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1.
New characteristics of VLF chorus in the outer magnetosphere are reported. The study is based on more than 400 hours of broadband (0.3–12.5 kHz) data collected by the Stanford University/Stanford Research Institute VLF experiment on OGO 3 during 1966–1967. Bandlimited emissions constitute the dominant form of whistler-mode radiation in the region 4? L? 10. Magnetospheric chorus occurs mainly from 0300 to 1500 LT, at higher L at noon than at dawn, and moves to lower L during geomagnetic disturbance, in accord with ground observations of VLF chorus. Occurrence is moderate near the equator, lower near 15°, and maximum at high latitudes (far down the field lines). The centre frequency ? of the chorus band varies as L?3> and at low latitudes is closely related to the electron gyrofrequency on the dipole field line through the satellite. Based on the measured local gyrofrequency ?H, the normalized frequency distribution of chorus observed within 10° of the dipole equator shows two peaks, at ??H ? 0.53 and ??H ? 0.34. This bimodal distribution is a persistent statistical feature of near equatorial chorus, independent of L, LT and Kp. However there is considerable variability in individual events, with chorus often observed above, below, and between these statistical peaks; in particular, it is not unusual for single emissions to cross ??H = 0.50. When two bands are simultaneously present individual emission elements only rarely show one-to-one correlation between bands. For low Kp the median bandwidth of the upper band, gap and lower band are all ~16% of their centre frequencies, independent of L; for higher Kp the bandwidth of the lower band increases. Bandwidth also increases with latitude beyond ~10°. Starting frequencies of narrowband emissions range throughout the band. The majority of the emissions rise in frequency at a rate between 0.2 and 2.0 kHz/sec; this rate increases with Kp and decreases with L. Falling tones are rarely observed at dipole latitudes <2.5°. The observations are interpreted in terms of whistler-mode propagation theory and a gyroresonant feedback interaction model. An exact expression is derived for the critical frequency, ??H ? 0.5, at which the curvature of the refractive index surface vanishes at zero wave normal angle. Near this frequency rays with initial wave normal angles between 0° and ?20° are focused along the initial field line for thousands of km, enhancing the phase-bunching of incoming gyroresonant electrons. The upper peak in the bimodal normalized frequency distribution is attributed to this enhancement near the critical frequency, at latitudes of ~5°. Slightly below the critical frequency interference between modes with different ray velocities may contribute to the dip in the bimodal distribution. The lower peak may reflect a corresponding peak in the resonant electron distribution, or guiding in field-aligned density irregularities. The observations are consistent with gyroresonant generation of emissions near the equator, followed by spreading of the radiation over a range of L shells farther down the field lines.  相似文献   

2.
The combination of a small inclination of the orbit (~4°) with the tilt angle (~11°) of the Earth's magnetic dipole axis enabled the S3-A satellite (Explorer 45) to make simultaneous observations of magnetospheric VLF-emissions and the associated enhancement of ring current electrons not only at the magnetic equator but also up to 15° geomagnetic latitudes. Microdensitometer scanning of the wideband data of these emissions reveals that the band of missing emission in the off-equatorial whistler mode emissions (chorus) appears at fHo2 and that the intensities of the off-equatorial emission above fHo2 are very weak in contrast to those of the near equatorial emissions, where fHo2 is the equatorial electron gyrofrequency corresponding to the local gyrofrequency fH at the satellite. Ray-tracing of whistler mode waves produced by the enhanced ring-current electrons at the geomagnetic equator just outside of the plasmapause has shown that some of these waves are reflected from high latitudes back to the Equator inside the source region. This process had been previously speculated to explain the formation of the bimodal intensity distribution with a gap at half the gyrofrequency (the two-band chorus) in the equatorial emission data. The intensities of those reflected waves, however, are shown to be insufficient to explain the observed emissions below fHo2 at the Equator. These results indicate that the superposition of two types of emissions produced by the same processes but from different locations is not the main mechanism for the formation of the two-band chorus and that the dominant sources of these choruses are located around ± 5° geomagnetic latitude.  相似文献   

