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O. I. Korablev
variations and periodicities. In low latitudes the mean zonal wind at cloud tops
(67 ± 2 km) is about 90 m/s with a maximum of about 100 m/s at 40–50°S.
Poleward of 50°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°S [Khatuntsev et al., 2013].
Fig. 3 Latitudinal profi les of zonal wind (a) and corresponding rotation periods (b)
determined by cloud tracking for several individual orbits
[Khatuntsev et al., 2013]
The dynamics of Venus’ mesosphere (60–100 km altitude) was investigated
using data acquired by the radio-occultation experiment VeRa on board Venus
Express. VeRa provides vertical profi les of density, temperature and pressure
between 40 and 90 km of altitude with a vertical resolution of few hundred me-
ters of both the Northern and Southern hemisphere. Pressure and temperature
vertical profi les were used to derive zonal winds, the cyclostrophic balance,
which applies well on slowly rotating planets with fast zonal winds, like Venus
and Titan. The main features of the retrieved winds are a midlatitude jet with a
maximum speed up to 140 ± 15 m s
‑1
which extends between 20°S and 50°S
latitude at 70 km altitude and a decrease of wind speed with increasing height
above the jet. Cyclostrophic winds show satisfactory agreement with the cloud-
tracked winds derived from the VMC/ Venus Express UV images, although a
disagreement is observed at the equator and near the pole due to the breakdown
of the cyclostrophic approximation [Piccailli et al., 2012].
The average fi elds of the Venus atmosphere are derived from the nighttime
observations in the 1960–2350 cm
‑1
spectral range by VIRTIS-M/Venus Express.
These fi elds include: (a) the air temperatures in the 1–100 mbar pressure range
(~85–65 km above the surface), (b) the altitude of the clouds top, and (c) the
average CO mixing ratio. At the lowest altitudes probed by VIRTIS (~65 km),
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Planetary Atmospheres
air temperatures are strongly asymmetric around midnight, with a pronounced
minima at 3LT, 70°S. Moving to higher levels, the air temperatures first become
more uniform in local time (~75 km), then display a colder region on the evening
side at the upper boundary of VIRTIS sensitivity range (~80 km). The cloud
effective altitude increases monotonically from the South Pole to the equator.
However, the variations observed in night data are consistent with an overall
variation of just 1 km, much smaller than the 4 km reported for the dayside. The
cloud altitudes appear slightly higher on the evening side. Both observations are
consistent with a less vigorous meridional circulation on the nightside of the
planet. Carbon monoxide is not strongly constrained by the VIRTIS-M data.
However, average fields present a clear maximum of 80 ppm around 60°S, well
above the retrieval uncertainty [Grassi et al., 2014].
The mechanisms of the global circulation in the atmosphere of Venus have
been studied with the use of numerical models. To calculate the heating/cooling
of the atmosphere due to absorption/emission of electromagnetic radiation under
initially weak and strong superrotation of the atmosphere, the complete system
of gas dynamics equations in the relaxation approximation was considered. Heat‑
ing parameters, at which the modeled zonal superrotation velocity turned out to
be close to the observed one, have been found. High mountains on Venus induce
a substantial increase of the vertical component of the wind speed and noticeably
influence the global distribution of the horizontal wind at above 80 km, while its
effect below 60 km is weak. [Mingalev et al., 2012, 2015].
Large-scale and small scale turbulence in the atmosphere of Venus is studied
theoretically and using the experimental data including those acquired with the
Venus Express spacecraft. The atmospheres of the Earth and Venus are com‑
pared, allowing to conclude that there is a inverse spectral flux of energy in the
atmosphere of Venus, as in the terrestrial atmosphere, which participates in gen‑
erating the superrotation of the atmosphere [Izakov, 2012, 2013].
4. Outer Planets and Their Satellites
Far ultraviolet spectral observations have been made with the Hubble Space
Telescope in the time-tag mode with the Space Telescope Imaging Spectrograph
(STIS) long slit allowing to build up the first spectral maps of the FUV Jovian
aurora. The results are confirmed with modeling [Gerard et al., 2014].
Observational data on hydrocarbons, nitriles, and ions on Titan are compared
with predictions of the photochemical model. Uncertainties of the observed
abundances and differences between the data from different instruments and
observing teams are comparable with the differences between the observations
and the model results. Formation of haze by polymerization of hydrocarbons and
nitriles and recombination of heavy ions is calculated along with condensation
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O. I. Korablev
of various species near the tropopause. Overall deposition forms a layer of
300 m thick for the age of the Solar System, and nitrogen constitutes 8% of the
deposition. The model reproduces the basic observational data and adequately
describes basic chemical processes in Titan’s atmosphere and ionosphere [Kras‑
nopolsky 2014]
5. Comparative studies of the atmospheres of planets
and their satellites
5.1. Planetary boundary layer
Different aspects of planetary boundary layer described in the shallow-water
approximation are studied in the frame of a finite-volume numerical method
[Karelsky et al., 2012, 2013; Karelsky, Petrosyan, 2013; Chernyak et al., 2013].
A model for the density of vertical mass flux of dust in the convective atmos‑
pheric boundary layer as a function of the density of convective elements, in‑
cluding vortices, friction velocity, and vertical buoyancy is proposed. Two meth‑
ods for experimentally determining the density of convecting elements are
discussed, optical, as observations by Mars Exploration Rover (MER) camera in
Gusev carter on Mars [Kurgansky 2012], and using a muber of detecting stations
placed perpendicular to the dominating wind vector. The results are validated
using field observations [Kurgansky 2014].
Observations of fine mineral dust aerosol (0.15–15 μm) were carried out in
Kalmykia in 2007, 2009, and 2010 under conditions of weak wind and strong
heating of the surface, in the absence of saltation processes. These results show
that the fine mineral dust aerosol (0.15–0.5 μm) contributes considerably to the
total aerosol content. The problem of stationary convective flows over a nonuni‑
formly heated wavy surface is studied in the context of a simplified analytical
model. It is shown that the horizontally periodic heating of such a surface can
lead to a “thermal wind” effect, i. e., the generation of a uniform horizontal flow
far from the surface. Estimations for Mars conditiona are suggested [Chkhetiani
et al., 2012, 2013].
A review on the boundary layer of mars is published [Petrosyan et al., 2011].
5.2. Outer Atmospheres and Escape
The processes of kinetics and transport of hot oxygen and hydrogen atoms in
the transition (from the thermosphere to the exosphere) region of the upper Mar‑
tian atmosphere are studied. It is shown that the exosphere is populated with a
significant number of suprathermal oxygen atoms with kinetic energies ranging
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