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We present observations of Uranus in northern spring with the Very Large Array from 0.7 to 5 cm. These observations reveal details in thermal emission from Uranus' north pole at 10s of bars, including a dark collar near 80°N 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 10× depletion of NH3 or H2S vapor between 10 and 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.
Akins, A., Hofstadter, M., Butler, B., Friedson, A. J., Molter, E., Parisi, M., & de Pater, I. (2023, May 28). Evidence of a Polar Cyclone on Uranus From VLA Observations. Geophysical Research Letters. John Wiley and Sons Inc. https://doi.org/10.1029/2023GL102872