Physics
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf..116p&link_type=abstract
European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a
Physics
Scientific paper
Venus mesosphere (60 - 100 km altitude) is a transition region between two dynamical regimes: a retrograde super-rotation dominates in the troposphere and mesosphere with wind speed of up to 120 m/s near the cloud top (~70 km), while solar-antisolar circulation dominates in the thermosphere. Earlier studies [1], [2], [3] have proved that the strong zonal winds near the cloud top are well described by the thermal wind equation, which directly relates the zonal winds to the mesospheric temperature field. The thermal wind equation is obtained assuming the cyclostrophic approximation, which consists in the balance between the equatorward component of the centrifugal force and the poleward component of the pressure gradient force. VIRTIS (Visible and Infrared Thermal Imaging Spectrometer) on board Venus Express is investigating the thermal structure of Venus mesosphere for more than 2 years with a very good spatial and temporal coverage of Venus' south hemisphere. Here we present the retrievals of cyclostrophic winds from VIRTIS - M temperature profiles. Our retrieved zonal winds show three important features: a midlatitude jet connected to the cold collar located at the cloud top around 50° latitude with a speed of 90 ± 10 m/s; a fast decrease of wind speed from 50° latitude towards the pole; and a gradual decrease of wind speed with height above the cloud tops [4]. Preliminary analysis shows only weak dependence of zonal winds on local time. Comparison of the thermal wind with cloud tracked winds measured by VMC (Venus Monitoring Camera) show general good agreement at middle and high latitudes and disagreement at low latitudes [5]. References [1] Newman, M. et al. (1984) J. of Atm. Sciences, 41, 1901-1913. [2] Roos-Serote, M. et al. (1994) Icarus, 114(2), 300- 309. [3] Zasova, L. V. and I. V. Khatuntsev (1997) Adv. Space Res., 19(8), 1181-1190. [4] Piccialli, A. et al. (2008) J. Geophys. Res., (submitted). [5] Moissl, R. R. et al. (2008) J. Geophys. Res., (submitted).
Drossart Pierre
Grassi Daniele
Khatuntsev Igor
Migliorini Alessandra
Piccialli Arianna
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