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1.
Data on the thermal structure of the nightside middle atmosphere of Venus, from 84 to 137 km altitude, have been obtained from analysis of deceleration measurements from the third Pioneer Venus small probe, the night probe, which entered the atmosphere near the midnight meridian at 27°S latitude. Comparison of the midnight sounding with the morning sounding at 31°S latitude indicates that the temperature structure is essentially diurnally invariant up to 100 km, above which the nightside structure diverges sharply from the dayside toward lower temperatures. Very large diurnal pressure differences develop above 100 km with dayside pressure ten times that on the nightside at 126 km altitude. This has major implications for upper atmospheric dynamics. The data are compared with the measurements of G. M. Keating, J. Y. Nicholson, and L. R. Lake (1980, J. Geophys. Res., 85, 7941–7956) above 140 km with theoretical thermal structure models of Dickinson, and with data obtained by Russian Venera spacecraft below 100 km. Midnight temperatures are ～ 130°K, somewhat warmer than those reported by Keating et al. 相似文献
2.
The interpretation of unexpected characteristics of Pioneer Venus temperature measurements, and of the large difference between these and the Venera results, is aided by new Venus temperature profiles derived from engineering measurements of the Pioneer Venus Small-Probe Net Flux Radiometer (SNFR) instruments. To facilitate correction of a temperature-dependent radiometric response, these instruments monitored the temperatures of their deployed radiation detectors. The accurate calibration of the temperature sensors, and their strong thermal coupling to the atmosphere, make it possible to deduce atmospheric temperatures within 2°K (at most altitudes) using a simple two-component thermal model to account for lag effects. These independent temperature profiles generally confirm to high accuracy, the small-probe results of A. Seiff, D. B. Kirk, R. E. Young, R. C. Blanchard, J. T. Findlay, G. M. Kelly, and S. C. Sommer (1980a, J. Geophys. Res.85, pp. 7903–7933) concerning vertical structure and horizontal contrast in the lower atmosphere, although the stable layer below 25 km is found to be slightly more stable (by about 0.4°K/km) and absolute temperatures are an average of 2°K higher. The measured Day-Night thermal contrast is compatible with predicted responses to the diurnal variation in solar heating, except near the cloud base, where 3–5°K differences may be due to thermal radiative heating differences associated with different cloud opacities. Temperature contrasts between latitudes 30 and 60° are roughly consistent with cyclostrophic balance. But pressure and temperature measurements by the Pioneer Venus Sounder probe at 4° latitude, when compared to Small-probe results, imply unreasonably large equatorward accelerations of 100 (m/sec)/day. Poleward accelerations compatible with cyclostrophic balance can be obtained if Sounder-probe temperatures are increased by a scale-factor correction reaching 6–7°K at 13 km. 相似文献
3.
M.Ya. Marov 《Icarus》1972
In situ measurements of the Venus atmosphere, made by the entry probes Venera 4, 5, 6, and 7, and data from the Mariner 5 flyby, have provided essentially new and reliable information and have powerfully contributed to our understanding of the nearest planet. The abundances of the principal atmospheric constituents and the temperature and pressure profiles down to the Venus surface were obtained for the first time. It was shown that the atmosphere is composed primarily of CO2 and that N2 (if any) and H2O are relatively minor admixtures. In the region of the Venera 7 landing, the temperature and pressure at the Venus surface were established as equal to 747 ± 20°K and 90 ± 15 kgcm−2. Space vehicles have also provided limited but quite important information on the physical properties of the Venus upper atmosphere and ionosphere, and on the interaction of the planet with the interplanetary environment. The main characteristics of the Venus atmosphere are discussed here with emphasis on the Venera results, including instrumentation, data processing, and altitude profiles. 相似文献
4.
