共查询到20条相似文献，搜索用时 31 毫秒
1.
The quenching rate kN2 of by N2 and the specific recombination rate α1D of O2+ leading to are re-examined in light of available laboratory and satellite data. Use of recent experimental values for the transition probabilities in a re-analysis of AE-C satellite 6300 Å airglow data results in a value for kN2 of 2.3 × 10?11 cm3s?1 at thermospheric temperatures, in excellent agreement with the laboratory measurements. This implies a value of JO2 = 1.5 × 10?6s?1 for the O2 photodissociation rate in the Schumann-Runge continuum. The specific recombination coefficient α1D = 2.1 × 10?7cm3s?1 is also in agreement with the laboratory value. Implications for the suggested reaction are discussed. 相似文献
2.
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
3.
A mechanism has been proposed for uv-accelerated desorption from Fe2+ sites on mineral surfaces that satisfies kinetic constraints determined in the laboratory by Huguenin. The process is an integral step of the photochemical weathering mechanism for producing dust on Mars, and it now appears that it may play primary roles in stabilizing CO2 against dissociation by sunlight and in controlling the oxidation state of the atmosphere. We propose that adsorption occurs at octahedrally coordinated Fe2+ surface sites to form seven-coordinate transition-state complexes. These complexes acquire 16–18 kcal mole?1 of ligand field stabilization energy. During illumination (λ ≤ 0.35 μm), electrons are photoemitted from the surfaced Fe2+, temporarily oxidizing them to Fe3+. Fe3+ has no ligand field stabilization energy, and the complexes lose 16–18 kcal mole?1 of stabilization energy. This is a large fraction of the 19- to 28-kcal mole?1 activation energy for dissociating the complexes, and desorption should proceed spontaneously. The gases that were observed to undergo adsorption-photodesorption include O2, CO2, CO, H2O, N2, and Ar. Photodesorption can drive several catalytic reactions, one of which is the oxidation of CO to CO2. The rate of this reaction should be limited by the supply of CO and O2 to the surface to ～2 × 1012 cm?2 sec?1 (column photodissociation rate of CO2). By including this surface reaction in models of Martian atmospheric CO2 chemistry, CO2 can be stabilized against photodissociation with eddy diffusion coefficients of only 3 × 105?1 × 107 cm2 sec?1 below 40 km, raising to ～ 109 cm2 sec?1 at 140 km. Odd hydrogen is not needed to catalyze the oxidation of CO below 40 km, and odd hydrogen mixing ratios need only to be to depress ozone concentrations below the observed upper limit in equatorial regions. Another catalytic reaction that should be driven by photodesorption on Mars is . This is an important source of atmospheric O2, amounting to 7 × 1013?2 × 1017 O2 molecules cm?2 yr?1, and it could have a significant effect on atmospheric oxidation state. 相似文献
4.
Recent laboratory measurements of the deactivation rate constants for O(1S) have suggested that the dominant production mechanism for the green line in the nightglow is a two-step process. A similar mechanism involving energy transfer from an excited state of molecular oxygen is considered as a potential source of the OI (5577 Å) emission in the aurora. It is shown that the mechanism, , is consistent with auroral observations; the intermediate excited state has been tentatively identified as the O2(c1∑?u) state. For the proposed energy transfer mechanism to be the primary source of the auroral green line, the peak electron impact cross-section for O21 production must be approximately 2 × 10?17 cm2. 相似文献
5.
Previous studies based on radio scintillation measurements of the atmosphere of Venus have identified two regions of small-scale temperature fluctuations located in the vicinity of 45 and 60 km. A global study of the fluctuations near 60 km, which are consistent with wind-shear-generated turbulence, was conducted using the Pioneer Venus measurements. The structure constants of refractive index fluctuations cn2 and temperature fluctuations cT2 increase poleward, peak near 70° latitude, and decrease over the pole; cn2 varies from 2 × 10?15 to 1.5 × 10?14m and cT2 from 4 × 10?3 to 7 × 10?2°K2m. These results indicate greater turbulent activity at the higher latitudes. In the region near 45 km the refractive index fluctuations and the corresponding temperature fluctuations are substantially lower. Based on the analysis of one representative occultation measurement, in the 45-km region. The fluctuations in this region also appear to be consistent with wind-shear-generated turbulence. The turbulence level is considerably weaker than that at 60 km; the energy dissipation rate ε is 4.9 × 10?5m2sec?3 and the small-scale eddy diffusion coefficient K is 2 × 103 cm2 sec?1. 相似文献
6.
