What is the nature of bright spots found on Uranus? actually quotes Space.com's Uranus Has a Dark Spot which says:
During the past decade, many bright spots have been seen on Uranus in both red and near-infrared filters. But this is the first dark spot ever seen on the planet.
Question: So I'd like to know if there is any science-based thinking on the underlying nature of the dark spot on Uranus beyond "it looks dark, like the ones on Neptune". Has this all been sorted out or is it still mostly a mystery?
Wikipedia's Climate of Uranus; Uranus Dark Spot gives a lot of descriptive information and relates the spot to similar things seen on Neptune, and describes some speculation, but this article does not seem explain much.
Just as we near the end of the hurricane season in the Atlantic Ocean, winds whirl and clouds churn 2 billion miles away in the atmosphere of Uranus, forming a dark vortex large enough to engulf two-thirds of the United States. (Image credit: NASA, ESA, L. Sromovsky and P. Fry / University of Wisconsin)