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Uranus in Northern Mid-Spring: Persistent Atmospheric Temperatures and Circulations Inferred from Thermal Imaging

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posted on 28.04.2020, 10:30 by Michael T Roman, Leigh N Fletcher, Glenn S Orton, Naomi Rowe-Gurney, Patrick GJ Irwin
We present results from mid-infrared imaging of Uranus at wavelengths of 13.0 micron and 18.7 micron, sensing emission from the stratosphere and upper troposphere, acquired using the VISIR instrument at the Very Large Telescope (VLT), September 4-October 20, 2018. Using a combination of inverse and forward modeling, we analyze these northern mid-spring (L_s~46) images and compare them to archival data to assess seasonal changes since the 1986 southern solstice and subsequent equinox. We find the data are consistent with little change (< 0.3 K) in the upper tropospheric temperature structure, extending the previous conclusions of Orton et al (2015) well past equinox, with only a subtle increase in temperature at the emerging north pole. Additionally, spatial-temporal variations in 13 micron stratospheric emission are investigated for the first time, revealing meridional variation and a hemispheric asymmetry not predicted by models. Finally, we investigate the nature of the stratospheric emission and demonstrate that the observed distribution appears related and potentially coupled to the underlying tropospheric emission six scale heights below. The observations are consistent with either mid-latitude heating or an enhanced abundance of acetylene. Considering potential mechanisms and additional observations, we favor a model of acetylene enrichment at mid-latitudes resulting from an extension of the upper-tropospheric circulation, which appears capable of transporting methane from the troposphere, through the cold trap, and into the stratosphere for subsequent photolysis to acetylene.


This analysis was based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere under ESO programmes 0101.C-0073(B) and 083.C-0162(A). This work was supported by a European Research Council Consolidator grant, under the European Unions Horizons 2020 research and innovation programme, grant No. 723890. L.N.F. was also supported by a Royal Society Research fellowship. G.S.O. was supported by NASA through funds distributed to the Jet Propulsion Laboratory, California Institute of Technology. This work used the ALICE supercomputing facilities provided by the university of Leicester. This work used data acquired from the NASA/ESA HST Space Telescope, associated with OPAL program (PI: Simon, GO13937), and archived by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. All maps are available at



The Astronomical Journal, 159:45 (16pp), 2020 February

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