Measurements of N2+ and supporting data made on the Atmosphere Explorer-C satellite in the ionosphere are used to study the charge exchange process The equality k = (5 ± 1.7) × 10?10cm3s?1. This value lies close to the lower limit of experimental uncertainty of the rate coefficient determined in the laboratory. We have also investigated atomic oxygen quenching of O+(2D) and find that the rate coefficient is 2 × 10?11 cm3s?1 to within approximately a factor of two. 相似文献
7.
K.M. Monahan W.T. Huntress A.L. Lane J.M. Ajello T.E. Burke P. Le Breton A. Williamson 《Planetary and Space Science》1974,22(1):143-149
The cross-section for dissociative photoionization of hydrogen by 584 Å radiation has been measured, yielding a value of 5 × 10?20 cm2. The process can be explained as a transition from the ground state to a continuum level of the ionized state of H2 The branching ratio for proton (H+) vs molecular ion (H2+) production at this energy is 8 × 10?3. This process is quite likely an important source of protons in the Jovian ionosphere near altitudes where peak ionization rates are found. 相似文献
8.
The intensities of radiation from the inner comas of comets which are composed primarily of water and carbon monoxide have been calculated. Only “airglow” emissions initiated by the absorption of extreme ultraviolet radiation have been considered. The photoionizations of H2O, CO, CO2, and N2 are the most important emission sources, although photoelectron excitation is also considered. Among the emission features for which intensities were calculated are H2O+ (), CO+ (first negative), CO (fourth positive), CO (Cameron), CO2+ (), N2 (Vegard-Kaplan), N2+ (first negative), and OI (1304 Å). In the inner coma (collision region) these airglow mechanisms are shown to be possible competitors with the usually assumed resonance scattering and flourescence excitation mechanisms which are appropriate for the outer coma and tail. 相似文献
9.
We calculate the Love numbers kn for n = 2 to 10, and determine the “gravitational noise” from tides. The new values k2 for Jupiter, Saturn, and Uranus yield new estimates for the planetary dissipation functions: , . 相似文献
10.
11.
Ethane and acetylene, both of which possess more efficient emission bands than methane, have been incorporated into a thermal structure model for the atmosphere of Jupiter. Choosing for illustrative purposes the mixing ratios and , it is found that these hydrocarbon gases lower the atmospheric temperature within the thermal inversion region by as much as 20 K, subsequently reducing the emission intensity of the 7.7 μm CH4 band below the observed result. It is qualitatively shown, however, that this cooling by C2H6 and C2H2 could be compensated by aerosol heating resulting from a uniformily mixed aerosol which absorbs 15% of the incident solar radiation. Such aerosol heating has been suggested by uv albedo observations. 相似文献
12.
Results are given of the calculations of the group delay time propagating τ(ω, φ0) of hydromagnetic whistlers, using outer ionospheric models closely resembling actual conditions. The τ(ω, φ0) dependencies were compared with the experimental data of τexp(ω, φ0) obtained from sonagrams. The sonagrams were recorded in the frequency range at observation points located at geomagnetic latitudes φ0 = (53?66)° and in the vicinity of the geomagnetic poles. This investigation has led us to new and important conclusions.The wave packets (W.P.) forming hydromagnetic whistlers (H.W.) are mainly generated in the plasma regions at L = 3.5?4.0. This is not consistent with ideas already expressed in the literature that their generation region is . The overwhelming majority of the τexp values differ considerably from the times at which wave packets would, in theory, propagate along the magnetic field lines corresponding to those of the geomagnetic latitudes φ0 of the observation points. The second important fact is that the W.P. frequency ω is less than everywhere along its propagation trajectory, including the apogee of the magnetic force line ( is the proton gyrofrequency). Proton flux spectra keV, responsible for H.W. generation, were determined. Comparison of the Explorer-45 and OGO-3 measurements published in the literature, with our data, showed that the proton flux density energy responsible for the H.W. excitation where Ha is the magnetic field force in the generation region of these W.P. The electron concentration is . The values given in the literature are . The e data considered also leads to the conclusion that the generating mechanism of the W.P. studied probably always co-exists with the mechanism of their amplification. 相似文献
13.
