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![(a) Mean direction of the meridional wind at different altitudes (arrows) overlaid on the thermal structure of the atmosphere in latitude-altitude coordinates from combined Venus Express and Akatsuki radio occultation experiment results, averaged over both hemispheres [30]. We changed the latitude sign to negative to adopt the figure to the Southern hemisphere. Numbers at the contours indicate the temperature in Kelvin. Latitudes represent both hemispheres assuming north-south symmetry. The thermal structure is used for illustration to designate different levels in the Southern Hemisphere. Blue arrows represent UV cloud tracking results (PV and VMC/VEX), red arrow: IR cloud tracking from VMC/VEX, green arrows: 1.74 µm (1740 nm) IR cloud tracking from VIRTIS/VEX. Dashed green arrows indicate branches of Hadley cells that are not observable in the experiment. (b) Mean latitudinal profiles of the meridional wind from several experiments; line colors correspond with those in (a), line types correspond with the legend. Two vertical lines located at v = 0 axis limit the latitude range of the 1.74 µm cloud tracking profile (green line) where the meridional wind becomes south-poleward.](publication/348909270/figure/fig6/AS:1023817753317379@1621108582605/a-Mean-direction-of-the-meridional-wind-at-different-altitudes-arrows-overlaid-on-the.png)
(a) Mean direction of the meridional wind at different altitudes (arrows) overlaid on the thermal structure of the atmosphere in latitude-altitude coordinates from combined Venus Express and Akatsuki radio occultation experiment results, averaged over both hemispheres [30]. We changed the latitude sign to negative to adopt the figure to the Southern hemisphere. Numbers at the contours indicate the temperature in Kelvin. Latitudes represent both hemispheres assuming north-south symmetry. The thermal structure is used for illustration to designate different levels in the Southern Hemisphere. Blue arrows represent UV cloud tracking results (PV and VMC/VEX), red arrow: IR cloud tracking from VMC/VEX, green arrows: 1.74 µm (1740 nm) IR cloud tracking from VIRTIS/VEX. Dashed green arrows indicate branches of Hadley cells that are not observable in the experiment. (b) Mean latitudinal profiles of the meridional wind from several experiments; line colors correspond with those in (a), line types correspond with the legend. Two vertical lines located at v = 0 axis limit the latitude range of the 1.74 µm cloud tracking profile (green line) where the meridional wind becomes south-poleward.
Source publication
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...
Citations
... For instance, the VEGA balloons that detected northward winds in both hemispheres close to the equator present another example of such an asymmetry, albeit in the middle cloud (52-53 km) [36]. Additionally, in the lower cloud level on the nightside (1.74 μm VIR-TIS-M/ Venus Express), the meridional flow was shown to occasionally change direction around 7 °S [37]. ...
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”.
... The meridional velocities measured in the VIS channel slightly exceed those derived from the near-IR images over the entire latitude range that can be explained by higher levels sounded in the visible range. Gorinov et al. (2021) used VIRTIS/VEX imaging at 1.74 μm to characterize the circulation in the lower cloud (about 48-53 km) on the night side. The meridional motion was found to be mainly equatorward with evidences of poleward motions in equatorial region. ...
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.
... Near the 60 • latitude, in both hemispheres, there are hints of a weak jet, although this cannot confirmed out of the error bars. At higher latitudes, we observed the expected steady decrease towards the poles already reported in previous works [5,21,22,52]. ...
... As already stated, our measurements of the nightside meridional winds display no clear trend at the lower cloud deck, a result in agreement with previous reports from VEx [21] and Akatsuki [22]. Nevertheless, using higher-accuracy wind measurements and the larger data set from VIRTIS-M, Gorinov et al. [52] showed that meridional winds at the nightside lower clouds exhibit abrupt changes in its sign at lower latitudes, a result to be confirmed with our further studies via more accurate measurements. In any case, results of meridional wind velocities from both ground-based observations and space missions (VEx/VIRTIS and Akatsuki/IR2) [21,22,52] seem inconsistent with a Hadley cell circulation at the lower clouds. ...
... Nevertheless, using higher-accuracy wind measurements and the larger data set from VIRTIS-M, Gorinov et al. [52] showed that meridional winds at the nightside lower clouds exhibit abrupt changes in its sign at lower latitudes, a result to be confirmed with our further studies via more accurate measurements. In any case, results of meridional wind velocities from both ground-based observations and space missions (VEx/VIRTIS and Akatsuki/IR2) [21,22,52] seem inconsistent with a Hadley cell circulation at the lower clouds. ...
