(a) Abundance and temperature profiles of the main constituents of Uranus upper atmosphere, as inferred from the occultation observations by the Voyager 2 ultraviolet spectrometer. Helium was not detectable in the occultations hence it has been extrapolated upwards from IRIS measurements (Hanel et al. 1986). From Herbert et al. (1987). (b) Modelled ionospheric profiles of electron densities for Uranus using the Voyager inferred temperature profiles. From Waite & Cravens (1987).