Cyclotron side-band emissions from ring-current electrons     

Kaichi Maeda 《Planetary and Space Science》1976,24(4):341-347

VLF-emissions with subharmonic cyclotron frequency from magnetospheric electrons have been detected by the S³-A satellite (Explorer 45) whose orbit is close to the magnetic equatorial plane where the wave-particle interaction is most efficient. These emissions are observed during the main phase of a geomagnetic storm in the nightside of the magnetosphere outside of the plasmasphere around L = 3–5. The emissions consist essentially of two frequency regimes, one below the equatorial electron gyro-frequency, , and the other above . The emissions below are whistler mode and there is a sharp band of “missing emissions” along . The emissions above are electrostatic mode and the frequency ranges up to . It is concluded that these emissions are generated by the enhanced relativity low energy (1–5 keV) ring current electrons, penetrating into the nightside magnetosphere during the main phase of a magneto storm. Although the high energy (50–350 keV) electrons showed remarkable changes of pitch angle distribution, their associations with VLF-emissions are not so significant as those of low energy electrons.  相似文献   

Deuteron whistler and trans-equatorial propagation of the ion cyclotron whistler     

S. Watanabe  T. Ondoh 《Planetary and Space Science》1976,24(4):359-364

New ion cyclotron whistlers which have the asymptotic frequency of one half the local proton gyrofrequency, $\text{G}{}_{\mathrm{p}}\text{2}$, and the minimum (or equatorial) proton gyrofrequency, G_pm, 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 G_pm or $\text{G}{}_{\mathrm{pm}}\text{2}$ are observed only in the region of $\text{B}{}_{\mathrm{m}}\text{>}\text{B}\text{2}$ or rarely $\text{B}{}_{\mathrm{m}}\text{>}\text{B}\text{4}$, where B is the local magnetic field and B_m 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 $\text{G}{}_{\mathrm{p}}\text{2}$ is the deuteron whistler, and that the ion cyclotron whistlers with the asymptotic frequency of G_pm or $\text{G}{}_{\mathrm{pm}}\text{2}$ are caused by the trans-equatorial propagation of the proton or deuteron whistler from the other hemisphere.  相似文献   

The relationship of the boundary layer of the magnetosphere to IPRP events     

K.D. Cole  R.J. Morris  E.T. Matveeva  V.A. Troitskaya  O.A. Pokhotelov 《Planetary and Space Science》1982,30(2):129-136

A model is proposed in which a mixture of hot solar wind and cold atmospheric plasma flowing in the dayside equatorial boundary layer towards the dawn-dusk plane generates hydromagnetic waves near the frequency $\text{ω = ω}{}_{\mathrm{Bi}}\text{¦1 ? T}{}_{\mathrm{\parallel }}\text{¦T}{}_{\mathrm{\perp }}\text{¦}$ where ω_Bi is the ion gyrofrequency and T_∥, T_⊥ are the temperatures of the solar wind plasma, parallel and perpendicular respectively to the magnetic field B. The model accounts for the properties of IPRP events, i.e. intervals of geomagnetic pulsations of periods rising on average from about 2 s to about 7 s over an interval of about 5 min. The diagnostic potential of this phenomenon for study of the boundary layer is indicated.  相似文献   

The role of protons of the radiation belts in the generation of Pc 3–5     

A.A. Kozhevnikov  A.B. Mikhailovsky  O.A. Pokhotelov 《Planetary and Space Science》1976,24(5):465-473

A new theory of the Alfvén wave generation in inhomogeneous finite β two component plasma is developed ($\text{β =}\text{8πρ}\text{β}{}_0{}^2$, ρ and B₀ are plasma pressure and unperturbed magnetic field, respectively). The analysis was carried out for these waves both for long wave approximation kρ_i ? 1 as well as for $\text{kρ}{}_{\mathrm{i}}\text{? 1}$ (k and ρ_i are wave vector and larmor radius of protons). The influence of the loss-cone on the development of the instability is considered. The theory is applied to explain the generation mechanism of Pc 3–5.  相似文献   

Control of impulsive penetration of solar wind irregularities into the magnetosphere by the interplanetary magnetic field direction     

