  Observations of Uranus were made on the 8/9th November with HST/WFC3 at a
time when a huge cloud complex was present at 30 - 40N. We imaged Uranus in
seven filters spanning 467 - 924 nm, and analysed these observations with the
NEMESIS radiative-transfer and retrieval code.
  The same system was also observed in the H-band with VLT/SINFONI ON 31st
October and 11th November (Irwin et al., 2016). To constrain the background
cloud particle sizes and scattering properties we conducted a limb-darkening
analysis of the background cloud structure at 30-40N by simultaneously fitting:
a) these HST/OPAL observations at a range of zenith angles; b) the VLT/SINFONI
observations at a range of zenith angles; and c) IRTF/SpeX observations made in
2009 (Irwin et al., 2015).
  We find that the observations are well modelled with a three-component cloud
comprised of: 1) a vertically thin, but optically thick 'deep' tropospheric
cloud at a pressure of ~2 bars; 2) a methane-ice cloud at the
methane-condensation level with variable vertical extent; and 3) a vertically
extended tropospheric haze. We find that the particles sizes in both haze and
tropospheric cloud have an effective radius of ~0.1 micron, although we cannot
rule out larger particle sizes in the tropospheric cloud.
  We find that the particles in both the tropospheric cloud and haze are more
scattering at short wavelengths, giving them a blue colour, but are more
absorbing at longer wavelengths, especially for the tropospheric haze. For the
particles in the storm clouds, which we assume to be composed of methane ice
particles, we find that their mean radii must be ~0.5 micron. We find that the
high clouds have low integrated opacity, and that "streamers" reminiscent of
thunderstorm anvils are confined to levels deeper than 1 bar. These results
argue against vigorous moist convective origins for the cloud features.
