P029-07
Structure and Variability of the Venusian Upper Atmosphere Revealed by a GCM

Wednesday, 9 December 2020: 07:38
Virtual
Thomas Navarro, University of California Los Angeles, Los Angeles, CA, United States, Gabriella Gilli, Observatorio Astronomico De Lisboa, Lisbon, Portugal, Gerald Schubert, UCLA, Los Angeles, CA, United States, Sebastien Lebonnois, CNRS, Paris Cedex 16, France and Franck Lefèvre, LATMOS Laboratoire Atmosphères, Observations Spatiales, Sorbonne université, UVSQ Université Paris-Saclay, CNRS, Paris, France
Recorded Presentation
Abstract:
Above 90 km of altitude, the Venusian atmosphere is dominated by a strong day-to-night thermal gradient, inducing a Subsolar to Antisolar (SS-AS) circulation, with air flowing from the dayside to the nightside. Measurements have shown a considerable spatio-temporal variability of the SS-AS winds, temperature, and airglows, not well reproduced by previous General Circulation Models (GCM). Moreover, the transition from the Retrograde Zonal Superrotation (RZS) of the cloud deck to the SS-AS circulation is not well understood.

In order to investigate the Venusian upper atmosphere, we use the full physics ground-to-thermosphere Institut Pierre-Simon Laplace (IPSL) Venus GCM, with a photochemical model of 34 advected chemical species, and an unprecedented horizontal resolution of 3.75° longitude by 1.875° latitude.

Simulation results reveal the presence of a nightside planetary-scale wave trapped by horizontal wind near the day-night terminator at altitudes above 105 km, while a ~5-day period Kelvin-like wave originating from below the cloud deck substantially impacts the Venusian upper atmosphere’s circulation. The Kelvin wave periodically ejects recombined molecular oxygen to high latitudes, explaining the observations of molecular oxygen airglow. Likewise, dayside atomic oxygen abundances also vary periodically, in agreement with observations of EUV oxygen airglow.

These modeling results suggest a strong, direct connection between the RZS and SS-AS layers via the Kelvin-like wave, and predict that the upper atmospheric circulation is subject to the same periodicity as this wave. This is not confirmed yet by observations of the recombination of molecular oxygen, seen in the 1.27 microns airglow, and a detailed reanalysis of existing datasets, or dedicated campaigns in future Venus missions would be very valuable to support this hypothesis of a periodicity.

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