共查询到20条相似文献，搜索用时 15 毫秒
1.
The interferometer visibility of Jupiter, observed at a wavelength of 3.4 mm, is used to determine the global limb darkening of the planet's brightness. From a single-parameter fit to the visibility curve, we find an ammonia-to-molecular hydrogen mixing ratio of 6.4[+5.1, ?1.9] × 10?5, which corresponds to 35[+28, ?10]% of the solar nitrogen abundance if all of the nitrogen is in the form of ammonia. The fitting procedure uses a simple model atmosphere for the Jovian atmosphere which is based on other observations of the planet. The dependence of the result on the various model parameters is studied. 相似文献
2.
The methane abundance in the lower Jovian stratosphere is measured using Galilean satellite eclipse light curves. Spectrally selective observations in and between absorption bands are compared. An average mixing ratio at the locations measured is [CH4]/[H2] ～ 1.3 × 10?3, larger than the value 0.9 × 10?3 expected for a solar abundance of carbon. Some zenographic variation of the mixing ratio may occur. Observationally compatible values are 1.3–2.0 × 10?3 in the STZ, 1.3– 2.6 × 10?3 on the GRS/STrZ edge, and 0.7–1.3 × 10?3 in the GRS. 相似文献
3.
The u.v. spectrometer polarimeter on the Solar Maximum Mission has been utilized to measure mesospheric ozone vs altitude profiles by the technique of solar occultation. Sunset data are presented for 1980, during the fall equinoctal period within ± 20° of the geographic equator. Mean O3, concentrations are 4.0 × 1010 cm?3at 50 km, 1.6 × 1010 cm?3 at 55 km. 5.5 × 109 cm?3 at 60 km and 1.5 × 109 cm?3 at 65 km. Som profiles exhibit altitude structure which is wavelike. The mean ozone profile is fit best with the results of a time-dependent model if the assumed water vapor mixing ratio employed varies from 6 ppm at 50 km to 2–4 ppm at 65 km. 相似文献
4.
Nonthermal escape processes responsible for the escape of hydrogen and deuterium from Venus are examined for present and past atmospheres. Three mechanisms are important for the escape of hydrogen from the present atmosphere: (a) charge exchange of plasmaspheric H+ with exospheric H, (b) impact of exospheric hot O atoms on H, and (c) ion molecule reactions involving O+ and H2. However, in the past when the H abundance was higher, the charge-exchange mechanism would be the strongest. The H escape flux increases rapidly with increasing hydrogen abundance in the upper atmosphere and saturates at a value of 1 × 1010 cm?2 sec?1 emerging primarily from the day side when the H mixing ratio at the homopause is 2 × 10?3. This corresponds to an H2O mixing ratio of 1 × 10?3 at the cold trap and ～15% at the surface. Deuterium would also escape by the charge-exchange mechanism and a D/H enrichment by a factor of ～1000 over the nonthermal escape regime is expected, which could have lasted over the last 3 billion years. Coincidentally, the onset of hydrodynamic flow leading to efficient H escape occurs just at the H2O mixing ratio at which the charge-exchange escape flux saturates. Thus it is possible that Venus has lost an Earth-equivalent ocean of water over geologic time. If so, either the D/H enrichment has been kept low by modest outgassing of juvenile water or Venus started out with a D/H ratio of ～4.0 × 10?6. 相似文献
5.
V.G. Teifel 《Icarus》1983,53(3):389-398
Modeling of the geometric albedo of Uranus in and near prominent methane absorption bands between 0.5 and 0.9 μm indicates that the visible atmosphere probably consists of a thin aerosol haze layer (τscat ? 0.3?0.5; ωH ? 0.95) above an optically thick, semi-infinite Rayleigh scattering atmosphere. A significant depletion of methane gas above the haze layer is indicated. The mixing ratio of methane in the lower atmosphere is consistent with a value of CH4/H2 ? 3 × 10?3, comparable to those derived for Jupiter and Saturn. 相似文献
6.