Models of the collapse of a protostellar cloud and the formation of the solar nebula reveal that the size of the nebula produced will be the larger of (where J, M, and cs are the total angular momentum, total mass, and sound speed of the protosetellar material; G is the gravitational constant; k is a number of order unity; and v is the effective viscosity in the nebula). From this result it can be deduced that low-mass nebulas are produced if P ≡ (RV/RCF)2 ? 1; “massive” nebulas result if P ? 1. Gravitational instabilities are expected to be important for the evolution of P ? 1 nebulas. The value of J distinguishes most current models of the solar nebula, since P ∝ J?4. Analytic expressions for the surface density, nebular mass flux, and photospheric temperature distributions during the formation stage are presented for some simple models that illustrate the general properties of growing protostellar disks. It does not yet seem possible to rule out either P ? 1 or P < 1 for the solar nebula, but observed or possible heterogeneities in composition and angular-momentum orientation favor P < 1 models. 相似文献
14.
Incoherent scatter observations of the ionospheric F1 layer above Saint-Santin (44.6°N) are analyzed after correction of a systematic error at 165 and 180 km altitude. The daytime valley observed around 200 km during summer for low solar activity conditions is explained in terms of a downward ionization drift which reaches ?30 m s?1 around 180 km. Experimental determinations of the ion drift confirm the theoretical characteristics required for the summer daytime valley as well as for the winter behaviour without a valley. The computations require an effective dissociative recombination rate of and ionizing fluxes compatible with solar activity conditions at the time when the valley is observed. 相似文献
15.
Radiative recombination of N and O provides a significant source for auroral emission in the γ and δ bands of NO with selective population of vibrational levels in the A2Σ+ and C2Π states. This mechanism may account for emissions detected near 2150 Å. Models are derived for the auroral ionosphere and include estimates for the concentrations of N and NO. The concentration of NO is estimated to have a value of about 108 cm?1 near 140 km in an IBC III aurora. The corresponding density for N is about 5 × 107cm?3 and the concentration ratio has a value of about 5.5. 相似文献
16.
The paper gives the results of detailed studies of the frequency spectra of the chain of the wave packets Fs(t) of geomagnetic pulsations PC-1 recorded at the Novolazarevskaya station. The bulk of the energy of Fs(t) is concentrated in the vicinity of the central frequencies of spectra—the carrier frequencies of the signals. The velocity of the flux of protons generating these signals correspond to them. The spectra of the signals have oscillations—“satellites” irregularly distributed in frequency. These satellites, as the authors believe, testify to the presence of the individual groups of protons of low concentration whose velocities vary within 103–104 km s?1.Their energy is only of the order of 10?2–10?3 of the energy of the main proton flux. Clearly pronounced maxima on double and triple frequencies are detected. They show that the generation of pulsations PC-1 is accompanied by the generation on the overtones of wave packets called in this paper “two-fold” and “three-fold” pulsations PC-1. Intensive symmetrical satellites of a modulation character have been discovered on frequencies . Frequency differences correspond to them. The authors believe that the values of Δ?±sK are resonance frequencies of the magnetospheric cavity in which geomagnetic pulsations PC-1 are generated. It is established that the values of Δ?±sK coincide closely with the carrier frequencies of geomagnetic pulsations PC-3 and PC-4 generated in the magnetosphere. This leads to the conclusion that the resonance oscillations of the magnetospheric cavity are their source. Thus, the generation of geomagnetic pulsations of different types and resonance oscillations in the magnetosphere are integrated into a unified process. The importance of the results obtained and the necessity to check further their trustworthiness and universality, using experimental data gathered in different conditions, is stressed. 相似文献
17.
In this paper we confirm an earlier finding that the reaction constitutes a major source of OI 6300 Å dayglow. The rate coefficient for this reaction is found to be consistent with an auroral result, namely k1 ≈ 6 × 10?12cm3s?1. We correct an error in an earlier publication and demonstrate that reaction (1) is consistent with the laboratory determined quenching rate for the reaction where . Dissociative recombination of O+2 with electrons is found to be a major daytime source in summer above ～220 km. 相似文献
18.
