Winds derived by a digital tracking technique from ultraviolet (365 nm) images captured by the Venus Monitoring Camera (VMC) onboard the Venus Express spacecraft from 2006 to 2013 were used to study ...the atmospheric circulation at cloud top level (70 ± 2 km). This data set allows variations of the wind speed with both latitude and longitude to be studied and establishes their correlation with surface topography as well as local time dependence. Both zonal and meridional wind components show some correlation with topography. The minimum zonal wind speed was found at noon above Ovda Regio (10°S, 93°E), the highest region of Aphrodite Terra, one of the largest highlands in the equatorial region. The area of slow zonal wind extends to at least 30°S and shifts in the direction of superrotation in the afternoon and with increasing latitude (poleward). The observed deceleration of cloud top wind was recently attributed to the interaction of the gravity (mountain) waves generated by Aphrodite Terra with the atmospheric circulation. The present study was performed for different local time over the mountainous longitudes. The deceleration pattern in the zonal wind field is mainly conserved within a few hours around noon. Systematic longitude shift is observed in the afternoon in the direction of the evening terminator. Another area of perturbation of both zonal and meridional wind components is observed in the equatorial region around LT = 13–14 hr and may be explained by the solar tide.
Plain Language Summary
Venus is completely covered with a thick cloud layer with its top at about 70 km. Surprisingly, recent observations show that the cloud level circulation is affected by the surface topography. In this paper we analyzed wind velocities derived from tracking of cloud features in the UV images acquired by the Venus Monitoring Camera onboard the European Space Agency's Venus Express orbiter during its operations from 2006 to 2013. The zonal wind at the cloud top decelerates by about 20% above the highest part of Aphrodite Terra and reaches its minimum at local noon. The zonal wind deceleration is explained by interaction of gravity waves generated by the surface relief with the atmospheric circulation. An additional deceleration occurs in the afternoon in the equatorial region and is probably caused by solar heating of the clouds. The combination of both effects results in a vast area of slow wind during the daytime.
Key Points
A maximum deceleration of the mean zonal flow is observed at noon above the highest region of Aphrodite Terra, Venus
The mean zonal and meridional flows at cloud top level in the equatorial region are perturbed by a solar tide at 13–14 hr
A dependence of the mean zonal and meridional flows on topography is observed from the equator to at least 30°S
We present more than 250,000 wind vectors derived from the visible (513 nm) images captured by the Venus Monitoring Camera (VMC) onboard ESA's Venus Express orbiter in the Southern hemisphere from 01 ...July 2007 to 29 January 2013. From comparison to the wind velocity derived from tracking of the descent probes, these measurements correspond to 60 ± 3 km altitude, being between two levels 70 ± 2 km and 55 ± 2 km, probed by VMC in ultraviolet (UV) (365 nm) and NIR (965 nm) channels, respectively. The mean zonal wind suggests retrograde circulation with mean zonal wind speed decreasing from 76.5 to 61.5 m/s at 30°–65°S. In low latitudes, 10–20°S, it increased to 82 m/s over the course of the mission. The mean zonal flow depends on local solar time and latitude and is affected by the large‐scale topography. The meridional winds indicated equatorward flow of up to 7 m/s in the middle and low cloud opposite to that derived from simultaneous UV observations at the cloud top.
Plain Language Summary
Dynamics of the Venus atmosphere is dominated by a strong zonal retrograde circulation called “superrotation.” The physical mechanisms maintaining this unique regime are poorly understood due to insufficient observational data. For about eight years, the Venus Monitoring Camera onboard ESA's Venus Express orbiter monitored motions of the cloud features in three spectral ranges: ultraviolet (UV) (365 nm), visible (513 nm), and near‐infrared (915 nm). These wavelengths probed different altitudes: 70 ± 2 km, 60 ± 3 km, and 55 ± 2 km correspondingly, thus providing wind field tomography. In this paper, we present more than 250,000 wind vectors derived from the visible images. The results suggest decrease of the retrograde mean zonal wind speed from 76.5 to 61.5 m/s at 30°–65°S, and its increase up to 82 m/s at 10–20°S and show pronounced variations with local solar time, latitude, and surface topography. Interestingly, the meridional winds indicate equatorward flow of up to 7 m/s in the deep cloud opposite to that previously derived from UV images at the cloud top.
Key Points
More than 250,000 wind vectors at 57–63 km altitude were derived from the images taken by the Venus Monitoring Camera /Venus Express visible (513 nm) channel
Mean zonal wind speed accelerated by ∼18.5 m/s at 30 ± 5°S over 8 Venusian years
Zonal wind speed decreased from 85 m/s at the equator to 35 m/s at 80°S, meridional wind of up to 7 m/s velocity is directed equatorward
The paper is devoted to the investigation of Venus mesosphere circulation at 90–110 km altitudes, where tracking of the O2(a1Δg) 1.27 μm nightglow is practically the only method of studying the ...circulation. The images of the nightglow were obtained by VIRTIS‐M on Venus Express over the course of more than 2 years. The resulting global mean velocity vector field covers the nightside between latitudes 75°S–20°N and local time 19–5 h. The main observed mode of circulation is two opposite flows from terminators to midnight; however, the wind speed in the eastward direction from the morning side exceeds the westward (evening) by 20–30 m/s, and the streams “meet” at 22.5 ± 0.5 h. The influence of underlying topography was suggested in some cases: Above mountain regions, flows behave as if they encounter an “obstacle” and “wrap around” highlands. Instances of circular motion were discovered, encompassing areas of 1,500–4,000 km.
