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Constraints on Uranus's haze structure, formation and transport

Authors :
Glenn S. Orton
Pascal Rannou
Michael H. Wong
Patrick G. J. Irwin
Daniel Toledo
Nicholas A Teanby
Amy Simon
Department of Atmospheric, Oceanic and Planetary Physics [Oxford] (AOPP)
University of Oxford [Oxford]
Groupe de spectrométrie moléculaire et atmosphérique (GSMA)
Université de Reims Champagne-Ardenne (URCA)-Centre National de la Recherche Scientifique (CNRS)
School of Earth Sciences [Bristol]
University of Bristol [Bristol]
NASA Goddard Space Flight Center (GSFC)
Department of Astronomy [Berkeley]
University of California [Berkeley]
University of California-University of California
Jet Propulsion Laboratory (JPL)
California Institute of Technology (CALTECH)-NASA
Source :
Icarus, Icarus, Elsevier, 2019, 333 (6), pp.1-11. ⟨10.1016/j.icarus.2019.05.018⟩, Toledo, D, Irwin, P G J, Rannou, P, Teanby, N A, Simon, A A, Wong, M H & Orton, G S 2019, ' Constraints on Uranus's haze structure, formation and transport ', Icarus, vol. 333, pp. 1-11 . https://doi.org/10.1016/j.icarus.2019.05.018
Publication Year :
2019
Publisher :
HAL CCSD, 2019.

Abstract

Microphysical simulations have been performed to constrain the formation and structure of haze in Uranus's atmosphere. These simulations were coupled to a radiative-transfer code to fit observations performed by the SINFONI Integral Field Unit Spectrometer on the Very Large Telescope (VLT)and by the Wide Field Camera 3 (WFC3)of the Hubble Space Telescope (HST)in 2014. Our simulations yield an effective radius of ∼0.2 μm for the haze particles in the tropopause and a density of ∼2.9 particles per cm 3. Our simulations also provide an estimate for the haze production rate in the stratosphere of between ∼3.10 −16 and 3.10 −15 kg m −2 s −1, about 100 times smaller than that found in Titan's atmosphere (e.g. Rannou et al., 2004). This range of values is very similar to that derived by Pollack et al. (1987)from Voyager-2 observations in 1986, suggesting microphysical timescales greater than the elapsed time between these observations (28 years, or 1/3 of a Uranian year). This result is in agreement with analyses performed with our microphysical model that show timescales for haze particles to grow and settle out to be >∼30 years at pressure levels >0.1 bar. However, these timescales are too big to explain the observed variations in the haze structure over Uranus's northern hemisphere after 2007 equinox (e.g. de Pater et al., 2015). This indicates that dynamics may be the main factor controlling the spatial and temporal distribution of the haze over the poles. A meridional stratospheric transport of haze particles with winds velocities >∼0.025 m s −1 would result in dynamics timescales shorter than 30 years and thus may explain the observed variations in the haze structure.

Details

Language :
English
ISSN :
00191035 and 10902643
Database :
OpenAIRE
Journal :
Icarus, Icarus, Elsevier, 2019, 333 (6), pp.1-11. ⟨10.1016/j.icarus.2019.05.018⟩, Toledo, D, Irwin, P G J, Rannou, P, Teanby, N A, Simon, A A, Wong, M H & Orton, G S 2019, ' Constraints on Uranus's haze structure, formation and transport ', Icarus, vol. 333, pp. 1-11 . https://doi.org/10.1016/j.icarus.2019.05.018
Accession number :
edsair.doi.dedup.....c3014fe9e7fd6677bada9a64f3c871f8
Full Text :
https://doi.org/10.1016/j.icarus.2019.05.018⟩