Microwave spectra of carbon monoxide (12CO) in the mesosphere of Venus were measured in December 1978, May and December 1980, and January, September, and November 1982. These spectra are analyzed to provide mixing profiles of CO in the Venus mesosphere and best constrain the mixing profile of CO between ～ 100 and 80 km altitude. From the January 1982 measurement (which, of all our spectra, best constrains the abundance of CO below 80 km altitude) we find an upper limit for the CO mixing ratio below 80 km altitude that is two to three times smaller than the stratospheric (～65 km) value of 4.5 ± 1.0 × 10?5 determined by P. Connes, J. Connes, L.D. Kaplan, and W. S. Benedict (1968, Astrophys. J.152, 731–743) in 1967, indicating a possible long-term change in the lower atmospheric concentration of CO. Intercomparison among the individual CO profiles derived from our spectra indicates considerable short-term temporal and/or spatial variation in the profile of CO mixing in the Venus mesosphere above 80 km. A more complete comparison with previously published CO microwave spectra from a number of authors specifies the basic diurnal nature of mesospheric CO variability. CO abundance above ～ 95 km in the Venus atmosphere shows approximately a factor of 2–4 enhancement on the nightside relative to the dayside of Venus. Peak nightside CO abundance above ～95 km occurs very near to the antisolar point on Venus (local time of peak CO abundance above ～95 km occurs at 0.6?0.6+0.7 hr after midnight on Venus), strongly suggesting that retrograde zonal flow is substantially reduced at an altitude of 100 km in the Venus mesosphere. In contrast, CO abundances between 80 and 90 km altitude show a maximum that is shifted from the antisolar point toward the morningside of Venus (local time of peak CO abundance between 80 and 90 km occurs at 8.5 ± 1.0 hr past midnight on Venus). The magnitude of the diurnal variation of CO abundance between 80 and 90 km is again, approximately a factor of 2–4. Disk-averaged spectra of Venus do not determine the exact form for the diurnal distribution of CO in the Venus mesosphere as indicated by comparison of synthetic spectra, based upon model distributions, and the measured spectra. However, the offset in phase for the diurnal variation for the >95 km and 80–90-km-altitude regions requires an asymmetric (in solar zenith angle) distribution. 相似文献
5.
Radio emissions attributed to lightning on Venus have been recorded by Venera 11 and 12 and by the Pioneer Venus Orbiter. The Venera descent records are compared to patterns of radio propagation within the Venusian atmosphere and an explanation is found for some timing trends that, if correct, indicates the lightning was below 33 km in altitude. 相似文献
6.
Two extreme ultraviolet (EUV) spectrophotometers flown in December 1978 on Venera 11 and Venera 12 measured the hydrogen Lyman α emission resonantly scattered in the atmosphere of Venus. Measurements were obtained across the dayside of the disk, and in the exosphere up to 50,000 km. They were analyzed with spherically symmetric models for which the radiative transfer equation was solved. The H content of the Venus atmosphere varies from optically thin to moderately thick regions. A shape fit at the bright limb allows one to determine the exospheric temperature Tc and the number density nc independently of the calibration of the instrument or the exact value of the solar flux. The dayside exospheric temperature was measured for the first time in the polar regions, with Tc = 300 ± 25°K for Venera 11 (79°S) and Tc = 275 ± 25°K (59°S) for Venera 12. At the same place, the density is nc = 4?2+3 × 104 atom.cm?3, and the integrated number density Nt from 250 to 110 km (the level of CO2 absorption) is 2.1 × 1012 atom.cm?2, a factor of 3 to 6 lower than that predicted in aeronomical models. This probably indicates that the models should be revised in the content of H-bearing molecules and should include the effect of dynamics. Across the disk the value of Nt decreases smoothly with a total variation of two from the morning side to the afternoon side. Alternately it could be a latitude effect, with less hydrogen in the polar regions. The nonthermal component if clearly seen up to 40,000 km of altitude. It is twice as abundant as at the time of Mariner 10 (solar minimum). Its radial distribution above 4000 km can be simulated by an exospheric distribution with T = 1030K and n = 103 atom.cm?3 at the exobase level. However, there are less hot atoms between 2000 and 4000 km than predicted by an ionospheric source. A by-product of the analysis is a determination of a very high solar Lyman α flux of 7.6 × 1011 photons (cm2 sec Å)?1 at line center (1 AU) in December 1978. 相似文献
7.