Oxidation of CH4 provides the major source for atmospheric H2 which is removed mainly by reaction with OH. Biological activity at the Earth's surface appears to represent at most a minor sink for H2. Anthropogenic activity is a significant source for both H2 and CO in the present atmosphere and may be expected to exert a growing influence in the future. Models are presented which suggest a rise in the mixing ratio of H2 from its present value of 5.6 × 10?7 to about 1.8 × 10?6 by the year 2100. The mixing ratio of CO should grow from 9.7 × 10?8 to 2.3 × 10?7 over the same time period and there should be a rise in CH4 by about a factor of 1.5 associated with anthropogenically induced reductions in tropospheric OH. 相似文献
7.
Results of the scattered solar radiation spectrum measurements made deep in the Venus atmosphere by the Venera 11 and 12 descent probes are presented. The instrument had two channels: spectrometric (to measure downward radiation in the range 0.45 < γ < 1.17 μm) and photometric (four filters and circular angle scanning in an almost vertical plane). Spectra and angular scans were made in the height range from 63 km above the planet surface. The integral flux of solar radiation is 90 ± 12 W m?2 measured on the surface at the subsolar point. The mean value of surface absorbed radiation flux per planetary unit area is 17.5 ± 2.3 W m?2. For Venera 11 and 12 landing sites the atmospheric absorbed radiation flux is ～15 W m?2 for H >; 43 km and ～45 W m?2 for H < 48 km in the range 0.45 to 1.55 μm. At the landing sites of the two probes the investigated portion of the cloud layer has almost the same structure: it consists of three parts with boundaries between them at about 51 and 57 km. The base of clouds is near 48 km above the surface. The optical depth of the cloud layer (below 63 km) in the range 0.5 to 1 μm does not depend on the wavelength and is ～29 and ～38 for the Venera 11 and 12 landing sites, respectively. The single-scattering albedo, ω0, in the clouds is very close to 1 outside the absorption bands. Below 58 km the parameter (1 ? ω0) is <10?3 for 0.49 and 0.7 μm. The parameter (1 ? ω0) obviously increases above 60 km. Below 48 km some aerosol is present. The optical depth here is a strong function of wavelength. It varies from 1.5 to 3 at λ = 0.49 μm and from 0.13 to 0.4 at 1.0 μm. The mean size of particles below the cloud deck is about 0.1 μm. Below 35 km true absorption was found at λ < 0.55 μm with the (1 ? ω0) maximum at H ≈ 15 km. The wavelength and height dependence of the absorption coefficient are compatible with the assumption that sulfur with a mixing ratio ～2 × 10?8 normalized to S2 molecules is the absorber. The upper limits of the mixing ratio for Cl2, Br2, and NO2 are 4 × 10?8, 2 × 10?11, and 4 × 10?10, respectively. The CO2 and H2O bands are confidently identified in the observed spectra. The mean value of the H2O mixing ratio is 3 × 10?5 < FH2O < 10?4 in the undercloud atmosphere. The H2O mixing ratio evidently varies with height. The most probable profile is characterized by a gradual increase from FH2O = 2 × 10?5 near the surface to a 10 to 20 times higher value in the clouds. 相似文献
8.
The abundance of H2O is derived from the 1900- to 2100-cm?1 region of the Voyager 1 IRIS spectra. Scale variations of about a factor of 2 are seen in the water abundance between the North and South Equatorial Belts. Averaged over the full disk, the mixing ratio is , if H2O is uniformly mixed in the atmospheric region having temperatures of 230 to 270°K; this result implies a solar depletion by a factor of 100 in this region. In the belts, the best agreement is obtained for a H2O/H2 mixing ratio of 4.0 × 10?6 in the NEB and 7.2 × 10?6 in the SEB, assuming a constant mixing ratio. 相似文献
9.
Photochemical calculations indicate that in the prebiotic atmosphere of the Earth ammonia would have been irreversibly converted to N2 in less than 40 years if the ammonia surface mixing ratio were ≤ 10?4. However, if a continuous outgassing of ammonia were maintained, radiative equilibrium calculations indicate that a surface mixing ratio of ammonia of 10?5 or greater would provide a sufficient greenhouse effect to keep the surface temperature above freezing. With a 10?4 mixing ratio of ammonia, 60 to 70% of the present day solar luminosity would be adequate to maintain surface temperatures above freezing. A lower limit to the time constant for accumulation of an amount of nitrogen equivalent to the present day value is 10 my if the outgassing were such as to provide a continuous surface mixing ratio of ammonia ≥ 10?5. 相似文献
10.