Joseph A. Burns 《Icarus》1981,45(1):1-3
The Galilean satellites Io, Europa, and Ganymede interact through several stable orbital resonances where and λ1 ? 3λ2 + 2λ3 = 180°, with λi being the mean longitude of the ith satellite and the longitude of the pericenter. The last relation involving all three bodies is known as the Laplace relation. A theory of origin and subsequent evolution of these resonances outlined earlier (C. F. Yoder, 1979b, Nature279, 747–770) is described in detail. From an initially quasi-random distribution of the orbits the resonances are assembled through differential tidal expansion of the orbits. Io is driven out most rapidly and the first two resonance variables above are captured into libration about 0 and 180° respectively with unit probability. The orbits of Io and Europa expand together maintaining the 2:1 orbital commensurability and Europa's mean angular velocity approaches a value which is twice that of Ganymede. The third resonance variable and simultaneously the Laplace angle are captured into libration with probability ～0.9. The tidal dissipation in Io is vital for the rapid damping of the libration amplitudes and for the establishment of a quasi-stationary orbital configuration. Here the eccentricity of Io's orbit is determined by a balance between the effects of tidal dissipation in Io and that in Jupiter, and its measured value leads to the relation with the k's being Love numbers, the Q's dissipation factors, and f a factor to account for a molten core in Io. This relation and an upper bound on Q1 deduced from Io's observed thermal activity establishes the bounds 6 × 104 < QJ < 2 × 106, where the lower bound follows from the limited expansion of the satellite orbits. The damping time for the Laplace libration and therefore a minimum lifetime of the resonance is 1600 QJ years. Passage of the system through nearby three-body resonances excites free eccentricities. The remnant free eccentricity of Europa leads to the relation for rigidity μ2 = 5 × 1011 dynes/cm2. Probable capture into any of several stable 3:1 two-body resonances implies that the ratio of the orbital mean motions of any adjacent pair of satellites was never this large.A generalized Hamiltonian theory of the resonances in which third-order terms in eccentricity are retained is developed to evaluate the hypothesis that the resonances were of primordial origin. The Laplace relation is unstable for values of Io's eccentricity e1 > 0.012 showing that the theory which retains only the linear terms in e1 is not valid for values of e1 larger than about twice the current value. Processes by which the resonances can be established at the time of satellite formation are undefined, but even if primordial formation is conjectured, the bounds established above for QJ cannot be relaxed. Electromagnetic torques on Io are also not sufficient to relax the bounds on QJ. Some ideas on processes for the dissipation of ideal energy in Jupiter yield values of QJ within the dynamical bounds, but no theory has produced a QJ small enough to be compatible with the measurements of heat flow from Io given the above relation between Q1 and QJ. Tentative observational bounds on the secular acceleration of Io's mean motion are also shown not to be consistent with such low values of QJ. Io's heat flow may therefore be episodic. QJ may actually be determined from improved analysis of 300 years of eclipse data. 相似文献
19.
20.
A magnetic type mass spectrometer has been flown on two ESRO sounding rockets from ESRANGE (Kiruna 68°N) on February 25 and 26, 1970. The first launch was at sunset (16:33 UT) and the second the next morning, during sunrise (04:47 UT). For both flights the solar zenith angle was approximately 98°. The instrument was measuring simultaneously the neutral gas and positive ion composition and the total ion density. In this paper the results of the ion composition measurements are presented. For both flights the main ion constituents measured between approximately 110–220 km were O+, NO+ and O2+. Only at sunset were N+ and N2+ detected above 200 km. In spite of the identical solar UV-radiation, pronounced sunset/sunrise variations in the positive ion composition were found. The total ion densities at sunrise were between 5×103 and 5 × 104 ions cm?3 and therefore too high to be explained without a night-time ionization by precipitated particles. At sunrise the NO+ and O2+ profiles show a correlated wavelike structure with three pronounced almost equally spaced layers in the E-region. Only the highest layer is present in the O+ profile. Locally enhanced field aligned ionization originated by particle precipitation and an E × B instability are the most likely source for this structure. In the E- and lower F-regions the ration increased overnight from values around 7 at sunset to 15 at sunrise, correlated with an increase of the local magnetic activity index K from 0+ to 2°. This could be explained if the NO density and magnetic activity are correlated. 相似文献