Dynamics of the Venus atmosphere is still an unsolved fundamental problem in the planetary physics. ESA’s Venus Express collected long imaging time series in several wavelengths from UV to near-IR. It was later complemented by JAXA’s Akatsuki observations, thus providing the longest almost uninterrupted monitoring of the Venus atmosphere dynamics for about 26 Venus years. Tracking of cloud features allowed determination of wind speed at different levels within the cloud deck thus enabling significant progress in characterization of the mean atmospheric circulation. The analysis revealed wind variability including changes with altitude, latitude, local solar time as well as influence of the surface topography and long term 12.5 years periodicity.The images also provided morphological evidences of dynamical processes at the cloud level. UV dark low latitudes were found to be dominated by convective mixing that brings UV absorbers from depth, while bright uniform clouds at middle-to-high latitudes are typical for the regions with suppresses vertical mixing. The latter feature correlates with drastic increase of the total cloud opacity poleward from ~60° latitude that likely indicates presence of a dynamical mixing barrier here. Similarity of the global UV cloud morphology at the cloud top (~70 km) and that in the deep cloud (50-55 km) observed in the near-IR on the night side suggested similar morphology shaping processes throughout the cloud deck. Venus Express observed gravity waves poleward of 65°N concentrated at the edges of Ishtar Terra likely indicating their generation by wind interaction with the surface. Venus Express performed about 800 radio occultations providing precise measurements of the atmospheric temperature structure and static stability parameter in the altitude range 40-90 km. The Richardson number latitude-altitude field derived from the wind and temperature measurements suggests presence of convection in the cloud deck and stable mesosphere above it with the convective layer extending to greater depth at high latitudes. The talk will present recent results on the atmospheric circulation, supplemented by a summary of the Venus Express observations related to the atmospheric dynamics and an outlook for further analysis of these data.

Серии последовательных УФ-изображений (365 нм) облачного покрова Венеры позволяют исследовать динамику мезосферы. Беспрецедентный по продолжительности ряд таких изображений получен камерами VMC на борту космического аппарата (КА) Venus Express (ESA) и UVI на борту КА Akatsuki (JAXA) c 2006 по 2022 гг. На 10° ю. ш. наблюдаются долговременные изменения средней зональной и меридиональной скоростей ветра с периодом 12.5 ± 0.5 лет. Анализ поведения среднего зонального ветра около полудня 12 ± 1 ч. при фазовых углах 60°–90° в ограниченные по времени интервалы наблюдения показывает, что вблизи минимума долгопериодической зависимости торможение горизонтального потока наблюдается над областью Овды, наиболее высокой частью Земли Афродиты, как для VMC, так и для UVI. И наоборот, ускорение наблюдается над областью Овды вблизи максимума долгопериодической зависимости. Рассматриваемые долготные вариации зональной скорости простираются от экватора до средних широт (0°–40°). Меридиональная скорость показывает долготные вариации, связанные с рельефом подстилающей поверхности, вне зависимости от того, торможение или ускорение горизонтального потока наблюдается над высокогорной частью Земли Афродиты.

Series of consecutive UV (365 nm) images of Venus cloud coverage provide a way to investigate dynamics of the mesosphere. An unprecedented series of such images was obtained by the VMC/Venus Express (ESA) and UVI/Akatsuki (JAXA) cameras from 2006 to 2022. At 10°S long-term variations in the mean zonal and meridional wind speed are observed with a period of 12.5 ± 0.5 years. Analysis of the of the mean zonal wind behavior around noon (12 ± 1 h) at phase angles of 60°–90° in limited observation time intervals shows that near the minimum of the long-term dependence the deceleration of the horizontal flow is observed above the highest part of Aphrodite Terra, Ovda Regio, for both VMC and UVI. Conversely, acceleration is observed above the Ovda Regio near the maximum of the long-term dependence. The considered longitudinal variations of the zonal wind speed extend from the equator to middle latitudes (0°–40°). The meridional wind speed shows longitudinal variations associated with the topography of the underlying surface, regardless of whether the horizontal flow is slowing down or accelerating above the highlands of Aphrodite Terra.