Characterizing the wind speeds of Venus and their variability at multiple vertical levels is essential for a better understanding of the atmospheric superrotation, constraining the role of large-scale planetary waves in the maintenance of this superrotation, and in studying how the wind field affects clouds’ distribution. Here, we present cloud-tracked wind results of the Venus nightside, obtained with unprecedented quality using ground-based observations during July 2012 with the near-infrared camera and spectrograph (NICS) of the Telescopio Nazionale Galileo (TNG) in La Palma. These observations were performed during 3 consecutive days for periods of 2.5 h starting just before dawn, sensing the nightside lower clouds of Venus close to 48 km of altitude with images taken at continuum K filter at 2.28 μm. Our observations cover a period of time when ESA’s Venus Express was not able to observe these deeper clouds of Venus due to a failure in the infrared channel of its imaging spectrometer, VIRTIS-M, and the dates were chosen to coordinate these ground-based observations with Venus Express’ observations of the dayside cloud tops (at about 70 km) with images at 380 nm acquired with the imaging spectrometer VIRTIS-M. Thanks to the quality and spatial resolution of TNG/NICS images and the use of an accurate technique of template matching to perform cloud tracking, we present the most detailed and complete profile of wind speeds ever performed using ground-based observations of Venus. The vertical shear of the wind was also obtained for the first time, obtained by the combination of ground-based and space-based observations, during the Venus Express mission since the year 2008, when the infrared channel of VIRTIS-M stopped working. Our observations exhibit day-to-day changes in the nightside lower clouds, the probable manifestation of the cloud discontinuity, no relevant variations in the zonal winds, and an accurate characterization of their decay towards the poles, along with the meridional circulation. Finally, we also present the latitudinal profiles of zonal winds, meridional winds, and vertical shear of the zonal wind between the upper clouds’ top and lower clouds, confirming previous findings by Venus Express.
... The initial condition is a temperature field with low static stability layers that is gradient wind balanced with the idealized initial super-rotation. It should be noted that the general circulation obtained in AFES-Venus in a quasi-equilibrium state is consistent with previous observations, e.g., [27,28] in many aspects: The zonally averaged zonal wind has a weak mid-latitude jet and almost constant velocity of about 120 m/s in latitudes between 45 • S and 45 • N at the cloud top-level [29], structures of cold collar [30], thermal tide [31,32], planetary-scale streak [33], and small-scale gravity waves [34]. From 1 January, 5th year, data assimilation is performed for one Earth month. ...
... It should be noted that zonally averaged zonal wind and temperature are produced by not only waves but the mean meridional circulation mainly generated by solar heating. Because the diurnal component of solar heating (and thus the thermal tide) is excluded in the present study in order to focus on the Kelvin wave, there are substantial mid-latitude jets (~125 m/s) in both present experiments when compared to real-world observations, e.g., [27,28]. Figure 7 shows latitude-altitude cross-sections of zonally averaged zonal wind (color) and temperature (contour). ...
... It should be noted that zonally averaged zonal wind and temperature are produced by not only waves but the mean meridional circulation mainly generated by solar heating. Because the diurnal component of solar heating (and thus the thermal tide) is excluded in the present study in order to focus on the Kelvin wave, there are substantial mid-latitude jets (~125 m/s) in both present experiments when compared to real-world observations, e.g., [27,28]. ...
At the cloud top of the Venus atmosphere, equatorial Kelvin waves have been observed and are considered to play an important role in the super-rotation. We were able to reproduce the wave in a general circulation model (GCM) by conducting an observing system simulation experiment (OSSE) with the help of a data assimilation system. The synthetic horizontal winds of the Kelvin wave produced by the linear wave propagating model are assimilated at the cloud top (~70 km) in realistic conditions, assuming they are obtained from cloud tracking of ultra-violet images (UVI) taken by the Venus orbiters. It is demonstrated using Eliassen–Palm (EP) fluxes that the reproduced Kelvin wave transports angular momentum and plays an important role in the magnitude and structure of the super-rotation, causing the acceleration and deceleration of zonal wind of ~0.1 m/s day−1. The conditions required in order to reproduce the Kelvin wave have also been investigated. It is desirable to have 24 hourly dayside satellite observations in an equatorial orbit, such as the Akatsuki Venus climate orbiter. The results of this type of data assimilation study will be useful in the planning of future observation missions to the atmospheres of planets.
... In averaged longwave infrared images faint thermal features were associated with various topographic rises in the equatorial region (Fukuya et al. 2019). Irregular behavior of oxygen nightglow in the upper mesosphere (both in emission intensity and in circulation patterns) was suggestively attributed to highlands in the southern hemisphere, such as Phoebe Regio (Gorinov et al. 2021). ...