Plain Language Summary
Recent developments in the studies of Venus atmosphere reveal an intriguing phenomenon of stationary gravity waves, which emerge from the surface, interacting with the cloud layer up to ~70 km. In this paper, analysis of the oxygen nightglow on the nightside of Venus using data from VIRTIS instrument (Venus Express spacecraft) delivers clues that the atmosphere at 90–110 km altitude can as well be influenced by such mechanisms. The horizontal motion, obtained from tracking the displacements of the bright features of the nightglow, appears to hold disturbances, the positions of which in some cases coincide with highlands directly below or shifted by several degrees. The nightglow itself, known to manifest an extremely irregular behavior, sometimes repeats the shapes of the mountain ranges below. As another major result, the mean horizontal circulation, calculated for the nightside southern hemisphere, does represent neither superrotation, nor subsolar‐to‐antisolar circulation, nor a superposition of the two. Both the zonal and the meridional components of the motion have different magnitudes and direction before and after midnight. The results of this research further our knowledge on the upper atmosphere of Venus and pose a challenge for the global circulation models.
Key Points
The horizontal wind velocity in Venus atmosphere at 90–110 km was obtained from the O2(a1Δg) nightglow tracking
Average zonal component from the morning side exceeds its opposite from the evening side by 20–30 m/s; they “meet” at 22–23 h local time
The influence of the underlying topography on the wind direction was suggested in some cases
The mapping IR channel of the Visual and Infrared Thermal Imaging Spectrometer (VIRTIS‐M) on board the Venus Express spacecraft observes the CO2 band at 4.3 μm at a spectral resolution adequate to ...retrieve the atmospheric temperature profiles in the 65–96 km altitude range. Observations acquired in the period June 2006 to July 2008 were used to derive average temperature fields as a function of latitude, subsolar longitude (i.e., local time, LT), and pressure. Coverage presented here is limited to the nighttime because of the adverse effects of daytime non‐LTE emission on the retrieval procedure and to southernmost latitudes because of the orientation of the Venus‐Express orbit. Maps of air temperature variability are also presented as the standard deviation of the population included in each averaging bin. At the 100 mbar level (about 65 km above the reference surface), temperatures tend to decrease from the evening to the morning side despite a local maximum observed around 20–21LT. The cold collar is evident around 65S, with a minimum temperature at 3LT. Moving to higher altitudes, local time trends become less evident at 12.6 mbar (about 75 km) where the temperature monotonically increases from middle latitudes to the southern pole. Nonetheless, at this pressure level, two weaker local time temperature minima are observed at 23LT and 2LT equatorward of 60S. Local time trends in temperature reverse about 85 km, where the morning side is the warmer. The variability at the 100 mbar level is maximum around 80S and stronger toward the morning side. Moving to higher altitudes, the morning side always shows the stronger variability. Southward of 60S, standard deviation presents minimum values around 12.6 mbar for all the local times.
Structure of the Venus atmosphere Zasova, L.V.; Ignatiev, N.; Khatuntsev, I. ...
Planetary and space science,
10/2007, Letnik:
55, Številka:
12
Journal Article
Recenzirano
The structure of the Venus atmosphere is discussed. The data obtained in the 1980s by the last Soviet missions to Venus: orbiters Venera 15, 16 and the entry probes and balloons of Vega 1 and 2 are ...compared with the Venus International Reference Atmosphere (VIRA) model. VIRA is based on the data of the extensive space investigations of Venus in the 1960s and 1970s. The results of the IR Fourier Spectrometry experiment on Venera 15 are reviewed in detail. This instrument is considered as a precursor of the long wavelength channel of the Planetary Fourier Spectrometer on Venus Express.
We consider the concept of applying gravity assist maneuvers near Venus using resonant orbits with a period equal to the Venusian one. We show that the proposed operations based on this concept allow ...the reachable landing areas on the surface of Venus to be expanded radically. The price of this approach is an increase of the time interval needed to solve this problem by a value equal to the orbital period of Venus. The cost of the characteristic velocity in this case remains within limits close to the standard variants of planning missions to Venus.