Submillimeter line observations of CO in the Venus middle atmosphere (mesosphere) were observed with the James Clerk Maxwell Telescope (JCMT, Mauna Kea) about the May 2000, February 2002 superior and July 1999, March 2001 inferior conjunctions of Venus. Combined 12CO and 13CO isotope spectral line measurements at 345 and 330 gHz frequencies, respectively, provided enhanced sensitivity and vertical coverage for simultaneous retrievals of atmospheric temperatures and CO mixing ratios over the altitude region 75-105 km with vertical resolution 4-5 km. Supporting millimeter 12CO spectral line observations with the Kitt Peak 12-m telescope (Steward Observatories) provide enhanced temporal coverage and CO mixing sensitivity. Implementation of CO/temperature profile retrievals for the 2000, 2002 dayside (superior conjunction) and 1999, 2001 nightside (inferior conjunction) periods yields a first-time definition of the vertical structure and diurnal variation of a low-to-mid-latitude mesopause within the Venus atmosphere. At the times of these 1999-2002 observations, the Venus mesopause was located at a slightly lower level in the nightside (0.5 mbar, ∼87 km) versus the dayside (0.2 mbar, ∼91 km) atmosphere. Average diurnal variation of Venus mesospheric temperatures appears to be ≤ 5 K at and below the mesopause. Diurnal variation of Venus thermospheric temperatures increases abruptly just above the mesopause, reaching 50 K by the 0.01-mbar pressure level (∼102 km). Atmospheric temperatures above and below the Venus mesopause exhibited global-scale (≥4000 km horizontal) variations of large amplitude (7-15 K) on surprisingly short timescales (daily to monthly) during the 2001 nightside and 2002 dayside observing periods. Venus dayside mesospheric temperatures observed during the 2002 superior conjunction were also 10-15 K warmer than observed during the 2000 superior conjunction. A characteristic timescale for these global temperature variations is not defined, but their magnitude is comparable to previous determinations of secular variability in nightside mesospheric temperatures (Clancy and Muhleman, 1991). 相似文献
8.
Observations of Venus using the ultraviolet filter of the Venus Monitoring Camera (VMC) on ESA’s Venus Express Spacecraft (VEX) provide the best opportunity for study of the spatial and temporal distribution of the venusian unknown ultraviolet absorber since the Pioneer Venus (PV) mission. We compare the results of two sets of 125 radiative transfer models of the upper atmosphere of Venus to each pixel in a subset of VMC UV channel images. We use a quantitative best fit criterion based upon the notion that the distribution of the unknown absorber should be independent of the illumination and observing geometry. We use the product of the cosines of the incidence and emission angles and search for absorber distributions that are uncorrelated with this geometric parameter, finding that two models can describe the vertical distribution of the unknown absorber. One model is a well-mixed vertical profile above a pressure level of roughly 120 mb (～63 km). This is consistent with the altitude of photochemical formation of sulfuric acid. The second model describes it as a thin layer of pure UV absorber at a pressure level roughly around 24 mb (～71 km) and this altitude is consistent with the top of upper cloud deck. We find that the average abundance of unknown absorber in the equatorial region is 0.21 ± 0.04 optical depth and it decreases in the polar region to 0.08 ± 0.05 optical depth at 365 nm. 相似文献
9.