J. Lemaire  M.J. Rycroft  M. Roth 《Planetary and Space Science》1979,27(1):47-57

Impulsive penetration of a solar wind filament into the magnetosphere is possible when the plasma element has an excess momentum density with respect to the background medium. This first condition is satisfied when the density is larger inside than outside the plasma inhomogeneity. In this paper we discuss the second condition which must be satisfied for such a plasma element to be captured by the magnetosphere: the magnetization vector (M) carried by this plasma must have a positive component along the direction of B₀, the magnetic field where the element penetrates through the magnetopause. On the contrary, when $\text{M · B}{}_0\text{< 0}$, the filament is stopped at the surface of the magnetopause. Thus the outcome of the interaction of the filament with the magnetosphere depends upon the orientation of the Interplanetary Magnetic Field. For instance, penetration and capture in the frontside magnetosphere implies that B_sw, the Interplanetary Magnetic Field, has a southward, or a small northward, component. Penetration and capture in the northern lobe of the magnetotail is favoured for an IMF pointing away from the Sun; in the southern lobe B_sw must be directed towards the Sun for capture. Finally, for capture in the vicinity of the polar cusps the magnetospheric field (B₀) assumes a wider range of orientations. Therefore, near the neutral points, it is easier to find a place where the condition $\text{M · B}{}_0\text{> 0}$ is satisfied than elsewhere. As a consequence, the penetration and capture of solar wind irregularities in the cleft regions is possible for almost any orientation of the interplanetary magnetic field direction. All observations made to date support these theoretical conclusions.  相似文献   

Total current to cylindrical collectors in collisionless plasma flow     

R. Godd  J.G. Laframboise 《Planetary and Space Science》1983,31(3):275-283

A theory is presented for charged-particle collection by a cylindrical conducting object, such as a spacecraft or an electrostatic probe, which is moving transversely through a collisionless plasma, such as those in the upper atmosphere and space. The calculation is approximate, using symmetric potential profiles which are exact for the infinite-cylinder stationary case. Theoretical current predictions are presented for ratios of collector potential to electron thermal energy eφ_c/kT_e from 0 to ?25, for ion-to-electron temperature ratios T_i/T_c = 1 and 0.5, ratio of collector radius to electron Debye length r_c/λ_D from 0 to 100, and ratio of flow speed to ion thermal speed $\text{S}{}_{\mathrm{i}}\text{= U/(2kT}{}_{\mathrm{i}}\text{/m}{}_{\mathrm{i}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)}$ from 0 to 10. Comparisons with existing exact calculations by other authors show that none of these fulfil all of the requirements for nontrivial comparison. Appropriate parameter ranges for future exact calculations are thereby suggested. These are as follows: (a) r_c/λ_D should be large enough that the collector not be in or near orbit-limited conditions; (b) the ratio $\text{S}{}_{\mathrm{i}}{}^2\text{/¦χ}{}_{\mathrm{c,\; i}}\text{¦}$ of ion directed energy to potential energy change in the sheath, should be close to unity or if .  相似文献   

An estimator of the underlying size distribution of overlapping impact-craters     

W.W. Mullins 《Icarus》1976,29(1):113-123

The stochastic model of lunar type impact-crater formation which assumes (a) random impacts, (b) circular craters, each obliterating any portions of earlier craters lying within, and (c) a probability P_i(t) that a newly formed crater (primary or secondary) has an area a_i is analyzed to develop a method of estimating P_i from the final overlapping pattern. It is found that if each crater is weighted by the fraction of the rim which is visible and which lies in an observation area A, then the expected value of the weighted sum $\text{Ω}{}_{\mathrm{i}}$ of craters of area a_i is simply proportional to P_i for any degree of coverage under several conditions, including (a) constant P_i for all i, and (b) P_i stepping from a constant early value to zero (for some i's) with otherwise arbitrary bombardment. Furthermore, in the general case, the expected value of the contribution $\text{ΔΩ}{}_{\mathrm{i}}\text{(t}{}_0\text{)}\text{to}\text{Ω}{}_{\mathrm{i}}$ produced during t₀ ± Δt/2 is found to be proportional to P_i(t₀). Thus measurement of $\text{Ω}{}_{\mathrm{i}}$ in the first two cases, or of $\text{ΔΩ}{}_{\mathrm{i}}$ if crater age data is available in the last case, provides an estimate of the desired P_i. Therefore the $\text{Ω}{}_{\mathrm{i}}$ introduce the correct weighting factors that just compensate for the effect of overlap.Expressions for the variances of $\text{Ω}{}_{\mathrm{i}}\text{and}\text{Ω = Σ}{}_{\mathrm{i}}\text{Ω}{}_{\mathrm{i}}$ are derived from which it is shown that under the above conditions, $\text{Ω}{}_{\mathrm{i}}\text{/Ω}\text{or}\text{ΔΩ}{}_{\mathrm{i}}\text{/ΔΩ}$ are consistent estimators of P_i. Formal evaluation of the variances is carried out in the special case of constant P_i and no secondary cratering. A criterion for the degree of coverage is given; in particular it is shown that the expectation of $\text{σ = Σ}{}_{\mathrm{i}}\text{a}{}_{\mathrm{i}}\text{Ω}{}_{\mathrm{i}}$ at saturation is just A.  相似文献   