This research studies the O 2 (a 1 Δ g ) nightglow distribution in 1.27 μm to understand the dynamics of the atmosphere of Venus. Several factors were considered in the retrieval process, such as thermal emission of the lower atmosphere, reflection by the clouds. Results show deviation from SS-AS circulation mode: the area where horizontal flows from the dayside converge and where oxygen recombines and emits shifts from the midnight to 22–23 hours local time. This shift is caused by solar-induced thermal tide on Venus nightside. Some conclusions about the upper mesosphere dynamics are also presented.

We present joint analysis of the UV (365 nm) images captured by the cameras on board ESA’s Venus Express and JAXA’s Akatsuki spacecraft. These observations enabled almost continuous characterization of the cloud top circulation over the longest period of time so far (2006–2021). More than 46,000 wind vectors were derived from tracking the UV cloud features and revealed changes in the atmospheric circulation with the period of 12.5 ± 0.5 years. The zonal wind component is characterized by an annual mean of −98.6 ± 1.3 m/s and an amplitude of 10.0 ± 1.6 m/s. The mean meridional wind velocity is −2.3 ± 0.2 m/s and has an amplitude of 3.4 ± 0.3 m/s. Plausible physical explanations of the periodicity include both internal processes and external forcing. Both missions observed periodical changes in the UV albedo correlated with the circulation variability. This could result in acceleration or deceleration of the winds due to modulation of the deposition of the radiative energy in the clouds. The circulation can be also affected by the solar cycle that has a period of approximately 11 years with a large degree of deviation from the mean. The solar cycle correlated with the wind observations can probably influence both the radiative balance and chemistry of the mesosphere. The discovered periodicity in the cloud top circulation of Venus, and especially its similarity with the solar cycle, is strongly relevant to the study of exoplanets in systems with variable “suns”.

Wind vectors derived by processing data of UV (365 nm) images obtained by Venus Monitoring Camera (VMC) onboardVenus Express spacecraft from 2006 to 2013 and by Ultraviolet Imager (UVI) onboard Akatsuki from 2016 to 2019 wereused to study mesosphere dynamics. We found that the trend of the mean zonal wind speed at South equatorial latitudesof Venus changed from upward to downward in time period from 2014 to 2015. Analysis of the longitudinal dependence ofthe average zonal velocity, obtained from both the VMC and the UVI data, reveals decrease in wind speed associated withAphrodite Terra.

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.

The horizontal wind velocity vectors at the lower cloud layer were retrieved by tracking the displacement of cloud features using the 1.74 µm images of the full Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS-M) dataset. This layer was found to be in a superrotation mode with a westward mean speed of 60–63 m s−1 in the latitude range of 0–60° S, with a 1–5 m s−1 westward deceleration across the nightside. Meridional motion is significantly weaker, at 0–2 m s−1; it is equatorward at latitudes higher than 20° S, and changes its direction to poleward in the equatorial region with a simultaneous increase of wind speed. It was assumed that higher levels of the atmosphere are traced in the equatorial region and a fragment of the poleward branch of the direct lower cloud Hadley cell is observed. The fragment of the equatorward branch reveals itself in the middle latitudes. A diurnal variation of the meridional wind speed was found, as east of 21 h local time, the direction changes from equatorward to poleward in latitudes lower than 20° S. Significant correlation with surface topography was not found, except for a slight decrease of zonal wind speed, which was connected to the volcanic area of Imdr Regio.