Using a quasi-two-dimensional model of the Venus ionosphere, we calculated the ion number densities and horizontal ion bulk velocities expected for a range of solar zenith angles near the terminator (80 to 100°), and compared them with data obtained from the Pioneer Venus Orbiter retarding potential analyzer. The calculated ion bulk velocity arises entirely from the solar EUV-induced plasma pressure gradient and has a magnitude consistent with observations; ionization by suprathermal electrons is neglected in those computations. We find that while photoionization is the dominant source of ionospheric plasma for solar zenith angles less than 92°, plasma transport from the dayside is the dominant plasma source for solar zenith angles greater than 95°. We also show that the main nightside plasma peak at approximately 140 km altitude is of the F2 type (i.e., is diffusion controlled). Its altitude and shape are thus quite insensitive to the altitude of the ion source. 相似文献
10.
Basil Petropoulos 《Earth, Moon, and Planets》1988,42(1):29-40
The following parameters have been computed for the Cytherean atmosphere: pressure, density, speed of sound, collisional frequency, column mass, density scale, mean-free-path, viscosity, pressure scale, mean particle velocity, number density at an altitude from 0 to 170 km.The chemical composition, the temperature distribution function of the altitude, the surface pressure and the surface temperature measured by Pioneer Venus have been used as input data for these computations. 相似文献
11.
A. Piccialli S. Tellmann D.V. Titov S.S. Limaye I.V. Khatuntsev M. Pätzold B. Häusler 《Icarus》2012,217(2):669-681
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 profiles of density, temperature and pressure between 40 and 90 km of altitude with a vertical resolution of few hundred meters of both the Northern and Southern hemisphere. Pressure and temperature vertical profiles were used to derive zonal winds by applying an approximation of the Navier–Stokes equation, 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 Venus Monitoring Camera (VMC/VEx) UV images, although a disagreement is observed at the equator and near the pole due to the breakdown of the cyclostrophic approximation. Knowledge of both temperature and wind fields allowed us to study the stability of the atmosphere with respect to convection and turbulence. The Richardson number Ri was evaluated from zonal field of measured temperatures and thermal winds. The atmosphere is characterised by a low value of Richardson number from ～45 km up to ～60 km altitude at all latitudes that corresponds to the lower and middle cloud layer indicating an almost adiabatic atmosphere. A high value of Richardson number was found in the region of the midlatitude jet indicating a highly stable atmosphere. The necessary condition for barotropic instability was verified: it is satisfied on the poleward side of the midlatitude jet, indicating the possible presence of wave instability. 相似文献
12.
The following physical parameters have been computed for the atmosphere of Venus between 65 and 90 km, by intervals of 1 km. (1) Pressure, (2) Density, (3) Speed of sound, (4) Number density, (5) Density scale, (6) Pressure scale, (7) Collisional frequency, (8) Mean particle velocity (9) Mean free path, (10) Columnar mass, (11) Viscosity. For these calculations we have used the temperature altitude measurements of Venera 15 and 16 at 52 °N and 72 °N latitudes, the night and 70 °N and 72 °N latitudes the day. 相似文献
13.
M.V. Keldysh 《Icarus》1977,30(4):605-625
In October 1975 the Venera 9 and 10 space vehicles reached Venus. Two landers separated from the spacecraft and soft-landed on the illuminated side of the planet while their remaining orbiters were inserted into highly elliptical orbits, with pericenters at about 7600 km. These flights became a very important step in the Soviet program of Venus exploration. For the first time two panoramas of the Venus surface were returned to the Earth. Both landers and orbiters were equipped with various scientific instruments for studying the structure and dynamics of the atmosphere, physical properties and structure of the clouds, light attenuation in the atmosphere and illumination properties of the surface at the landing sites, and the composition, structure, and interaction processes in the Venus upper atmosphere and environment. The experiments were of complex character due to the simultaneous measurements from landers and orbiters, while the orbiters delivered very important information provided by systematic observations of the planet with great time and space coverage. In this report the principal characteristics of the flights, construction of the spacecraft, instrumentation, and scheme of landing on the surface are described. The preliminary results of the measurements obtained and their tentative interpretation are discussed. 相似文献
14.
