Uranus in 2003: Zonal winds, banded structure, and discrete features

Imaging of Uranus in 2003 with the Keck 10-m telescope reveals banded zonal structure and dozens of discrete cloud features at J and H bands; several features in the northern hemisphere are also detectable at K′. By tracking features over four days, we extend the zonal wind profile well into the northern hemisphere. We report the first measurements of wind velocities at latitudes − 13 ° , + 19 ° , and northward of + 43 ° , the first direct wind measurements near the equator, and the highest wind velocity seen yet on Uranus ( + 218  m / s ). At northern mid-latitudes ( + 20 ° to + 40 ° ), the winds appear to have accelerated when compared to earlier HST and Keck observations; southern wind speeds ( − 20 ° to − 43 ° ) have not changed since Voyager measurements in 1986. The equator of Uranus exhibits a subtle wave structure, indicated by diffuse patches roughly every 30° in longitude. The largest discrete cloud features on Uranus show complex structure extending over tens of degrees, reminiscent of activity seen around Neptuneʹs Great Dark Spot during the Voyager encounter with that planet. There is no sign of a northern “polar collar” as is seen in the south, but a number of discrete features seen at the “expected” latitudes may signal the early stages of development of a northern collar.