from Antuñano et al. (2015) were interpolated onto a regular latitude-longitude grid using convex hulls and Delauney triangulation via the QHULL routine of the Interactive Data Language (IDL). The final datasets are held on a regular grid separated by 3-4 degrees in longitude and 0.23 degrees in latitude. Data are stored as two text files, tabulating the latitude and (west) longitude of each point and the eastward and northward velocity components respectively in units of m/s. Reference: Antuñano,A., del Río-Gaztelurrutia,T., Sánchez-Lavega,A., & Hueso, R. (2015). Dynamics of Saturn’s polar regions. J. Geophys. Res.: Planets, 120, 155–176. doi: 10.1002/2014JE004709

Abstract:

This archive contains the Python code used to analyse and plot the data in Hammond & Lewis 2021, "The rotational and divergent components of atmospheric circulation on tidally locked planets", as well as the data from the "terrestrial" simulation of the atmosphere of a rocky planet using the general circulation model ExoFMS. It contains three files: 1) HL21_plotter.ipynb This is a Jupyter notebook containing Python code. It reads the data from the ExoFMS simulation and finds its rotational and divergent parts. It then plots the figures used in Hammond & Lewis 2021. 2) data/rotdiv-terr-control-1000-2000_atmos_average_interp.nc The "terrestrial" simulation output, interpolated to uniform pressure levels. This is used to plot quantities such as velocity at a constant pressure. 3) data/rotdiv-terr-control-1000-2000_atmos_average.nc The "terrestrial" simulation output, on the raw model sigma-pressure levels. This is used to calculate the dry static energy budget. The paper also uses a "Hot Jupiter" simulation from the THOR GCM. This is from "THOR 2.0: Major Improvements to the Open-Source General Circulation Model" (Deitrick et al. 2020). The data is available on request to Russell Deitrick (russell.deitrick@csh.unibe.ch). The same analysis can be made using HL21_plotter.ipynb, with small modifications due to the different grid in THOR.

Abstract:

Images of the giant planets Jupiter and Saturn show highly turbulent storms and swirling clouds that reflect the intensity of turbulence in their atmospheres. Quantifying planetary turbulence is inaccessible to conventional tools, however, since they require large quantities of spatially and temporally resolved data. Here we show, using experiments, observations, and simulations, that potential vorticity (PV) is a straightforward and universal diagnostic that can be used to estimate turbulent energy transfer in a stably stratified atmosphere. We use the conservation of PV to define a length scale, LM, representing a typical distance over which PV is mixed by planetary turbulence. LM increases as the turbulent intensity increases and can be estimated from any latitudinal PV profile. Using this principle, we estimate LM within Jupiter's and Saturn's tropospheres, showing for the first time that turbulent energy transfer in Saturn's atmosphere is four times less intense than Jupiter's.

Abstract:

Groundbased and spacecraft telescopic observations, combined with an intensive modeling effort, have greatly enhanced our understanding of hot giant planets and brown dwarfs over the past ten years. Although these objects are all fluid, hydrogen worlds with stratified atmospheres overlying convective interiors, they exhibit an impressive diversity of atmospheric behavior. Hot Jupiters are strongly irradiated, and a wealth of observations constrain the day-night temperature differences, circulation, and cloudiness. The intense stellar irradiation, presumed tidal locking and modest rotation leads to a novel regime of strong day-night radiative forcing. Circulation models predict large day-night temperature differences, global-scale eddies, patchy clouds, and, in most cases, a fast eastward jet at the equator—equatorial superrotation. The warm Jupiters lie farther from their stars and are not generally tidally locked, so they may exhibit a wide range of rotation rates, obliquities, and orbital eccentricities, which, along with the weaker irradiation, leads to circulation patterns and observable signatures predicted to differ substantially from hot Jupiters. Brown dwarfs are typically isolated, rapidly rotating worlds; they radiate enormous energy fluxes into space and convect vigorously in their interiors. Their atmospheres exhibit patchiness in clouds and temperature on regional to global scales—the result of modulation by large-scale atmospheric circulation. Despite the lack of irradiation, such circulations can be driven by interaction of the interior convection with the overlying atmosphere, as well as self-organization of patchiness due to cloud-dynamical-radiative feedbacks. Finally, irradiated brown dwarfs help to bridge the gap between these classes of objects, experiencing intense external irradiation as well as vigorous interior convection. Collectively, these diverse objects span over six orders of magnitude in intrinsic heat flux and incident stellar flux, and two orders of magnitude in rotation rate—thereby placing strong constraints on how the circulation of giant planets (broadly defined) depend on these parameters. A hierarchy of modeling approaches have yielded major new insights into the dynamics governing these phenomena.