In this paper, we consider the implementation of the "cloud" computing strategy to study data sets associated to the atmospheric exploration of the planet Venus. More concretely, the Venus Monitoring Camera (VMC) onboard Venus Express orbiter provided the largest and the longest so far set of ultraviolet (UV), visible and near-IR images for investigation of the atmospheric circulation. To our best knowledge, this is the first time where the analysis of data from missions to Venus is integrated in the context of the "cloud" computing. The followed path and protocols can be extended to more general cases of space data analysis, and to the general framework of the big data analysis.

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.

For more than 8years the Venus Monitoring Camera (VMC) onboard the Venus Express orbiter performed continuous imaging of the Venus cloud layer in UV, visible and near-IR filters. We applied the correlation approach to sequences of the near-IR images at 965nm to track cloud features and determine the wind field in the middle and lower cloud (49-57km). From the VMC images that spanned from December of 2006 through August of 2013 we derived zonal and meridional components of the wind field. In low-to-middle latitudes (5-65 degrees S) the velocity of the retrograde zonal wind was found to be 68-70m/s. The meridional wind velocity slowly decreases from peak value of +5.81.2m/s at 15 degrees S to 0 at 65-70 degrees S. The mean meridional speed has a positive sign at 5-65 degrees S suggesting equatorward flow. This result, together with the earlier measurements of the poleward flow at the cloud tops, indicates the presence of a closed Hadley cell in the altitude range 55-65km. Long-term variations of zonal and meridional velocity components were found during 1,200 Earth days of observation. At 20 degrees 5 degrees S the zonal wind speed increases from -67.181.81m/s to -77.302.49m/s. The meridional wind gradually increases from +1.30 +/- 1.82m/s to +8.53 +/- 2.14m/s. Following Bertaux et al. (2016) we attribute this long-term trend to the influence from the surface topography on the dynamical process in the atmosphere via the upward propagation of gravity waves that became apparent in the VMC observations due to slow drift of the Venus Express orbit over Aphrodite Terra.

Based on the analysis of UV images (at 365 nm) of Venus cloud top (altitude 67±2 km) collected with VMC (Venus Monitoring Camera) on board Venus Express (VEX), it is found that the zonal wind speed south of the equator (from 5◦S to 15◦s) shows a conspicuous variation (from -101 to -83 m/s) with geographic longitude of Venus, correlated with the underlying relief of Aphrodite Terra. We interpret this pattern as the result of stationary gravity waves produced at ground level by the up lift of air when the horizontal wind encounters a mountain slope. These waves can propagate up to cloud top level, break there and transfer their momentum to the zonal flow. Such upward propagation of gravity waves and influence on the wind speed vertical profile was shown to play an important role in the middle atmosphere of the Earth by Lindzen [1981], but is not reproduced in a current GCM of Venus atmosphere. Consistent with present findings, the two VEGA mission balloons experienced a small, but significant, difference of westward velocity, at their 53 km floating altitude. The albedo at 365 nm varies also with longitude and latitude in a pattern strikingly similar in the low latitude regions to a recent map of cloud top H2O [Fedorova et al., 2015], in which a lower UV albedo is correlated with increased H2O. We argue that H2O enhancement is the sign of upwelling, suggesting that the UV absorber is also brought to cloud top by upwelling.

The Venus Monitoring Camera (VMC) acquired a set of ultraviolet (UV) images during the Venus Express mission unprecedented in its duration from May 2006 to September 2013. Here we present the results of digital tracking of the cloud features in the upper cloud layer at latitudes 25–75°S using images from 257 orbits with the best spatial coverage. The method relies on analysis of correlations between pairs of UV images separated in time. The bulk of data processed allows us to clarify the reasons why the mid-latitude jet is not always present in latitudinal wind profiles. Comparing VMC images with wind velocity fields we found a relationship between cloud morphology at middle latitudes and the circulation. The vector field in middle latitudes depends on the presence of a contrast global streak in the cloud morphology tilted with respect to latitude circles. The angle of the flow deflection (the angle between the wind velocity and latitudinal circles) and the difference of the zonal velocity on the opposite sides of the streak are in direct relationship to the angle between the streak and latitude circles. During such orbits the jet bulge does not appear in the latitudinal profile of the zonal wind component. Otherwise a zonal flow with small changes of the meridional velocity dominates in middle latitudes and manifests itself as a jet bulge. The relationship between the cloud cover morphology and circulation peculiarities can be attributed to the motion of global cloud features, like the Y-feature. We prepared plots of zonal and meridional velocities averaged with respect to the entire observation period. The average zonal velocity has a diurnal maximum at 15:00 local solar time and at 40°S. The meridional velocity reaches its maximum between 13:00 and 16:00 and at 50°S. The velocities obtained by the digital method are in good agreement with results of the visual method in the middle latitudes published earlier by Khatuntsev et al. (2013).