3.
Magnetic-field aligned currents driven by plasma pressure inhomogeneities (plasma clouds) in the distant magnetosphere are analyzed quantitatively. A parallel potential drop is found to be established in the upward current region whenever a spatial scale D0 for the pressure gradient in the equatorial magnetosphere is smaller than ≈ 3g0BiB0, where g0 is a hot electron gyroradius in the equatorial magnetic field B0 (Bi denotes the magnetic induction in the ionosphere). A theoretical derivation is given for the experimentally observed linear relation T = AEp + T0 between the characteristic energy T of precipitating magnetospheric electrons and the peak energy Ep in inverted-V electron spectra. Three-dimensional potential structures accelerating electrons earthward are shown to be established beneath some model clouds which could correspond to a large scale inverted-V structure and to a thin (~ 1 km) auroral arc.  相似文献   

4.
5.
The paper gives the results of detailed studies of the frequency spectra Ss(?) 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 ?s0 of spectra—the carrier frequencies of the signals. The velocity V0 ≌ 6.103km s?1 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 ? = 2?s0and 3?s0 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 ?±sK. Frequency differences Δ?sK± = ¦?s0 ? ?sK±¦ = (0.011,0.022 and 0.035) Hz 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   

6.
The launch of the P78-2 (SCATHA) satellite in January 1979 has provided a new opportunity to study the energetic ion composition in the high altitude equatorial regions of the earth's magnetosphere. In particular detailed pitch angle distributions were obtained as a function of ion species and energy. The energies measured range from ~ 90 to 250 keV/nucleon for Z ? 2. Data are presented which were acquired in late March and early April 1979. The relative abundance of He and CNO nuclei are found to be ~ 10?2 and 5 × 10?4 respectively at L ? 5.5. Only an upper limit on the relative abundance of Fe group nuclei of < 3 × 10?7 was obtained. The angular distributions of the heavy ions was found to be very steep for BB0 < 1.5 and then to flatten markedly.  相似文献   

7.
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 fH ? 10?10 to depress ozone concentrations below the observed upper limit in equatorial regions. Another catalytic reaction that should be driven by photodesorption on Mars is 20H?(ads)H2O + 12O2(g) + 2e?crystal. 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   

8.
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 ? ? (0.5?2.5) Hz 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 L ? 3?10. 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 ΩH everywhere along its propagation trajectory, including the apogee of the magnetic force line (ΩH is the proton gyrofrequency). Proton flux spectra E ? (30?120) 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 Np(MV622) ? (5 × 10?3?10?1) Ha2 where Ha is the magnetic field force in the generation region of these W.P. The electron concentration is Na ? (102?103) cm?3. The values given in the literature are Na ? (10?10?103) cm?3. 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   

9.
An attempt has been made to estimate the east-west component (Ew) of the magnetospheric equatorial electric field near L = 1.12 during a magnetic storm period from the whistlers observed at our low latitude ground station, Nainital (geomag.lat. 19°1'N), on March 25, 1971 in the 0130–0500 IST sector. The method of measuring Ew from the observed cross L-motions of whistler ducts within the plasmasphere, indicated by changes in nose frequency of whistlers, has been outlined. The nose frequencies of non-nose whistlers under consideration have been deduced from Dowden-Allcock linear Q-technique. The variation of (?n)23 with local time has been shown, the slope of which can be directly related to the convection electric field. The estimated equatorial electric field at L? 1.12 is in the range 0.1–0.5 mV m?1 (in the 0130–0500 IST sector) during a storm period, which is in agreement with the results reported by earlier workers. The departure from a dipole field and the contribution of an induced electric field from the temporal changes have been discussed. The importance of an electric field study has been indicated.  相似文献   