Two coherently related radio signals transmitted from Voyager 1 at wavelengths of 13 cm (S-band) and 3.6 cm (X-band) were used to probe the equatorial atmosphere of Titan. The measurements were conducted during the occultation of the spacecraft by the satellite on November 12, 1980. An analysis of the differential dispersive frequency measurements did not reveal any ionization layers in the upper atmosphere of Titan. The resolution was approximately 3 × 103 and 5 × 103 electrons/cm3 near the evening and morning terminators, respectively. Abrupt signal changes observed at ingress and egress indicated a surface radius of 2575.0 ± 0.5 km, leading to a mean density of 1.881 ± 0.002 g cm?3 for the satellite. The nondispersive data were used to derive profiles in height of the gas refractivity and microwave absorption in Titan's troposphere and stratosphere. No absorption was detected; the resolution was about 0.01 dB/km at the 13-cm wavelength. The gas refractivity data, which extend from the surface to about 200 km altitude, were interpreted in two different ways. In the first, it is assumed that N2 makes up essentially all of the atmosphere, but with very small amounts of CH4 and other hydrocarbons also present. This approach yielded a temperature and pressure at the surface of 94.0 ± 0.7°K and 1496 ± 20 mbar, respectively. The tropopause, which was detected near 42 km altitude, had a temperature of 71.4 ± 0.5°K and a pressure of about 130 mbar. Above the tropopause, the temperature increased with height, reaching 170 ± 15°K near the 200-km level. The maximum temperature lapse rate observed near the surface (1.38 ± 0.10°K/km) corresponds to the adiabatic value expected for a dry N2 atmosphere—indicating that methane saturation did not occur in tbis region. Above the 3.5-km altitude level the lapse rate dropped abruptly to 0.9 ± 0.1°K/km and then decreased slowly with increasing altitude, crossing zero at the tropopause. For the N2 atmospheric model, the lapse rate transition at the 3.5-km level appears to mark the boundary between a convective region near the surface having the dry adiabatic lapse rate, and a higher stable region in radiative equilibrium. In the second interpretation of the refractivity data, it is assumed, instead, that the 3.5 km altitude level corresponds to the bottom of a CH4 cloud layer, and that N2 and CH4 are perfectly mixed below this level. These assumptions lead to an atmospheric model which below the clouds contains about 10% CH4 by number density. The temperature near the surface is about 95°K. Arguments concerning the temperature lapse rates computed from the radio measurements appear to favor models in which methane forms at most a limited haze layer high in the troposphere. 相似文献
15.
Eighty-seven measurements of the thermal structure in the atmosphere of Venus between the altitudes of about 40 and 85 km were derived from Pioneer Venus Orbiter radio occultation data taken during four occultation seasons from December 1978 to October 1981. These measurements cover latitudes from ?68 to 88° and solar zenith angles of 8 to 166°. The results indicate that the characteristics of the thermal structure in both the troposphere and stratosphere regions are dependent predominantly on the latitude and only weakly on solar illumination conditions. In particular, the circumpolar collar cloud region in the northern hemisphere (latitude 55 to 77°) displays the most dramatic changes in structure, including the appearance of a large inversion, having an average magnitude of about 18°K and a maximum of about 33°K. Also in this region, the tropopause altitude rises by about 4.8 km above its value at low latitudes, the tropopause temperature drops by about 60°K, and the pressure at the tropopause decreases by an average of about 240 mbar. These changes in the collar region are correlated with observations of increased turbulence and greater amplitude of thermal waves in the region, which is located where the persistent circulation pattern in the Venus atmosphere changes from zonally symmetric retrograde rotation to a hemispherical circumpolar vortex. It was shown that the large zonal winds associated with this circulation pattern are not likely to produce distortions in the atmosphere of a magnitude that could lead to temperature errors of the order of the mesosphere inversions observed in the collar region, but under certain circumstances zonal wind distortion could cause errors of 3–4°K. 相似文献
16.
