Atmospheric dynamics at the southern pole of Venus: Three-dimensional winds, temperature and vorticity

Abstract:

The atmospheric vortex at the southern pole of Venus is a complex structure well observed over the Venus Express mission. The vortex is highly variable in morphology exhibiting large-scale transitions with time scales of a few days. In order to better understand the relation between the vortex’s morphology and its dynamics, we measure the wind field at the lower and upper clouds levels (at ~43 km and ~59 km, respectively) and retrieve the three-dimensional thermal structure of the polar atmosphere using data from the infrared channel of the instrument VIRTIS on board Venus Express.

Combining wind and temperature fields we calculate the horizontal spatial structure of Ertel’s potential vorticity (EPV) at both clouds levels. Our analysis shows that the South Polar Vortex of Venus is a vertically depressed structure when observed in isentropic surfaces between 55 and 85 km altitude, and that the horizontal distribution of EPV does not retain the structure seen in radiance or temperature maps, but resembles the distribution of the relative vorticity (determined purely from tracked motions).

With the temperature profiles at hand, we calculate the thermal winds over the south polar atmosphere of Venus by means of the cyclostrophic approximation. We improve the method to retrieve the thermal winds at high latitudes (so far inconsistent with cloud tracking measurements [1, 2]) by taking into account the meridional component of the wind to fully explore the three-dimensional structure of the vortex in the upper troposphere.

[1] Mendonça, J. M., Read, P. L., Wilson, C. F., & Lewis, S. R. (2012). Zonal winds at high latitudes on Venus: An improved application of cyclostrophic balance to Venus Express observations. Icarus, 217, 629–639. doi:10.1016/j.icarus.2011.07.010

[2] Piccialli, A., Tellmann, S., Titov, D. V., Limaye, S. S., Khatuntsev, I. V., Pätzold, M., & Häusler, B. (2012). Dynamical properties of the Venus mesosphere from the radio-occultation experiment VeRa onboard Venus Express. Icarus, 217 (2), 669–681. doi:10.1016/j.icarus.2011.07.016