Small-scale temperature fluctuations seen by the VeRa Radio Science Experiment on Venus Express

• Published in: Icarus (New York, N.Y. 1962) N.Y. 1962), 2012-11, Vol.221 (2), p.471-480
• Main Authors: Tellmann, S., Häusler, B., Hinson, D.P., Tyler, G.L., Andert, T.P., Bird, M.K., Imamura, T., Pätzold, M., Remus, S.
• Format: Article
• Language: English
• Subjects: Amplitudes; Astronomy; Atmospheres, Dynamics; Atmospherics; Earth, ocean, space; Exact sciences and technology; Gravity waves; Horizontal; Latitude; Occultations; Radio observations; Small scale; Solar system; Venus; Wavelengths
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2012.08.023

► Vertical small scale temperature perturbations in the Venus atmosphere are studied. ► Gravity wave activity is significantly enhanced above the tropopause. ► The low latitude range displays the lowest wave amplitudes. ► The greatest gravity wave activity is found in the high northern latitudes west of Ishtar Terra. ► The wave activity in the equatorial region has maxima in the early afternoon. The Venus Express Radio Science Experiment VeRa retrieves atmospheric profiles in the mesosphere and troposphere of Venus in the approximate altitude range of 40–90km. A data set of more than 500 profiles was retrieved between the orbit insertion of Venus Express in 2006 and the end of occultation season No. 11 in July 2011. The atmospheric profiles cover a wide range of latitudes and local times, enabling us to study the dependence of vertical small-scale temperature perturbations on local time and latitude. Temperature fluctuations with vertical wavelengths of 4km or less are extracted from the measured temperature profiles in order to study small-scale gravity waves. Significant wave amplitudes are found in the stable atmosphere above the tropopause at roughly 60km as compared with the only shallow temperature perturbations in the nearly adiabatic region of the adjacent middle cloud layer, below. Gravity wave activity shows a strong latitudinal dependence with the smallest wave amplitudes located in the low-latitude range, and an increase of wave activity with increasing latitude in both hemispheres; the greatest wave activity is found in the high-northern latitude range in the vicinity of Ishtar Terra, the highest topographical feature on Venus. We find evidence for a local time dependence of gravity wave activity in the low latitude range within ±30° of the equator. Gravity wave amplitudes are at their maximum beginning at noon and continuing into the early afternoon, indicating that convection in the lower atmosphere is a possible wave source. The comparison of the measured vertical wave structures with standard linear-wave theory allows us to derive rough estimates of the wave intrinsic frequency and horizontal wavelengths, assuming that the observed wave structures are the result of pure internal gravity waves. Horizontal wavelengths of the waves at 65km altitude are on the order of ≈300–450km with horizontal phase speeds of roughly 5–10m/s.