Mass-discrimination in ion and neutral extraction by mass-spectrometers under spacecraft conditions     

Jen-Shih Chang  R. Godard  J.G. Laframboise 《Planetary and Space Science》1979,27(10):1213-1220

  相似文献   

Low-frequency upstream wave as a probable source of low-latitude Pc 3–4 magnetic pulsations     

Kiyohumi Yumoto 《Planetary and Space Science》1985,33(2):239-249

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 θ_XB of the IMF observed at ISEE 3. Moreover, the Pc 3–4 frequencies ($\text{?}$) 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(B_IMF).The correlation of $\text{?}$ of the compressional Pc 3–4 waves at GOES 2 against B_IMF 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 ($\text{σ}{}_{\mathrm{n}}\text{= ± Δ?}\text{mHz}$) of the observed frequencies from the form $\text{?}$ (mHz) = 6.0 × B_IMF (nT) is larger at the ground stations than at GOES 2, i.e., $\text{Δ? = ± 6.6}\text{mHz at}$GOES 2, and ±(13.9, 9.1, 10.7, 12.1) mHz at (COL, SGC, EWA, ONW), respectively. The correlations between the IMF magnitude B_IMF 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 $\text{?}$ against the IMF magnitude B_IMF for the compressional Pc 3–4 waves at GOES 2 are restricted within the forms $\text{? = 4.5 × B}{}_{\mathrm{<mtext>IMF</mtext>}}\text{and}\text{? = 7.5 × B}{}_{\mathrm{<mtext>IMF</mtext>}}$. The frequency distribution is in excellent agreement with the speculation ($\text{<ω}{}_{\mathrm{sc}}\text{Ω}{}_{\mathrm{i}}\text{= 0.3 ～ 0.5}$) 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   

Analysis of HI content in galaxies     

《Chinese Astronomy and Astrophysics》1981,5(2):205-211

We have collected data on 241 galaxies from 13 sources and made a statistical analysis after reduction to a uniform system. We found that the Hubble sequence is one of increasing $\text{〈}\text{M}{}_{\mathrm{<mtext>H</mtext>}}\text{M}{}_{\mathrm{<mtext>T</mtext>}}\text{〉}$ and $\text{〈}\text{M}{}_{\mathrm{<mtext>H</mtext>}}\text{L}{}_{\mathrm{<mtext>B</mtext>}}\text{〉}$, these mean values increasing monotonically from .0016 and .024 at E to .084 and .83 at Im, but the dispersion is large.The HI content in barred spiral is greater than that in ordinary spirals, and this is consistent with their statistics of angular momentum and colour.The HI content is related to colour; it is greater in bluer systems. The large dispersion suggests that it also depends on some other factors, but these are smoothed out when averaged over each type, resulting in a linear relation between $\text{〈log(}\text{M}{}_{\mathrm{<mtext>M</mtext>}}\text{M}{}_{\mathrm{<mtext>T</mtext>}}\text{〉}$ and 〈(B ? V^O_T)〉. Unlike the colour-colour diagram, the large dispersion on the $\text{log}\text{(}\text{M}{}_{\mathrm{<mtext>H</mtext>}}\text{L}{}_{\mathrm{<mtext>B</mtext>}}\text{) ? (B ? V}{}^0{}_{\mathrm{<mtext>T</mtext>}}\text{)}$ is not related to peculiar galaxies.  相似文献   

New high-speed photometry of EH Lib and a binary interpretation of its period change     

《Chinese Astronomy and Astrophysics》1982,6(1):24-27

Six times of maxima of the ultrashort-period cepheid variable EH Librae were measured in 1980 May to June and in 1981 January, with a three-channel photocounting high-speed photoelectric photometer. These, together with all the photoelectric times of maxima over the past 30 years, are used to re-examine the nature of the change of the period. We found that we can fix the times of maxima by the following formula where T₀ = HJD 2433438.6088 and P₀ = 0.0884132445 d represent the initial maximum epoch and the pulsation period, β = ?2.8 × 10^?8/yr; A = 0.0015 d, P₀ = 6251 d = 17.1 yr are the semi-amplitude and the period of the sine curve, and E is the number of periods elapsed since T₀, and (E₀ = 70700).If we interpret this 17.1 year periodicity as a modulation of the phase of maximum by binary motion, then the semi-amplitude of the orbital radial velocity variation is K = 2πasini/E₀ = 0.45 km/s and the mass function is   相似文献   

