We present observations of Uranus in northern spring with the VLA from 0.7 cm to 5 cm. These observations reveal details in thermal emission from Uranus' north pole at 10s of bars, including a dark collar near 80N and a bright spot at the polar center. The bright central spot resembles observations of polar emission on Saturn and Neptune at shallower pressures. We constrain the variations in temperature and NH3/H2S abundances which could explain these features. We find that the brightness temperature of the polar spot can be recreated through 5 K temperature gradients and/or 10x depletion of NH3 or H2S vapor between 10-20 bars, both consistent with the presence of a cyclonic polar vortex. The contrast of the polar spot may have increased since 2015, which would suggest seasonal evolution of Uranus' polar circulation at depth.
@article{arxiv.2305.15521,
title = {Evidence of a Polar Cyclone on Uranus from VLA Observations},
author = {Alex Akins and Mark Hofstadter and Bryan Butler and A. James Friedson and Edward Molter and Marzia Parisi and Imke de Pater},
journal= {arXiv preprint arXiv:2305.15521},
year = {2023}
}
Comments
14 pages, 4 figures, accepted to Geophysical Research Letters