Yu. V. Pisanko 《Solar System Research》2005,39(5):426-430
The Parker model is modified to describe a rapid temperature increase from the region of temperature minimum to the coronal base and to relate the electron density in the region of the temperature minimum (～0.85×1011 cm?3 according to the modified model) to that at the orbit of the Earth (～7.42 cm?3 according to the model). The coronal temperature reaches its maximum (1.8×106 K) at the Parker critical point; physical processes at this point are left beyond the scope of the model. It is suggested to consider the expanding solar corona as a self-heating system in which heating of the solar corona is related to the transonic regime of its expansion, which is maintained by the high coronal temperature. 相似文献
11.
Richard W. Zurek 《Icarus》1978,35(2):196-208
This paper examines the solar heating of the Martian atmosphere during the 1971 global dust storm observed by Mariner 9. Radiative scattering as well as absorption is included by utilizing the delta-Eddington approximation to the full radiative transfer equation. The necessary optical parameters are generated by a Mie program which uses a size distribution and a complex refractive index inferred from a number of sources, particularly from recent analyces of Mariner 9 UVS and TV observations. Assuming uniform mixing of the dust, the solar heating per unit mass during a Martian global dust storm is remarkably uniform with height for small solar zenith angles. Heating rates may reach 80°K day? for overhead sunlight. Overall, 20% of the direct insolation is absorbed by the dust-laden atmosphere. Even optically thin widespread dust hazes may produce heating rates of several degrees Kelvin per day. 相似文献
12.
We have constructed a model of the physical processes controlling Titan's clouds. Our model produces clouds that qualitatively match the present observational constraints in a wide variety of model atmospheres, including those with low atmospheric pressures (25 mbar) and high atmospheric pressures. We find the following: (1) high atmospheric temperatures (160°K) are important so that there is a large scale height in the first few optical depths of cloud; (2) the aerosol mass production occurs at very low aerosol optical depth so that the cloud particles do not directly affect the photochemistry producing them; (3) the production rate of aerosol mass by chemical processes is probably greater than 3.5 × 10?14 g cm?2 sec?1; (4) and the eddy diffusion coefficient is less than 5 × 106 cm2 sec?1 except perhaps in the top optical depth of the cloud. Our model is not extremely sensitive to particle shape, but it is sensitive to particle density. Higher particle densities require larger aerosol mass production rates to produce satisfactory clouds. Particle densities of unity require a mass production rate on the order of 3.5 × 10?13 g cm?2 sec?1. We also show that an increase in mass input causes a decrease in the mean particle size, as required by J. B. Pollack et al. (1980, Geophys. Res. Lett. 7, 829–832), to explain the observed correlation between the solar cycle and Titan's albedo; that coagulation need not be extremely inefficient in order to obtain realistic clouds as proposed by M. Podolak and E. Podolak (1980, Icarus43, 73–83); that coagulation could be inefficient due to photoelectric charging of the particles; and, that the lifetime of particles near the altitude of unit optical depth is a few months, as required to explain the temporal variability observed by S. T. Suess and G. W. Lockwood and D. P. Cruikshank and J. S. Morgan (1979, Bull. Amer. Astron. Soc.11, 564). Although Titan's aerosols are ottically thick in the vertical direction, the atmosphere is so extended that the horizontal visibility is greater than that found anywhere at Earth's surface. 相似文献
13.
The scattering and absorption properties of Axel dust were investigated by means of Mie theory. We find that a flat distribution of particle radii between 0 and 0.1 μm, and an imaginary part of the index of refraction which varies as λ?2.5 produce a good fit to the variation of Titan's geometric albedo with wavelength (λ) provided that τext, the extinction optical depth of Titan's atmosphere at 5000 Å, is about 10. The real part of the complex index is taken to be 2.0. The model assumes that the mixing ratio of Axel dust to gas is uniform above the surface of Titan. The same set of physical properties for Axel dust also produces a good fit to Saturn's albedo if τext = 0.7 at 5000 Å. To match the increase in albedo shortward of 3500 Å, a clear layer (containing about 7 km-am H2) is required above the Axel dust. Such a layer is also required to explain the limb brightening in the ultraviolet. These models can be used to analyze the observed equivalent widths of the visible methane bands. The analysis yields an abundance of the order of 1000 m-am CH4 in Titan's atmosphere. The derived CH4/H2 mixing ratio for Saturn is about 3.5 × 10?3 or an enhancement of about 5 over the solar ratio. 相似文献
14.