10.
Daytime Pc 3–4 pulsation activities observed at globally coordinated low-latitude stations [SGC (L = 1.8,λ = 118.0°W), EWA(1.15,158.1°W), ONW(1.3,141.5°E)] are evidently controlled by the cone angle θXB of the IMF observed at ISEE 3. Moreover, the Pc 3–4 frequencies (?) at the low latitudes and high latitude (COL; L = 5.6 and λ = 147.9°W) on the ground and that of compressional waves at geosynchronous orbit (GOES 2; L = 6.67 and λ = 106.7°W) are also correlated with the IMFmagnitude(BIMF).The correlation of ? of the compressional Pc 3–4 waves at GOES 2 against BIMF is higher than those of the Pc 3–4 pulsations at the globally coordinated ground stations, i.e., γ = 0.70 at GOES 2, and (0.36,0.60,0.66,0.54) at (COL, SGC, EWA, ONW), respectively. The standard deviation (σn = ± Δ? mHz) of the observed frequencies from the form ? (mHz) = 6.0 × BIMF (nT) is larger at the ground stations than at GOES 2, i.e., Δ? = ± 6.6 mHz atGOES 2, and ±(13.9, 9.1, 10.7, 12.1) mHz at (COL, SGC, EWA, ONW), respectively. The correlations between the IMF magnitude BIMF and Pc 3–4 frequencies at the low latitudes are higher than that at the high latitude on the ground, which can be interpreted by a “filtering action” of the magnetosphere for daytime Pc 3–4 magnetic pulsations. The scatter plots of pulsation frequency ? against the IMF magnitude BIMF for the compressional Pc 3–4 waves at GOES 2 are restricted within the forms ? = 4.5 × BIMFand ? = 7.5 × BIMF. The frequency distribution is in excellent agreement with the speculation (scΩi = 0.3 ~ 0.5) of the spacecraft frame frequency of the magnetosonic right-hand waves excited by the anomalous ion cyclotron resonance with reflected ion beams with V6 = 650 ~ 1150 km s?1 in the solar wind frame observed by the ISEE satellite in the Earth's foreshock. These observational results suggest that the magnetosonic right-handed waves excited by the reflected ion beams in the Earth's foreshock are convected through the magnetosheath to the magnetopause, transmitted into the magnetosphere without significant changes in spectra, and then couple with various HM waves in the Pc 3–4 frequency range at various locations in the magnetosphere.  相似文献   

11.
The photodissociation of water vapour in the mesosphere depends on the absorption of solar radiation in the region (175–200 nm) of the O2 Schumann-Runge band system and also at H-Lyman alpha. The photodissociation products are OH + H, OH + H, O + 2H and H2 + O at Lyman alpha; the percentages for these four channels are 70, 8, 12 and 10%, respectively, but OH + H is the only channel between 175 and 200 nm. Such proportions lead to a production of H atoms corresponding to practically the total photodissociation of H2O, while the production of H2 molecules is only 10% of the H2O photodissociation by Lyman alpha.The photodissociation frequency (s?1) at Lyman alpha can be expressed by a simple formula
JLyαH2O=4.5 ×10?61+0.2F10.7?65100exp[?4.4 ×10?19 N0.917]
where F10.7 cm is the solar radioflux at 10.7 cm and N the total number of O2 molecules (cm?2), and when the following conventional value is accepted for the Lyman alpha solar irradiance at the top of the Earth's atmosphere (Δλ = 3.5 A?) qLyα,∞ = 3 × 1011 photons cm?2 s1?.The photodissociation frequency for the Schumann-Runge band region is also given for mesospheric conditions by a simple formula
JSRB(H2O) = JSRB,∞(H2O) exp [?10?7N0.35]
where JSRB,∞(H2O) = 1.2 × 10?6 and 1.4 × 10?6 s?1 for quiet and active sun conditions, respectively.The precision of both formulae is good, with an uncertainty less than 10%, but their accuracy depends on the accuracy of observational and experimental parameters such as the absolute solar irradiances, the variable transmittance of O2 and the H2O effective absorption cross sections. The various uncertainties are discussed. As an example, the absolute values deduced from the above formulae could be decreased by about 25-20% if the possible minimum values of the solar irradiances were used.  相似文献   

12.
R.D. Cess  S.C. Chen 《Icarus》1975,26(4):444-450
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 [C2H6][H2] = 10?5 and [C2H2][H2] = 5 × 10?7, 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   

13.
T.E. Cravens  A.E.S. Green 《Icarus》1978,33(3):612-623
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+ (A?2A1?X?2B1), CO+ (first negative), CO (fourth positive), CO (Cameron), CO2+ (B?2?u?X?2IIg), 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   

