Reanalysis of Uranus' cloud scattering properties from IRTF/SpeX observations using a self-consistent scattering cloud retrieval scheme

摘要

We have developed a new retrieval approach to modelling near-infrared spectra of Uranus that represents a significant improvement over previous modelling methods. We reanalysed IRTF/SpeX observations of Uranus observed in 2009 covering the wavelength range 0.8-1.8 pm and reported by Tice et al. (Tice, D.S., Irwin, P.G.J., Fletcher, L.N., Teanby, N.A., Hurley, J., Orton, G.S., Davis, G.R. [2013]. Icarus 223,684-698). By retrieving the imaginary refractive index spectra of cloud particles we are able to consistently define the real part of the refractive index spectra, through a Kramers-Kronig analysis, and thus determine self-consistent extinction cross-section, single-scattering and phase-function spectra for the clouds and hazes in Uranus' atmosphere. We tested two different cloud-modelling schemes used in conjunction with the temperature/methane profile of Baines et al. (Baines, K.H., Mickelson, M.E., Larson, LE., Ferguson, D.W. [1995]. Icarus 114,328-340), a reanalysis of the Voyager-2 radio-occultation observations performed by Sromovsky, Fry and Kim (Sromovsky, L.A., Fry, P.M., Kim, J.H. [2011]. Icarus 215,292-312), and a recent determination from Spitzer (Orton, G.S., Fletcher, LN., Moses, J.I., Mainzer, A.K., Hines, D., Hammel, H.B., Martin-Torres, RI, Burgdorf, M., Merlet, C., Line, M.R. [2014]. Icarus 243, 494-513).