Exploration of the circulation and cloud structure of the atmospheres of the Giant Planets with ground- and space-based telescopes

Voyager 2 flew past Uranus and Neptune in 1986 and 1989, and provided our only close-up views of these ice giant worlds. Now, more than a quarter of a century later, the ice giants are recognised as key destinations for future planetary missions and as our closest examples of a planetary class that appears commonplace throughout our galaxy. The Voyager flybys revealed dynamic worlds with atmospheres quite unlike the familiar banded cloud structures seen on Jupiter and Saturn, but the brevity of these encounters prevented detailed scrutiny. Uranus was shown to be rather sluggish, whereas Neptune featured dynamic cloud activity and vortices. This difference has never been satisfactorily explained and subsequent ground-based observations have since suggested that the activity on both of these planets varies hugely with time.

This project aims to construct a three-dimensional understanding of ice giant atmospheres to connect activity in the tropospheric weather layer (where convective clouds form and are sheared apart) to the middle atmosphere (the stratosphere, dominated by wave activity and photochemistry). The candidate would attempt to link changes in cloud activity and albedo in reflectivity spectra (wavelengths < 3 um) measured by instruments such as VLT/MUSE and VLT/SINFONI, with the temperature and composition of the ice giants as measured in thermal-infrared spectra (wavelengths> 5 um, e.g., VLT/VISIR, Spitzer) to reveal the underlying dynamics and circulations of these ice giant atmospheres. This work will be used to determine the spatial variation, vertical distribution and temporal evolution of temperature and cloud activity and better understand the condensation processes at work in these frigid atmospheres. This work will be used to plan and execute further observations and also prepare for the reduction of planned observations made with NASA's James Webb Space Telescope (JWST), scheduled for launch in 2021.

The key result of this project will be a self-consistent picture of the circulation and cloud-forming processes at work on the ice giants, paving the way for future atmospheric studies by visiting spacecraft.