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The temporal brightening of Uranus’ northern polar hood from HST/WFC3 & HST/STIS observations
  • +8
  • Arjuna James,
  • Patrick G.J. Irwin,
  • Jack Dobinson,
  • Michael H. Wong,
  • Troy K. Tsubota,
  • Amy Simon,
  • Leigh N Fletcher,
  • Michael Thomas Roman,
  • Nicholas Teanby,
  • Daniel Toledo,
  • Glenn S Orton
Arjuna James
University of Oxford

Corresponding Author:[email protected]

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Patrick G.J. Irwin
University of Oxford
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Jack Dobinson
University of Oxford
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Michael H. Wong
University of California, Berkeley
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Troy K. Tsubota
University of California, Berkeley
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Amy Simon
NASA GSFC
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Leigh N Fletcher
University of Leicester
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Michael Thomas Roman
University of Leicester
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Nicholas Teanby
University of Bristol
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Daniel Toledo
Instituto Nacional de Técnica Aeroespacial (INTA), Madrid, Spain.
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Glenn S Orton
Jet Propulsion Laboratory, California Institute of Technology
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Abstract

Hubble Space Telescope Wide-Field Camera 3 (HST/WFC3) observations spanning 2015 to 2021 confirm a brightening of Uranus’ north polar hood feature with time. The vertical aerosol model of Irwin et al. (2023) (IRW23), consisting of a deep haze layer based at ~5 bar, a 1 - 2 bar haze layer, and an extended haze rising up from the 1 - 2 bar layer, was applied to retrievals on HST Space Telescope Imaging Spectrograph (HST/STIS) observations (Sromovsky et al., 2014, 2019} revealing a reduction in cloud-top CH4 by an average of 0.19 {plus minus} 0.03% between 40 - 80{degree sign}N between 2012 and 2015. A combination of latitudinal retrievals on the HST/WFC3 & HST/STIS datasets, again employing the IRW23 model, reveal a temporal thickening of the 1 - 2 bar haze layer to be the main cause of the polar hood brightening, finding an average increase of 1.09 {plus minus} 0.08 at 0.8 μm north of ~45{degree sign}N, concurrent with a decrease in the imaginary refractive index spectrum of the 1 - 2 bar haze layer north of ~40{degree sign}N and longwards of ~0.7 μm, and between 60{degree sign}N and 80{degree sign}N at ~0.5 μm. Small contributions to the brightening were found from a thickening of the deep aerosol layer, with an average increase in integrated opacity of 0.6 {plus minus} 0.1 north of 45{degree sign}N between 2012 and 2015, and from the aforementioned decrease in cloud-top CH4 abundance. Our results are consistent with the slowing of a meridional circulation, exhibiting strong subsidence at the poles.
16 May 2023Submitted to ESS Open Archive
25 May 2023Published in ESS Open Archive