... Previously published work from a range of scientific disciplines suggested recent and possibly ongoing volcanic and tectonic activity on Venus (and Idunn Mons in particular), such as spectroscopy (Smrekar et al. 2010;D'Incecco et al. 2017;Cutler et al. 2020;Filiberto et al. 2020Filiberto et al. , 2021a, radar observations (Brossier et al. 2020), andgeology (D'Incecco et al. 2020), with some anomalies also being shown by the wind circulation in the lower atmosphere of Venus, as shown by the VIRTIS-M infrared images (Gorinov et al. 2021). We also showed a new simplified high-resolution geological map of Idunn Mons and atmospheric data on the wind circulation in the lower cloud of Venus (Gorinov et al. 2021). ...
... Previously published work from a range of scientific disciplines suggested recent and possibly ongoing volcanic and tectonic activity on Venus (and Idunn Mons in particular), such as spectroscopy (Smrekar et al. 2010;D'Incecco et al. 2017;Cutler et al. 2020;Filiberto et al. 2020Filiberto et al. , 2021a, radar observations (Brossier et al. 2020), andgeology (D'Incecco et al. 2020), with some anomalies also being shown by the wind circulation in the lower atmosphere of Venus, as shown by the VIRTIS-M infrared images (Gorinov et al. 2021). We also showed a new simplified high-resolution geological map of Idunn Mons and atmospheric data on the wind circulation in the lower cloud of Venus (Gorinov et al. 2021). However, all these works and results analyzed each aspect of active volcanism, tectonism, and atmospheric circulation at Imdr Regio from a very specific and usually single perspective. ...
In 2010 the ESA Venus Express Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument first
observed 1 μm emissivity anomalies over the top and eastern flank of Idunn Mons (46° S; 146° W), a 200 km wide
volcano located in Imdr Regio, a volcano-dominated large volcanic rise of Venus. The anomalies suggest the
presence of chemically unweathered and fresh volcanic deposits, which provided the first hint that volcanism in
this area may have been active during the past few million years. Subsequent studies have investigated the geologic
and atmospheric evolution at Idunn Mons, but no study has comprehensively investigated the evolution and the
implication for recent activity in Idunn Mons. Previous work, using both VIRTIS data and Magellan radar
emissivity data, confirmed the occurrence of unaltered basaltic lava flows at Idunn Mons. Building on that previous
work, experimental laboratory studies have revealed that chemical weathering on Venus may act much faster than
previously expected, which suggests very young ages for these flows. This inference has been supported by
investigations of the tectonic fracturing surrounding Idunn Mons. Finally, atmospheric data from VIRTIS also
show regional anomalies in the speed of the winds in the lower atmosphere over Imdr Regio, which may be related
to very recent or ongoing volcanism. In this paper, we take a comprehensive approach, using atmospheric to
surface measurements, including recent laboratory experiments, to constrain the evolution of Idunn Mons. Our
work suggests that Idunn Mons may be geologically both volcanically and tectonically active today.
A review of the studies on planetary atmospheres performed by Russian scientists in 2019–2022 prepared in the Commission on planetary atmospheres of the National Geophysical Committee for the National Report on Meteorology and Atmospheric Science to the 28 General Assembly of the International Union of Geodesy and Geophysics in Berlin, July 11–20, 2023, is presented.
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.
A number of new Venus mission concepts are being currently evaluated for final approval, such as the NASA VERITAS and DAVINCI+, the Roscosmos-NASA Venera-D and the ESA EnVision proposals. These missions would analyze different aspects of the Earth’s twin planet: the chemistry and structure of its atmosphere, the spectral characteristics and composition of its surface, and its gravity anomalies. The wealth of high-resolution data to be produced by these future missions would likely shed new light on the major science questions. In this regard, one of the major debates concerns whether Venus underwent (and it is currently undergoing) through several episodes of abrupt and catastrophic resurfacing which rejuvenated its entire surface in a short amount of time, or its volcanism has been more steady and constant in time. Recent studies of Imdr Regio, one of the young volcanic rises, have provided hints indicating that volcanic as well as tectonic activity may be still ongoing in that area. The young volcanic rises are generated and supported by underlying active mantle plumes and can be considered as the some of the youngest geologic terrains of Venus. Studying how the rate and styles of volcanic and tectonic activities are evolving through time will tell us more about the interior structure of Venus, shedding some light on the major debate between catastrophic and equilibrium resurfacings. For this reason, we propose here the young volcanic rises, and in particular Idunn Mons of Imdr Regio, as potential target sites for future orbital and in-situ investigations.