14.
Rosseland mean opacities a?R(T,lgPe) [see Table 2] per unit hydrogen particle are calculated in this paper for the atmosphere of the solar type [see Table 1].The sources of the continuous opacities under consideration in this paper are as follows: (1) H?, HI, H?2, H+2 He?, HeI, HeII, CI, CII, CIII, NI, NII, NIII, OI, OII, NaI, MgI, MgII, AlI, AlII, SiI, SiII, CII, KI, CaII in the form of absorption. (2) HI, HeI, CI, NI, OI, H2 in the form of Rayleigh scattering. (3) Free electrons in the form of Thomson scattering.  相似文献   

15.
《Planetary and Space Science》1987,35(8):1009-1020
Latitudinal structures of discrete arcs are modelled as a consequence of the quasi-steady magnetosphere-ionosphere coupling involving viscous interaction between sunward and anti-sunward plasma flows in the magnetosphere. The quasi-steady state in the magnetosphere and ionosphere coupling is described by the magnetospheric and ionospheric current conservation and the field-aligned currentpotential relation assuming adiabatic electron motion along field lines. The upward and downward fieldaligned currents are assumed to be stably maintained by vorticity-induced space charges in the region of plasma flow reversal, where divergence of the magnetospheric electric field E is negative and positive, respectively. By introducing the effective conductance Σdc arising from the anomalous viscosity, a specific relation between the dc field-aligned current density J and the magnetospheric electric field E is derived as J=−ΣdcdivE. Sufficiently large potential drops to accelerate auroral electrons are shown to exist along the auroral field lines originating from the flow reversal region with div E < 0. It is shown that the latitudinal structure of a discrete arc is primarily determined by the magnetospheric potential structure and the characteristic width is on the order of 10 km at the ionospheric altitude.  相似文献   

16.
A qualitative model of the negative phase of ionospheric storms is presented. Only stations located within an atmospheric disturbance zone of a low ON2 ratio will observe a depletion of ionization. The extent of this disturbance zone is determined by geomagnetic coordinates. Thus stations located in the North American and Australian sectors are more liable to observe negative storm effects. On the other hand it is determined by the asymmetric energy injection along the auroral oval. It follows that stations located in the early morning sector during enhanced substorm activity have a greater chance of observing negative storm effects than those situated in the daytime sector. Seasonal and magnetic storm induced changes in the ON2 ratio are in phase during summer and out of phase during winter, explaining the seasonal variation of storm effects.  相似文献   

17.
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 X1 Σg+ ground state to a continuum level of the X2 Σg+ 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   

18.
There is a magnetosonic waveguide under the arch of the plasmasphere. This channel, in the form of a ring with radius L~4, surrounds the Earth. It is shown that in this region of the magnetosphere the flute-like electromagnetic disturbances (k6 = 0) with frequencies ω = p can be excited by energetic protons, with non-monotonic dependence on transverse energy (??/?ε > 0). The interpretation of magnetic pulsations which have been observed in the equatorial vicinity of the plasmapause on the satellite OGO-3 in the frequency range ~102 cps (Russell et al., 1970) is given. In particular the origin of discrete structure of the observed spectra (narrow band spikes for a rather broad range of frequency) is discussed.  相似文献   

19.
A significant sink of geomagnetic pulsation energy is due to Joule dissipation in the ionosphere. To investigate this we have computed the damping experienced by standing Alfvén waves in a dipole magnetic field. Both the uncoupled poloidal and toroidal modes are considered with Joule dissipation being introduced through a boundary condition which relates the electric and magnetic field strengths at the ionosphere, viz: 4πΣ pEc = b, where Σp is the height integrated Pederson conductivity. The damping rates are strongly dependent on the ionospheric conductivity and we find that typically the normalized damping rate, γω, is ~0.1 for nightside values of conductivity and ~0.01 for the dayside. This would account for the observed scale of bandwidths in pulsation signals. Away from regions of extreme damping we find γL?1Σp?1.  相似文献   

20.
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