We present here methods developed for the retrieval of air temperature profiles in the Venusian mesosphere from the absolute radiances measured by the Visual and Infrared Thermal Imaging Spectrometer ...(VIRTIS) on board the Venus Express satellite. The infrared M channel of the instrument acquires multispectral images between 1000 and 5000 nm. In nighttime measurements, radiance in the range 3800–5000 nm is dominated by the thermal emission and absorption by the clouds and carbon dioxide. Since the latter is the main atmospheric component, it is possible to exploit the strong variability of its opacity in this spectral range, as resolved by the instrument, to reconstruct the vertical air temperature profile as a function of pressure. In this context we decided to adopt the Twomey et al. (1977) relaxation scheme. The resulting code was extensively tested on a set of simulated VIRTIS‐M data. Comparison of the known input conditions with the results of analysis code allowed us to evaluate the systematic and random errors affecting the retrievals procedures on a statistical basis. The code returns the vertical air temperature profile with an uncertainty of less than 1 K in the region between 70 and 7 mbar (66 and 77 km above the reference surface) and less than 4 K throughout the entire range 100–0.1 mbar (64–95 km). Finally, we present the first examples of the code applied to actual measured Venusian data, demonstrating its capability to achieve a satisfactory modeling of the observations and provide physically reasonable results.
Abstract
The paper is devoted to the investigation of Venus mesosphere circulation at 90–110 km altitudes, where tracking of the O
2
(a
1
Δ
g
) 1.27 μm nightglow is practically the only method of ...studying the circulation. The images of the nightglow were obtained by VIRTIS‐M on Venus Express over the course of more than 2 years. The resulting global mean velocity vector field covers the nightside between latitudes 75°S–20°N and local time 19–5 h. The main observed mode of circulation is two opposite flows from terminators to midnight; however, the wind speed in the eastward direction from the morning side exceeds the westward (evening) by 20–30 m/s, and the streams “meet” at 22.5 ± 0.5 h. The influence of underlying topography was suggested in some cases: Above mountain regions, flows behave as if they encounter an “obstacle” and “wrap around” highlands. Instances of circular motion were discovered, encompassing areas of 1,500–4,000 km.
Plain Language Summary
Recent developments in the studies of Venus atmosphere reveal an intriguing phenomenon of stationary gravity waves, which emerge from the surface, interacting with the cloud layer up to ~70 km. In this paper, analysis of the oxygen nightglow on the nightside of Venus using data from VIRTIS instrument (Venus Express spacecraft) delivers clues that the atmosphere at 90–110 km altitude can as well be influenced by such mechanisms. The horizontal motion, obtained from tracking the displacements of the bright features of the nightglow, appears to hold disturbances, the positions of which in some cases coincide with highlands directly below or shifted by several degrees. The nightglow itself, known to manifest an extremely irregular behavior, sometimes repeats the shapes of the mountain ranges below. As another major result, the mean horizontal circulation, calculated for the nightside southern hemisphere, does represent neither superrotation, nor subsolar‐to‐antisolar circulation, nor a superposition of the two. Both the zonal and the meridional components of the motion have different magnitudes and direction before and after midnight. The results of this research further our knowledge on the upper atmosphere of Venus and pose a challenge for the global circulation models.
Key Points
The horizontal wind velocity in Venus atmosphere at 90–110 km was obtained from the O
2
(a
1
Δ
g
) nightglow tracking
Average zonal component from the morning side exceeds its opposite from the evening side by 20–30 m/s; they “meet” at 22–23 h local time
The influence of the underlying topography on the wind direction was suggested in some cases
We discuss a change in the resurfacing regimes of Venus and probable ways of forming the terrain types that make up the surface of the planet. The interpretation of the nature of the terrain types ...and their morphologic features allows us to characterize their scientific priority and the risk of landing on their surface to be estimated. From the scientific point of view, two terrain types are of special interest and represent easily achievable targets: the lower unit of regional plains and the smooth plains associated with impact craters. Regional plains are probably a melting from the upper fertile mantle. The material of smooth plains of impact origin is a well-mixed and representative sample of the Venusian crust. The lower unit of regional plains is the most widespread one on the surface of Venus, and it occurs within the boundaries of all of the precalculated approach trajectories of the lander. Smooth plains of impact origin are crossed by the approach trajectories precalculated for 2018 and 2026.
The recently selected missions to Venus have opened a new era for the exploration of this planet. These missions will provide information about the chemistry of the atmosphere, the geomorphology, ...local-to-regional surface composition, and the rheology of the interior. One key scientific question to be addressed by these future missions is whether Venus remains volcanically active, and if so, how its volcanism is currently evolving. Hence, it is fundamental to analyze appropriate terrestrial analog sites for the study of possibly active volcanism on Venus. To this regard, we propose Mount Etna - one of the most active and monitored volcanoes on Earth - as a suitable terrestrial laboratory for remote and in-situ investigations to be performed by future missions to Venus. Being characterized by both effusive and explosive volcanic products, Mount Etna offers the opportunity to analyze multiple eruptive styles, both monitoring active volcanism and identifying the possible occurrence of pyroclastic activity on Venus. We directly compare Mount Etna with Idunn Mons, one of the most promising potentially active volcanoes of Venus. Despite the two structures show a different topography, they also show some interesting points of comparison, and in particular: a) comparable morpho-structural setting, since both volcanoes interact with a rift zone, and b) morphologically similar volcanic fields around both Mount Etna and Idunn Mons. Given its ease of access, we also propose Mount Etna as an analog site for laboratory spectroscopic studies to identify the signatures of unaltered volcanic deposits on Venus.
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