Bondarenko M., Gavrik A. Venus - the Life cycle of 5-15km Gravity Waves: from the Upper Cloud to Extinction in the Thermosphere as Observed from Occultation Data. In: The Fifth Moscow Solar System Symposium (5MS3), October 13-18, 2014, Space Research Institute, Moscow, Russia , ab-82-83-ab.
Полный текст не доступен из этого репозитория.Аннотация
In 1983 and 1984 Soviet VENERA-15 and VENERA-16 missions conducted a large number of occultation experiments. The experimental data comprised vertical records of differential Doppler frequency and S-band (32cm) signal power which extended from 68-70km to 500 km and higher altitudes. Signals derived from these data reveal patterns identified as Gravity Waves (GWs) with wavelengths in the 5-15km range. In one “textbook” case we observed a spectacular portrait of a Gravity Wave with amplitude growth up to its breaking level just below the lower Chapman layer, resulting in perturbations comparable to the size of the second (lower) Chapman layer on the signal of power variations, with a 5.6km vertical wavelength and a typical saturated (1/x^3) spectrum. Confirmation of this interpretation and possible source of GWs of this type were sought in data from other missions to Venus and found in the 2008-2014 VEX VIRTIS instrument data (from the current joint EU Venus Express mission), which provided a horizontal view of GWs with similar parameters on UV and NI images at 61 and 66 km levels [1]. This data matches VENERA-15,16 vertical GW recordings in the vertical wavelength (5-15km) and geographicaly by the latitude bin, pointing at the possible location of the source at the upper cloud layer. More GWs with similar parameters were obtained by the VEX teams from the VIRTIS M CO2 measurements at 110-140km altitude [2]. The conflation of these three pieces of evidence forms a fuller picture and leads to a realization that occultation data, if of sufficiently high quality, may contain recordings of the whole life cycle of Gravity Waves, from generation in or near the top levels of the cloud layers to extinction in the thermosphere, i.e. at altitudes where so far the dearth of GW data has been felt. This suggests a new application of the upper ionospheric part of the occultation signal, currently routinely used only for obtaining electron density profiles in Venus studies. Next the GW data in occultation measurements were analyzed to reveal patterns of the full GW life cycle, including the (possibly multistage) process of breaking in the thermosphere, by means of time-frequency transformations. The recorded GW traces were compared to theoretical predictions (Labas, Frits 2004) [3], and good agreement was noted of the observed dissipation altitude with theory for high-frequency GWs in atmosphere with slowly changing parameters, which accounts for the effects of viscous dissipation and thermal dumping. This match was obtained with the aid of temperature and pressure profiles from SOIR data (based on spectroscopic measurements at the morning and evening terminator at altitudes between 60 and 170km) [4], which also allowed us to estimate approximate parameters of the vertically recorded GWs, such as intrinsic frequency and horizontal wavelength, confirming that VENERA-15,16 GWs and those observed horizontally by the VIRTIS instrument in the later VEX mission are of the same type, and considering the 22-30-year span between the missions, are therefore a permanent feature of the Venus atmosphere. This approach suggests that occultations could serve as another remote sensing technique for the study of GWs at levels up to their breaking at the turbopause altitudes, with time-frequency transforms acting “as an analogue of the Wilson chamber” (or cloud chamber) of the early particle physics, to reveal traces of the GW growth and dissipation. This application should be relevant to environments other than Venus atmosphere, if occultation signals of sufficiently high quality are available. Relevance of the proposed method to the uncovering of similar information from the VEX VeRa occultation data was also discussed. This work was partially supported by Program No 22 of the Presidium of the Russian Academy of Science.
| Тип объекта: | Доклад на конференции или семинаре (Доклад) |
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| Авторы на русском. ОБЯЗАТЕЛЬНО ДЛЯ АНГЛОЯЗЫЧНЫХ ПУБЛИКАЦИЙ!: | Бондаренко М.И., Гаврик А.Л. |
| Подразделения (можно выбрать несколько, удерживая Ctrl): | 119 лаб. распространения радиоволн и дистанционного зондирования атмосферы |
| URI: | http://cplire.ru:8080/id/eprint/1882 |
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