Excitation of magnetosonic waves with discrete spectrum in the equatorial vicinity of the plasmapause     

A.V. Gul&#x;elmi  B.I. Klaine  A.S. Potapov 《Planetary and Space Science》1975,23(2):279-286

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 = sω_p can be excited by energetic protons, with non-monotonic dependence on transverse energy ($\text{??/?ε}{}_{\mathrm{\perp }}\text{> 0}$). 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   

VLF-emissions associated with ring current electrons: Off-equatorial observations     

Kaichi Maeda  Paul H. Smith 《Planetary and Space Science》1981,29(8):825-835

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 $\text{f}{}_{\mathrm{<mtext>Ho</mtext>}}\text{2}$ and that the intensities of the off-equatorial emission above $\text{f}{}_{\mathrm{<mtext>Ho</mtext>}}\text{2}$ are very weak in contrast to those of the near equatorial emissions, where $\text{f}{}_{\mathrm{<mtext>Ho</mtext>}}\text{2}$ is the equatorial electron gyrofrequency corresponding to the local gyrofrequency f_H 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 $\text{f}{}_{\mathrm{<mtext>Ho</mtext>}}\text{2}$ 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   

Empirical model of the E-region electron temperature around noon and at low magnetic activity     

S. Duhau  M.C. Azpiazu 《Planetary and Space Science》1985,33(8):909-914

Electron temperature measurements made with Langmuir probes at E-region heights together with deviative absorption data show that the electrons are not in thermal equilibrium with the neutrals. Moreover, for very quiet days (A_p ? 7, K_p ? 1⁺ throughout the whole day) and hours close to noon the quotients between the electron and neutral gas temperature profiles have a similar behaviour. In this paper T_e profiles measured in situ with Langmuir probes and T_n, profiles given by neutral atmosphere models, both in the specified ionospheric conditions, are used to compute $\text{T}{}_{\mathrm{e}}\text{T}{}_{\mathrm{n}}$ profiles. Each of the profiles thus obtained is fitted by a Lorentzian curve and the variation with F_10.7 of its parameters is also fitted by simple mathematical expressions.  相似文献   

Interactions of plasmas with magnetic field boundaries     

A.D.R. Phelps 《Planetary and Space Science》1973,21(9):1497-1509

The magnetopause, the boundary layer, or current sheath, which separates the magnetosphere from the solar wind, is the particular interaction considered in this paper.The collision free electron skin depth, $\text{ξ}{}_{\mathrm{e}}\text{=}\text{c}\text{ω}{}_{\mathrm{pe}}$, where c is the velocity of light and ω_pe, is the plasma frequency, gives a classical measure of the penetration depth of a collisionless plasma by an electromagnetic field. This penetration depth is small compared with the dimensions of the magnetosphere and hence the boundary layer may be conveniently considered in one dimension.In General all one dimensional solutions lie within an order of magnitude of the value of ξ_e, the only exception being the important one, in which the electric field perpendicular to the current sheath plane is not present, either due to a particular trapped particle distribution or due to a short circuiting end effect. For this exception the thickness is increased by the factor ($\text{m}{}_{\mathrm{i}}\text{i/m}{}_{\mathrm{e}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$.The current sheath solutions discussed are equilibrium solutions but not necessarily stable equilibrium solutions.The extension of the models to three dimensions has a larger effect than might at first be expected. The effect may be intuitively understood as a consequence of flux conservation in the sheath. The one dimensional solutions then correspond to the current sheath profiles at the thinnest point of the three dimensional sheath.  相似文献   

On fourier-analysis of geomagnetic pulsations pc-1, “two-fold” and “three-fold” pulsations pc-1 and fundamental frequencies of the magnetospheric cavity—I     