Glenn S. Orton 《Icarus》1975,26(2):142-158
Observations of Jovian limb structure at 8.11 and 8.45 microns are reported. These are used along with other limb structure and spectral data in the 8–14 micron region to derive a model of the thermal and cloud structure within the 1.0-0.01 bar pressure regime. The model is generally consistent with models derived from Pioneer 10 infrared radiometer data reported by Orton (1975b). The temperature is about 165K at 1.00 bar, 108K at 0.01 bar, and 143K at 0.03 bar. In zones, an optically opaque cloud of NH3 exists near the 143K (0.60 bar) level. A partly transparent haze of solid NH3 particles overlies the cloud. Belts are free of the cloud and have a much lower abundance of NH3 haze than the zones. The data are consistent with an NH3 gas abundance defined by saturation equilibrium, with a mixing ratio of 1.5 × 10?4 deep in the atmosphere, and with a CH4 mixing ratio of 2 × 10?3, about three times the currently accepted value. 相似文献
15.
Although lightning has not yet been observed in Titan's atmosphere, the presence of condensable vapors and the deposition of a significant amount of solar energy at the surface suggest the possibility of lightning activity. Based on an understanding of the relationship of lightning activity to the amount of convective energy available on Titan, a lightning energy dissipation rate of 4 × 10?6, W/m2 can be expected. This value is much lower than that for Earth or Jupiter, and is a result of both the reduced solar flux at Titan and the absorption of sunlight by the aerosols that lie above the convective layer. For this dissipation rate, the amount of HCN and C2N2 produced by lightning should be greater than that by solar UV, but could be less than that produced by electron precipitation and galactic cosmic rays. Equilibrium calculations indicate that large mole fractions of elemental solid phase carbon will also be produced. Using a simplified model of aerosol formation, coagulation, and settling, it is estimated that a lightning-produced aerosol could have a typical optical depth of 10?2, with values as high as 0.1. The accumulation of soot over geological time might reach a meter or more in depth. 相似文献
16.
V.A. Krasnopolsky 《Planetary and Space Science》1983,31(11):1363-1369
In an updating of energy characteristics of lightnings on Venus obtained from Venera-9 and -10 optical observations, the flash energy is given as 8 × 108 J and the mean energy release of lightnings is 1 erg cm?2 s which is 25 times as high as that on the Earth. Lightnings were observed in the cloud layer. The stroke rate in the near-surface atmosphere is less than 5 s?1 over the entire planet if the light energy of the stroke exceeds 4 × 105 J and less than 15 s?1 for (1–4) × 105 J.The average NO production due to lightnings equals 5 × 108 cm?2 s?1, the atomic nitrogen production is equal to 7 × 109 cm?2s?1,the N flux toward the nightside is 3.2 × 109 cm?2s?1, the number densities [N] = 3 × 107cm?3 and [NO] = 1.8 × 106cm?3 at 135 km. Almost all NO molecules in the upper atmosphere vanish interacting with N and the resulting NO flux at 90-80 km equals 5 × 105cm?2s?1, which is negligibly small as compared with lightning production. If the predissociation at 80–90 km is regarded as the single sink of NO, its mixing ratio, fNO, is 4 × 10?8, for the case of a surface sink fNO = 0.8 × 10?9 at 50 km. Excess amounts, , may exist in the thunderstorm region. 相似文献
17.
V.A. Krasnopolsky 《Icarus》1975,24(1):28-35
Altitude dependences of [CO2] and [CO2+] are deduced from Mariner 6 and 7 CO2+ airglow measurements. CO2 densities are also obtained from ne radio occultation measurements. Both [CO2] profiles are similar and correspond to the model atmosphere of Barth et al. (1972) at 120 km, but at higher altitudes they diverge and at 200–220 km the obtained [CO2] values are three times less the model. Both the airglow and radio occultation observations show that a correction factor of 2.5 should be included into the values for solar ionization flux given by Hinteregger (1970). The ratio of [CO2+]/ne is 0.15–0.2 and, hence, [O]/[CO2] is ～3% at 135 km. An atmospheric and ionospheric model is developed for 120–220 km. The calculated temperature profile is characterized by a value of T ≈ 370°K at h ? 220 km, a steep gradient (～2°/km) at 200-160 km, a bend in the profile at 160 km, a small gradient (～0.7°/km) below and a value of T ≈ 250°K at 120 km. The upper point agrees well with the results of the Lyman-α measurements; the steep gradient may be explained by molecular viscosity dissipation of gravity and acoustical waves (the corresponding energy flux is 4 × 10?2 erg cm?2sec?1 at 180 km). The bend at 160 km may be caused by a sharp decrease of the eddy diffusion coefficient and defines K ≈ 2 × 108cm2sec?1; and the low gradient gives an estimate of the efficiency of the atmosphere heating by the solar radiation as ? ≈ 0.1. 相似文献
18.
