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1.
In this paper, by comparing experimental data on bow shock with MHD-relationships on a flat shock discontinuity, allowing for the presence behind the front of turbulent electrostatic oscillations and of an ion beam, an analysis is made of the nature of the “overshoot” of magnetic field (density) behind the front of a collisionless shock wave. It is shown that the large value of plasma compression in the overshoot region (n2ovn1) ~ 6, in excess of the maximum allowable value of density jump (n2n1)|max = (γ + 1γ ? 1)|γ = 53 = 4 at a Mach numberM → ∞, is attributable to the presence in the “overshoot” of a high level of lowerhybrid electrostatic oscillations with an energy density W ? nT.  相似文献   

2.
An astrophysical electron acceleration process is described which involves turbulent plasma effects: the acceleration mechanism will operate in ‘collision free’ magnetoactive astrophysical plasmas when ion-acoustic turbulence is generated by an electric field which acts parallel to the ambient magnetic lines of force. The role of ‘anomalous’ (ion-sound) resistivity is crucial in maintaining the parallel electric field. It is shown that, in spite of the turbulence, a small fraction of the electron population can accelerate freely, i.e. runaway, in the high parallel electric potential. The number density n(B) of the runaway electron component is of order n(B)?n2(csU?)2, where n = background electron number density, cs = ion-sound speed and U? = relative drift velocity between the electron and ion populations. The runaway mechanism and the number density n(B) do not depend critically on the details of the non-linear saturation of the ion-sound instability.  相似文献   

3.
New ion cyclotron whistlers which have the asymptotic frequency of one half the local proton gyrofrequency, Gp2, and the minimum (or equatorial) proton gyrofrequency, Gpm, along the geomagnetic field line passing through the satellite have been found in the low-latitude topside ionosphere from the spectrum analysis of ISIS VLF electric field data received at Kashima, Japan. Ion cyclotron whistlers with asymptotic frequency of Gpm or Gpm2 are observed only in the region of Bm >B2 or rarely Bm >B4, where B is the local magnetic field and Bm is the mini magnetic field along the geomagnetic field line passing through the satellite.The particles with one half the proton gyrofrequency may be the deuteron or alpha particle. Theoretical spectrograms of the electron whistlers (R-mode) and the ion cyclotron whistlers (L-mode) propagating along the geomagnetic field lines are computed for the appropriate distributions of the electron density and the ionic composition, and compared with the observed spectrograms.The result shows that the ion cyclotron whistler with the asymptotic frequency of Gp2 is the deuteron whistler, and that the ion cyclotron whistlers with the asymptotic frequency of Gpm or Gpm2 are caused by the trans-equatorial propagation of the proton or deuteron whistler from the other hemisphere.  相似文献   

4.
The thermal escape of hydrogen from the Earth's atmosphere is strongly affected by its temperature at the exobase. It has been suggested recently that the hydrogen temperature might be significantly lower than the thermospheric temperature as a result of a collisional exchange of energy with atomic oxygen. The tendency is to cool the hydrogen since the energy of the excited 3P1 level of oxygen can be lost from the atmosphere via magnetic dipole emission of the 63 μm line (3P2?3P1). We present here a detailed calculation of the net cooling effect as a function of altitude throughout the thermosphere. The calculations have been performed for both day and night conditions and for periods of maximum and minimum solar activity conditions. It is found that its effect on ΔT/T varies from a very small value to a maximum of ~3%. We also provide the theoretical framework for describing deviations of the 63 μm emission from local thermodynamic equilibrium and show that these effects can cause the emission to be reduced by as much as 40% near 500 km.  相似文献   

5.
6.
A theoretical consideration is given to the critical ionization velocity. A macroscopic theory is constructed, assuming that (1) the newly born ions have an unstable velocity distribution and (2) the resultant fluctuating electric field heats the electrons. For the critical ionization velocity to operate in the case of maV22 > eφion, the initial values of high speed ion (or newly ionized ion) density and suprathermal electron energy density should be above a certain threshold. This threshold depends upon the velocity diffusion co-efficient and the collisional loss rate of the newly ionized ion.  相似文献   

7.
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   

8.
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   

9.
The Stokes parameters of resonance radiation scattered by a Na atom with the angular momentum F aligned by directed unpolarized radiation in a magnetic field H ~ 10?5?10?1 Oe are presented. An influence of the orientation of the magnetic field on these parameters are studied; the intensity ratio I(D2)I(D1) changes within ±5%, and the polarization degree P(D2) within ±25%. Measurements of I(D2)I(D1) and P(D2), if the geometry of scattering is known, may give information on the direction of the magnetic field in the sodium atmospheres of comets, as well as Io's sodium cloud or man-made cosmic clouds.  相似文献   

10.
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   

11.
The beam cyclotron instability and electron acoustic instability, driven by cross-tail current and inhomogeneity in density and magnetic field, are found to be unstable in the earth's magnetic tail region. The anomalous resistivities due to these instabilities are found to be of the order of (10?1?10?3e?1e being the electron gyro frequency). It is also suggested that the non-linear saturation of the beam cyclotron instability may lead to conditions favourable for exciting ion acoustic instability.  相似文献   

12.
13.
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?14m23 and cT2 from 4 × 10?3 to 7 × 10?2°K2m?23. 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, cn2 = 2 × 10?16m?23and cT2 = 7.3 × 10?4°K2m?23 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   

