Evidence of a Polar Cyclone on Uranus From VLA Observations

We present observations of Uranus in northern spring with the Very Large Array from 0.7 to 5 cm. These observations reveal details in thermal emission from Uranus' north pole at 10s of bars, including a dark collar near 80°N and a bright spot at the polar center. The bright central spot resembles observations of polar emission on Saturn and Neptune at shallower pressures. We constrain the variations in temperature and NH3/H2S abundances which could explain these features. We find that the brightness temperature of the polar spot can be recreated through 5 K temperature gradients and/or 10× depletion of NH3 or H2S vapor between 10 and 20 bars, both consistent with the presence of a cyclonic polar vortex. The contrast of the polar spot may have increased since 2015, which would suggest seasonal evolution of Uranus' polar circulation at depth.

[1]  G. Orton,et al.  Subseasonal Variation in Neptune’s Mid-infrared Emission , 2021, The Planetary Science Journal.

[2]  R. K. Scott,et al.  Polar Vortices in Planetary Atmospheres , 2021, Reviews of Geophysics.

[3]  D. DeBoer,et al.  Neptune's Spatial Brightness Temperature Variations from the VLA and ALMA , 2021, 2104.06554.

[4]  B. Butler,et al.  Tropospheric Composition and Circulation of Uranus with ALMA and the VLA , 2020, 2010.11154.

[5]  G. Orton,et al.  Uranus in Northern Midspring: Persistent Atmospheric Temperatures and Circulations Inferred from Thermal Imaging , 2019, The Astronomical Journal.

[6]  G. Orton,et al.  Ice Giant Circulation Patterns: Implications for Atmospheric Probes , 2019, Space Science Reviews.

[7]  S. Brueshaber,et al.  Dynamical regimes of giant planet polar vortices , 2019, Icarus.

[8]  G. Orton,et al.  A hexagon in Saturn’s northern stratosphere surrounding the emerging summertime polar vortex , 2018, Nature Communications.

[9]  H. Hammel,et al.  The methane distribution and polar brightening on Uranus based on HST/STIS, Keck/NIRC2, and IRTF/SpeX observations through 2015 , 2018, Icarus.

[10]  C. Brogan,et al.  Advanced Gain Calibration Techniques in Radio Interferometry , 2018, 1805.05266.

[11]  R. Perley,et al.  An Accurate Flux Density Scale from 50 MHz to 50 GHz , 2016, 1609.05940.

[12]  H. Hammel,et al.  High S/N Keck and Gemini AO imaging of Uranus during 2012-2014: New cloud patterns, increasing activity, and improved wind measurements , 2015, 1512.05009.

[13]  E. Karkoschka,et al.  Uranus’ southern circulation revealed by Voyager 2: Unique characteristics , 2015 .

[14]  G. Orton,et al.  Neptune’s global circulation deduced from multi-wavelength observations , 2014 .

[15]  G. Orton,et al.  Neptune at summer solstice: Zonal mean temperatures from ground-based observations, 2003–2007 , 2013, 1311.7570.

[16]  H. Hammel,et al.  Post-equinox dynamics and polar cloud structure on Uranus ☆ , 2012, 1503.00592.

[17]  H. Hammel,et al.  Seeing double at Neptune's south pole , 2010, 1003.3240.

[18]  L. Debnath.  Geophysical Fluid Dynamics , 2008 .

[19]  Tim J. Cornwell,et al.  Multiscale CLEAN Deconvolution of Radio Synthesis Images , 2008, IEEE Journal of Selected Topics in Signal Processing.

[20]  K. Golap,et al.  CASA Architecture and Applications , 2007 .

[21]  L. Sromovsky,et al.  Dynamics of cloud features on Uranus , 2005, 1503.03714.

[22]  G. Orton,et al.  Saturn's Temperature Field from High-Resolution Middle-Infrared Imaging , 2005, Science.

[23]  I. Pater,et al.  Longitude-resolved imaging of Jupiter at λ=2 cm , 2004, astro-ph/0612769.

[24]  B. Butler,et al.  Seasonal change in the deep atmosphere of Uranus , 2002 .

[25]  E. Karkoschka.  Clouds of high contrast on Uranus. , 1998, Science.

[26]  R. Sault,et al.  Multi-frequency synthesis techniques in radio interferometric imaging. , 1994 .

[27]  I. Pater,et al.  Possible microwave absorption by H2S gas in Uranus' and Neptune's atmospheres , 1991 .

[28]  D. Muhleman,et al.  Vertical motions in the Uranian atmosphere: an analysis of radio observations , 1990 .

[29]  I. Pater,et al.  Uranus deep atmosphere revealed , 1989 .

[30]  D. Muhleman,et al.  Very Large Array observations of Uranus at 2.0 cm , 1988 .

[31]  P. Gierasch,et al.  Voyager infrared observations of Uranus' atmosphere: Thermal structure and dynamics , 1987 .

[32]  Steven T. Massie,et al.  Models of the millimeter-centimeter spectra of the giant planets , 1985 .

[33]  B. Butler.  Solar System Objects , 2002 .

[34]  C. Carilli,et al.  Synthesis Imaging in Radio Astronomy II , 1999 .