Ya.L. Alpert  D.S. Fligel 《Planetary and Space Science》1985,33(9):993-1012

The paper gives the results of detailed studies of the frequency spectra $\text{S}{}_{\mathrm{s}}\text{(?)}$ of the chain of the wave packets F_s(t) of geomagnetic pulsations PC-1 recorded at the Novolazarevskaya station. The bulk of the energy of F_s(t) is concentrated in the vicinity of the central frequencies $\text{?}{}_{\mathrm{s0}}$ of spectra—the carrier frequencies of the signals. The velocity $\text{V}{}_0\text{≌ 6.10}{}^3\text{km s}{}^{\mathrm{?1}}$ 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 $\text{? = 2?}{}_{\mathrm{s0}}\text{and}\text{3?}{}_{\mathrm{s0}}$ 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 $\text{?}{}^{\mathrm{\pm }}{}_{\mathrm{sK}}$. Frequency differences $\text{Δ?}{}_{\mathrm{sK}}{}^{\mathrm{\pm }}\text{=}\text{¦?}{}_{\mathrm{s0}}\text{? ?}{}_{\mathrm{sK}}{}^{\mathrm{\pm }}\text{¦}\text{= (0.011,0.022}\text{and}\text{0.035)}\text{Hz}$ 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   

Determination of magnetic field direction in a comet's head     

D.A. Varshalovich  G.F. Chörny 《Icarus》1980,43(3):385-390

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 $\text{I(D}{}_2\text{)}\text{I(D}{}_1\text{)}$ changes within ±5%, and the polarization degree P(D₂) within ±25%. Measurements of $\text{I(D}{}_2\text{)}\text{I(D}{}_1\text{)}$ 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   

Characteristics of localized resonance coupling oscillations of the slow magnetosonic wave in a non-uniform plasma     

Kiyohumi Yumoto 《Planetary and Space Science》1985,33(9):1029-1036

We analyze linear resonance oscillations in a non-uniform one-fluid finite-β plasma, which is oversimplified to understand easily fundamental characteristics of the resonance oscillations. A linear resonance oscillation of localized slow magnetosonic mode $\text{[ω}{}^2{}_{\mathrm{s}}\text{=}\text{ω}{}^2{}_{\mathrm{A}}\text{(1 +}\text{V}{}^2{}_{\mathrm{A}}\text{V}{}^2{}_{\mathrm{s}}\text{)}\text{]}$, which has the diamagnetic property in a uniform plasma, is newly found to be excited in the radially non-uniform plasma. The localized slow resonance indicates a radially polarized compressional oscillation (δB_∥ ? δB_H ? δB_D). The sense of the Alfvénic polarizations in the H-D plane near the resonant point is a function of both the propagation in the azimuthal direction and the slope of wave amplitude in the radial direction, whereas the sense of the resonant slow magnetosonic polarizations changes in accordance only with the switch in the azimuthal propagation direction. Further multi-satellite studies are necessary to establish the resonant structures of the slow magnetosonic waves in the magnetosphere.  相似文献   

Magnetospheric chorus: Occurrence patterns and normalized frequency     

W.J. Burtis  R.A. Helliwell 《Planetary and Space Science》1976,24(11):1007-1024

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 $\text{4? L? 10}$. 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 $\text{?}{}_{\mathrm{H}}$, the normalized frequency distribution of chorus observed within 10° of the dipole equator shows two peaks, at $\text{?}\text{?}{}_{\mathrm{H}}\text{? 0.53}$ and $\text{?}\text{?}{}_{\mathrm{H}}\text{? 0.34}$. This bimodal distribution is a persistent statistical feature of near equatorial chorus, independent of L, LT and K_p. 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 $\text{?}\text{?}{}_{\mathrm{H}}\text{= 0.50}$. When two bands are simultaneously present individual emission elements only rarely show one-to-one correlation between bands. For low K_p the median bandwidth of the upper band, gap and lower band are all ～16% of their centre frequencies, independent of L; for higher K_p 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 K_p 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, $\text{?}\text{?}{}_{\mathrm{H}}\text{? 0.5}$, 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   

A possible mechanism of formation of faculae     

Ni Xiang-bin  Jiang Yao-tiao  Chen Zai-zhang  Fang Cheng 《Chinese Astronomy and Astrophysics》1985,9(4):273-277

We propose a new heating mechanism of faculae. We think that the formation of faculae is a result of the Joule dissipation of the Hall current generated by the interaction of the convection field of granules in an active region and the inter-granular magnetic field. For a region to generate effectively Hall current, its characteristic length must be such that the magnetic Reynolds number is less than 1. The equation of energy balance in the facula region is .For five observational models of faculae, we calculated the corresponding velocity fields, and the results are in basic agreement with the observed fields. The present mechanism explains the dependence of the facula brightness on the magnetic and velocity fields, the apparent distribution of the faculae on the solar disk and suggest a possible interpretation of the five structures of faculae.  相似文献