14.
Measurements of dayglow radiance of O2(1Δg) and OH(7,2) bands are reported. Ground based photometers were used to monitor zenith radiance of 1270 and 694 nm emissions during the total solar eclipse of 16 February 1980. Altitude distribution of 1270 nm intensity was derived from ground based observations. A set of altitude distributions of O2(1Δg) were thus obtained throughout the eclipse. These altitude distributions were converted into ozone distributions using the rate equations for formation and loss of ozone and O2(1Δg) molecules. Results indicate an increase in the ozone concentration at mid-eclipse. OH(7,2) emission did not show enhancement during totality. This may mean that there was no increase in OH concentration during the eclipse.  相似文献   

15.
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   

16.
The timing of the plasma-sheet thinning relative to the onset of the expansion phase of substorms is examined by the analysis of the OGO 5 electron (79 ± 23 keV) and proton (100~150 keV) data with the aid of simultaneous magnetic field observations. It is found that the timing of the thinning is significantly dependent on the distance. At x2 + y2 ? 15 RE the thinning often starts before the onset, while at x2 + y2 ? 15 RE it tends to occur after the onset, where x and y refer to solar magnetospheric coordinates. The thinning that precedes the expansion-phase onset has been found to reduce the thickness to ~1 RE, and further thinning may occur in a spatially limited region. Hence it is conceivable that the formation of the neutral line characterizing the substorm expansion phase is the consequence of the thinning of the plasma sheet in the near-Earth region.  相似文献   

17.
S.V. Gavrilov  V.N. Zharkov 《Icarus》1977,32(4):443-449
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: QJ ? 2.5 × 104, QS ? 1.4 × 104, QU ? 5 × 103.  相似文献   

18.
Whistlers recorded at Eights (L ? 4) and Byrd (f ? 7), Antarctica have been used to study large-scale structure in equatorial plasma density at geocentric distances ?3–6 RE. The observations were made during conditions of magnetic quieting following moderate disturbance. The structures were detected by a “scanning” process involving relative motion, at about one tenth of the Earth's angular velocity or greater, between the observed density features and the observing whistler station or stations. Three case studies are described, from 26 March 1965, 11 May 1965 and 29 August 1966. The cases support satellite results by showing outlying high density regions at ?4–6 RE that are separated from the main plasmasphere by trough-like depressions ranging in width from ?0.2 to 1 RE. The structures evidently endured for periods of 12 hr or more. In the cases of deepest quieting their slow east-west motions with respect to the Earth are probably of dynamo origin. The cases observed during deep quieting (11 May 1965 and 29 August 1966) suggest the approximate rotation with the Earth of structure formed during previous moderate disturbance activity in the dusk sector. The third case, from 26 March 1965, may represent a structure formed near local midnight. The reported structures appear to be closely related to the bulge phenomenon. The present work supports other experimental and theoretical evidence that the dusk sector is one of major importance in the generation of outlying density structure. It is inferred that irregularities of the type reported here regularly develop near 4–5 RE during moderate substorm activity. This research suggests that at least a major class of the density structures that develop near 4 RE are tail-like in nature, joined to the main body of the plasmasphere. The apparent disagreement with Chappell's results from OGO 5, which are interpreted as showing regions of “detached” plasma beyond 5 RE, may be related to the pronounced spatial structure of electric fields observed in high-latitude ionospheric regions that are conjugate to the magnetospheric regions in which the OGO-5 observations were made.  相似文献   

19.
The effect of collisions on electrostatic instabilities driven by gravity and density gradients perpendicular to the ambient magnetic field is studied. Electron collisions tend to stabilize the short wavelength (ky?i ? 1, where ky is the perpendicular wavenumber of the instability and ?i is the ion Larmor radius) kinetic interchange mode. In the presence of weak ion-ion collisions, this mode gets converted into an unmagnetized ion interchange mode which has maximum growth rate one order smaller than that of the collisionless mode. On the other hand, electron collisions can excite a long wavelength resistive interchange mode in a wide wavenumber regime (10?3 ? ky ?i ? 0.3) with growth rates comparable to that of the collisional Rayleigh-Taylor mode. The results may be relevant to some of the spread F irregularities.  相似文献   

20.
Recent progress in modeling ionospheric current systems requires global conductivity models which can reflect substorm conditions on an instantaneous basis. For this purpose, empirical relations of the North-South component (ΔH) of the magnetic disturbance field observed at College with the Pedersen (Σp) and Hall (ΣH) conductivities deduced from the Chatanika radar data and their ratio (ΣHΣp) are examined. These empirical formulas allow us to construct approximate distribution patterns of Σp and Σ>H over the entire polar region on the basis of the distribution of ΔH at given instants by devising an appropriate weighting function for both the polar cap and the subauroral region. The global conductivity distributions thus obtained are compared with those employed by Kamide et al. (1981) and Spiro et al. (1982). The comparisons show that the gross features are similar among them. In addition, we also examine the relationship of ΔH with the North-South component of the electric field with the particle energy injection rate (uA) estimated from the Chatanika radar data. Based on the empirical relation between ΣH and uA the global distribution of the latter over the entire polar region at particular instants can also be obtained.  相似文献   

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