The altitude variation of the zonal wind velocity in the Venus atmosphere above the cloud layer is deduced from the structure of the wavenumber 2 solar tide. Results show that the amplitude of the zonal wind increases with respect to altitude near the equator, but decreases for latitudes greater than 30°. Thus, the zonal wind becomes concentrated at lower latitudes by 100 km altitude. 相似文献
17.
High vertical resolution scans of the Venus limb made by the Pioneer Venus Orbiter Cloud Photopolarimeter at 365 nm and 690 nm wavelengths are used to investigate the level of the haze top, and haze particle properties and scale height. Haze particle vertical optical depth 0.01 occurs at altitude 80 to 85 km based on knowledge of instrument pointing. The lowest haze tops were observed close to subsolar longitudes but the data set supports a longitude dependence no more than a temporal variation. Single scattering computations for a spherical shell atmosphere show good agreement with observed intensities for particles smaller than 0.3 μm radius and refractive index less than 1.7, consistent with, but not limited to, concentrated sulfuric acid. Particle scale height in the 0.5 to 2 mbar pressure regions varies between 1 and 3 km over the season (12 of 92 days), latitude (15–45°N), and local time (0900–1800) ranges of the observations. Detached layers of haze are sometimes present. An average particle scale height of 2.2 km at 84 km altitude yields an eddy diffusion coefficient of 1.3 × 105 cm2 sec?1. 相似文献
18.
Between November 23 and 28, 2007, the Cologne Tuneable Heterodyne Infrared Spectrometer THIS was installed at the McMath-Pierce Solar Telescope (Kitt Peak, Arizona, USA) to determine zonal wind velocities and to estimate the subsolar-to-antisolar flow. We investigate dynamics in the upper atmosphere of Venus by measuring the Doppler shift of fully-resolved non-LTE CO2 emission lines at 959.3917 cm?1 (10.423 μm), which probe a narrow altitude region in Venus’ atmosphere around 110 ± 10 km (～1 μbar). The results show no significant zonal wind velocity at the equator. An increase with latitude up to 43 ± 13 m/s at a latitude of 33°N was observed. This confirms the deduction of a minor influence of Venus superrotation at an altitude of 110 km from previous measurements in May 2007 (Sornig et al., 2008). The specific observing geometry enables estimating the maximum cross terminator velocity of the subsolar-to-antisolar flow at 72 ± 47 m/s. 相似文献
19.
We have computed the physical parameters for the Venus atmosphere between 0–64 km altitude by using Vega measurements. The proposed model can be used in order to study the structure of Venus atmosphere and its chemical comoposition between 60–64 km, where an inversion in temperature profiles has been measured by Vega. 相似文献
20.
An examination of the effect of assumptions in the interpretation of the Venera wind data is made as a rebuttal to the suggestion by A.T. Young that the 140 m/sec Venera 8 horizontal wind at 45 km may be either spurious or anomalous. The Venera measurements of wind speed along with the Mariner measurements of a lower region of strong turbulence are evidence for a wide band of variable high-speed retrograde horizontal winds which girdle Venus at the equator. In the prevalent interpretation of the Mariner 10 uv photographs, the region of the top of the visible cloud is characterized by variable high-speed retrograde horizontal winds which orbit Venus with an average period of 4 Earth days, and by many features indicating vertical convection. This interpretation, together with the possibility of atmospheric corotation due to frictional coupling, suggests that the Venera-Mariner band of winds at 45 km extends well beyond the top of the visible cloud, and that the upper region of strong turbulence detected by the Mariners may result in part from vertical convection currents carried along by high-speed horizontal winds. In an alternate interpretation of the Mariner 10 uv photographs Young suggests that the predominant motions may be traveling wavelike disturbances with a 4-day period rather than bulk motion of the atmosphere. For this case the upper region of strong turbulence is interpreted as due mostly to vertical wind shear resulting from a rapid decrease in wind speed within a relatively short distance above the Venera-Mariner band of high-speed winds. 相似文献