Six years of continuous monitoring of Venus by European Space Agency's Venus Express orbiter provides an opportunity to study dynamics of the atmosphere our neighbor planet. Venus Monitoring Camera (VMC) on-board the orbiter has acquired the longest and the most complete so far set of ultra violet images of Venus. These images enable a study the cloud level circulation by tracking motion of the cloud features. The highly elliptical polar orbit of Venus Express provides optimal conditions for observations of the Southern hemisphere at varying spatial resolution. Out of the 2300 orbits of Venus Express over which the images used in the study cover about 10 Venus years. Out of these, we tracked cloud features in images obtained in 127 orbits by a manual cloud tracking technique and by a digital correlation method in 576 orbits. Total number of wind vectors derived in this work is 45,600 for the manual tracking and 391,600 for the digital method. This allowed us to determine the mean circulation, its long-term and diurnal trends, orbit-to-orbit variations and periodicities. We also present the first results of tracking features in the VMC near-IR images. In low latitudes the mean zonal wind at cloud tops (67 +/- 2 km following: Rossow, W.B., Del Genio, A.T., Eichler, T. [1990]. J. Atmos. Sci. 47,2053-2084) is about 90 m/s with a maximum of about 100 m/s at 40-50 degrees S. Poleward of 50 degrees S the average zonal wind speed decreases with latitude. The corresponding atmospheric rotation period at cloud tops has a maximum of about 5 days at equator, decreases to approximately 3 days in middle latitudes and stays almost constant poleward from 50 degrees S. The mean poleward meridional wind slowly increases from zero value at the equator to about 10 m/s at 50 degrees S and then decreases to zero at the pole. The error of an individual measurement is 7.5-30 m/s. Wind speeds of 70-80 m/s were derived from near-IR images at low latitudes. The VMC observations indicate a long term trend for the zonal wind speed at low latitudes to increase from 85 m/s in the beginning of the mission to 110 m/s by the middle of 2012. VMC UV observations also showed significant short term variations of the mean flow. The velocity difference between consecutive orbits in the region of mid-latitude jet could reach 30 m/s that likely indicates vacillation of the mean flow between jet-like regime and quasi-solid body rotation at mid-latitudes. Fourier analysis revealed periodicities in the zonal circulation at low latitudes. Within the equatorial region, up to 35 degrees S, the zonal wind show an oscillation with a period of 4.1-5 days (4.83 days on average) that is close to the super-rotation period at the equator. The wave amplitude is 4-17 m/s and decreases with latitude, a feature of the Kelvin wave. The VMC observations showed a clear diurnal signature. A minimum in the zonal speed was found close to the noon (11-14 h) and maxima in the morning (8-9 h) and in the evening (16-17 h). The meridional component peaks in the early afternoon (13-15 h) at around 50 degrees S latitude. The minimum of the meridional component is located at low latitudes in the morning (8-11 h). The horizontal divergence of the mean cloud motions associated with the diurnal pattern suggests upwelling motions in the morning at low latitudes and downwelling flow in the afternoon in the cold collar region. (C) 2013 Elsevier Inc. All rights reserved.