Equatorial jet in the lower to middle cloud layer of Venus revealed by Akatsuki

The Venusian atmosphere is in a state of superrotation where prevailing westward winds move much faster than the planet’s rotation. Venus is covered with thick clouds that extend from about 45 to 70 km altitude, but thermal radiation emitted from the lower atmosphere and the surface on the planet’s night-side escapes to space at narrow spectral windows of near-infrared. The radiation can be used to estimate winds by tracking the silhouettes of clouds in the lower and middle cloud regions below about 57 km in altitude. Estimates of wind speeds have ranged from 50 to 70 m/s at low- to mid-latitudes, either nearly constant across latitudes or with winds peaking at mid-latitudes. Here we report the detection of winds at low latitude exceeding 80 m/s using IR2 camera images from the Akatsuki orbiter taken during July and August 2016. The angular speed around the planetary rotation axis peaks near the equator, which we suggest is consistent with an equatorial jet, a feature that has not been observed previously in the Venusian atmosphere. The mechanism producing the jet remains unclear. Our observations reveal variability in the zonal flow in the lower and middle cloud region that may provide new challenges and clues to the dynamics of Venus’s atmospheric superrotation.

[1]  K. Hodapp,et al.  Ground-Based Near-Infrared Imaging Observations of Venus During the Galileo Encounter , 1991, Science.

[2]  M. Taguchi,et al.  Overview of Venus orbiter, Akatsuki , 2011 .

[3]  L. Bengtsson,et al.  Models of Venus atmosphere , 2013 .

[4]  Takeshi Imamura,et al.  Long‐term variation in the cloud‐tracked zonal velocities at the cloud top of Venus deduced from Venus Express VMC images , 2013 .

[5]  V. Kerzhanovich,et al.  Venera 8: Measurements of Temperature, Pressure and Wind Velocity on the Illuminated Side of Venus 1 , 1973 .

[6]  S. Limaye.  Venus atmospheric circulation: Known and unknown , 1990 .

[7]  Frédéric Hourdin,et al.  Superrotation of Venus' atmosphere analyzed with a full general circulation model , 2010 .

[8]  P. Gierasch.  Meridional Circulation and the Maintenance of the Venus Atmospheric Rotation , 1975 .

[9]  J. Apt,et al.  Structure and circulation of the Venus atmosphere , 1980 .

[10]  T. Encrenaz,et al.  Probing Venus's cloud structure with Galileo NIMS , 1993 .

[11]  Takeshi Imamura,et al.  Automated cloud tracking system for the Akatsuki Venus Climate Orbiter data , 2012 .

[12]  L. Bengtsson,et al.  Towards understanding the climate of Venus , 2013 .

[13]  K. Hodapp,et al.  The Nature of the Near-Infrared Features on the Venus Night Side , 1989, Science.

[14]  P. Read,et al.  Exploring the Venus global super-rotation using a comprehensive general circulation model , 2016, 1609.06549.

[15]  G. Schubert,et al.  Zonal winds in the middle atmosphere of Venus from Pioneer Venus radio occultation data , 1984 .

[16]  Javier Peralta,et al.  A reanalysis of Venus winds at two cloud levels from Galileo SSI images , 2007 .

[17]  V. M. Linkin,et al.  Structure of the Venus atmosphere , 2007 .

[18]  Masaru Yamamoto,et al.  Formation and Maintenance of the 4-Day Circulation in the Venus Middle Atmosphere. , 1997 .

[19]  T. Imamura,et al.  Microphysics of Venusian Clouds in Rising Tropical Air , 2001 .

[20]  J. Crawford,et al.  Cloud structure on the dark side of Venus , 1984, Nature.

[21]  T V Johnson,et al.  Galileo Infrared Imaging Spectroscopy Measurements at Venus , 1991, Science.

[22]  A. Sánchez-Lavega,et al.  Assessing the long-term variability of Venus winds at cloud level from VIRTIS–Venus Express , 2012 .

[23]  M. Takagi,et al.  Effects of thermal tides on the Venus atmospheric superrotation , 2007 .

[24]  Takeshi Horinouchi,et al.  Improved automatic estimation of winds at the cloud top of Venus using superposition of cross-correlation surfaces , 2016 .

[25]  M. Kimata,et al.  Development and in-flight calibration of IR2: 2-μm camera onboard Japan’s Venus orbiter, Akatsuki , 2016, Earth, Planets and Space.

[26]  M. Taguchi,et al.  Large stationary gravity wave in the atmosphere of Venus , 2017 .

[27]  Kevin McGouldrick,et al.  An investigation of possible causes of the holes in the condensational Venus cloud using a microphysical cloud model with a radiative-dynamical feedback , 2007 .

[28]  Hollis G. Potter,et al.  Author Manuscript , 2013 .

[29]  T. Toda,et al.  AKATSUKI returns to Venus , 2016, Earth, Planets and Space.

[30]  H. Kashimura,et al.  Regime Diagrams of Solutions in an Idealized Quasi-Axisymmetric Model for Superrotation of Planetary Atmospheres , 2015 .

[31]  Giuseppe Piccioni,et al.  Variable winds on Venus mapped in three dimensions , 2008 .

[32]  Y. Matsuda,et al.  Dynamics of the Four-Day Circulation in the Venus Atmosphere , 1980 .

[33]  Atsushi Yamazaki,et al.  Image velocimetry for clouds with relaxation labeling based on deformation consistency , 2017 .

[34]  G. Schubert,et al.  GENERAL CIRCULATION AND THE DYNAMICAL STATE OF THE VENUS ATMOSPHERE , 2022, Venus.

[35]  Robert W. Boese,et al.  Greenhouse models of Venus' High surface temperature, as constrained by Pioneer Venus measurements , 1980 .

[36]  Masaru Yamamoto,et al.  The Fully Developed Superrotation Simulated by a General Circulation Model of a Venus-like Atmosphere , 2003 .

[37]  J. Whitehead,et al.  Moving Flame Experiment with Liquid Mercury: Possible Implications for the Venus Atmosphere , 1969, Science.

[38]  S. Fels,et al.  The interaction of thermally excited gravity waves with mean flows , 1973 .

[39]  D. Hunten,et al.  The microphysics of the clouds of Venus: Results of the Pioneer Venus Particle Size Spectrometer Experiment , 1980 .

[40]  Gabriella Gilli,et al.  Wave analysis in the atmosphere of Venus below 100-km altitude, simulated by the LMD Venus GCM , 2016 .

[41]  V. V. Kerzhanovich,et al.  Circulation of the atmosphere from the surface to 100 km , 1985 .