William D. Cochran 《Icarus》1977,31(3):325-347
An analysis of the structure of the Jovian atmosphere, primarily based on center-to-limb variations (CTLV) of the equivalent width of the hydrogen quadrupole 4-0 S(1) line, is presented. These data require that the atmosphere have regions of both long- and short- scattering mean free paths. Two alternative cloud structures which fit the data are developed. The first is a two-cloud model (TCM) consisting of a thin upper cloud and a lower semi-infinite cloud, with absorbing gas between the clouds and above the upper cloud. The second model is a reflecting-scattering model (RSM), in which a gas layer lies above a haze consisting of scattering particles and absorbing gas. The cloud-scattering phase function in both models must have a strong forward peak. The CTLV data require, however, the presence of a backscattering lobe on the phase function, with the backscattering intensity about 4% of the forward scattering. The decrease in reflectivity of all regions from the visible to the ultraviolet is explained by the presence of dust particles mixed with the gas. Most of the ultraviolet absorption in the atmosphere must occur above the upper cloud layer. Particles with a uniform distribution of radii from 0.0 to 0.1 μm with a complex index of refraction varying as λ?2.5 are used. The contrast in reflectivity between belts and zones may be explained by the larger concentration of dust in the belts than in the zones. Spatially resolved ultraviolet limb-darkening curves will help to determine the dust distribution of the Jovian atmosphere. The visible methane bands at λλ 6190, 5430, and 4860 Å are analyzed in terms of these models. We derive a methane-to-hydrogen mixing ratio of 2.8 × 10?3, which is about 4.5 times the value for solar composition. 相似文献
19.
V.A. Krasnopolsky 《Icarus》1979,37(1):182-189
Observations and model calculations of water vapor diffusion suggest that about half the amount of water vapor is distributed with constant mixing ratio in the Martian atmosphere, the other half is the excess water vapor in the lower troposphere. During 24 hr the total content of water vapor may vary by a factor of two. The eddy diffusion coefficient providing agreement between calculations and observations is K = (3–10) × 106 cm2 sec?1 in the troposphere. An analytical expression is derived for condensate density in the stratosphere in terms of the temperature profile, the particle radius r, and K. The calculations agree with the Mars 5 measurements for r = 1.5 μm, condensate density 5 × 10?12 g/cm3 in the layer maximum at 30 to 35 km, condensate column density 7 × 10?6 cm?2, K = (1?3) × 106 cm2 sec?1, and the temperature profile T = 185 ? 0.05z ? 0.01z2 at 20 to 40 km. Condensation conditions yield a temperature of 160°K at 60 km in the evening; the scale height for scattered radiation yields T = 110°k at 80 to 90 km. The Mars model atmosphere has been developed up to 125 km. 相似文献
20.
Marcel Nicolet 《Planetary and Space Science》1975,23(4):637-649
Nitric oxide is formed in the atmosphere through the ionization and dissociation of molecular nitrogen by galactic cosmic rays. One NO molecule is formed for each ion pair produced by cosmic ray ionization.The height-integrated input (day and night) to the lower stratosphere is of the order of 6 × 107 NO molecules cm?2/sec in the auroral zone (geomagnetic latitude Φ ? 60°) during the minimum of the sunspot cycle and 4 × 107 NO molecules cm?2/sec in the subauroral belt and auroral region (Φ? 45°) at the maximum of solar activity. The tropical production is less than 10?7 NO molecules cm?2/sec above 17 km and at the equator the production is only 3 × 106NO molecules cm?2/sec. 相似文献