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1.
A generation mechanism for 1–30 Hz waves of the second category, observed near the plasmapause by Taylor and Lyons (1976), is suggested in terms of a resonant electron instability. The instability arises because of the resonant interaction between the ring current electrons outside the plasmapause and the ordinary mode drift waves. The instability can generate waves in the frequency range from 0.45 to 35.0 Hz in the region between L = 4.5 and 5.5. The instability can also explain satisfactorily the other properties such as no changes in the proton distributions, the direction of the wave magnetic field and the localization of the region of wave activity, associated with these waves.  相似文献   

2.
Electromagnetic waves propagating transverse to the magnetic field, containing inhomogenous and loss cone plasma, may become unstable due to the excitation of resonant proton, resonant electron and drift cyclotron instabilities. Resonant proton instability gets excited in inhomogenous plasma, irrespective of the presence of temperature anisotropy, loss cone or temperature gradient. However, the growth rate of this instability is much smaller than the other two instabilities. The maximum growth rates of resonant electron instability are enhanced with the increase of loss cone index, gradients in transverse temperature and magnetic field, and with the decrease of temperature anisotropy and gradients in density and parallel temperature. The drift cyclotron instability exists in a bounded range of wave numbers and its growth rate increases with the increase of electron temperature, density and magnetic field gradient, and with the decrease of proton temperature and temperature anisotropy. In the region of ring current for beyond plasmapause the resonant proton and resonant electron instabilities have the characterstic frequencies around 0.1Ωp and growth rates ~10?6Ωp and 10?3Ωp, respectively. In the ring current region the drift cyclotron instability is not excited whereas in the plasma sheet region the frequency and growth rate of this instability are around Ωp and 10?2Ωp, respectively. These instabilities can accelerate the ring current particles along the magnetic field lines and dump them into the auroral region.  相似文献   

3.
Waves with frequencies near the harmonics of the proton-cyclotron frequency, and propagating almost transverse to the ambient magnetic field, can become unstable by hot protons having an anti-loss cone (ALC) distribution function. The maximum growth rates increase with an increase in anti-loss cone index, ratio of the temperatures of trapped to missing protons, and with a decrease in H ( H being the ratio of transverse thermal pressure of protons to magnetic field pressure). The growth rates are typically in the range 0.01–1.0 , where is the proton-cyclotron frequency. This instability may be relevant to the observations of EHC waves on auroral field lines (Kintner, 1979), ULF waves in the day-side magnetosphere (Perrautet al., 1978) and the lowfrequency part of the electric field spectrum (from 5 Hz to 20 Hz) in the region upstream of the bow-shock (Gurnettet al., 1979).  相似文献   

4.
The particle energy required to generate the observed VLF hiss in the Jovian magnetosphere has been computed under longitudinal and transverse resonance condition. It is shown that the minimum energy required by electrons to generate VLF hiss under the longitudinal resonance condition lies in the range of 100eV–1keV for the wave frequencies of 2–10 kHz, while the corresponding energy range for the transverse resonance condition for the same frequency range comes out to be 8 keV–40 keV. Further, the average radiated power by the erenkov process in the Jupiter's magnetosphere atL=5.6 Rj by electrons of energy 10 eV, 100 eV, and 1 keV for the wave frequency of 5 kHz has also been computed.  相似文献   

5.
Measurements of charged particle fluxes at energies >-13 MeV (if protons), by means of a detector system of high geometrical factor (950 cm2 sr), flown on OGO-6 satellite, reveals a ring of low energy charged particles around equator with fluxes of the order of 50–70 particles (m–2 s–1 sr–1), in the altitude range of 400–1100 km. The ring of charged particles exists below the inner radiation belt and is restricted to ±4° of the geomagnetic equator. Distribution of the maximum flux with geomagnetic latitude andL is presented. Comparison of the observed fluxes with earlier measurements of low energy particles, reveals a differential energy spectrum of the type KE– with the exponent nearly equal to 2.4 to 3.  相似文献   

6.
The electromagnetic ion cyclotron instability is shown to be nonconvective for a wide range of plasma β's and ring current proton anisotropies A. The addition of cold plasma to the ring current enlarges the region of the β-A parameter space for nonconvective instability. Thus, despite the high Alfvén speed outside the plasmasphere, ion cyclotron wave amplitudes could grow to appreciable levels and contribute to the pitch-angle and energy diffusion of ring current protons.  相似文献   

7.
Equatorial charge-exchange lifetimes of ring current protons are recalculated, and the decay of a collection of ring current protons trapped on an L-shell by the charge-exchange mechanism is determined using recent models of the hydrogen geocorona. Observational results pertaining to the decay of ring current energy are briefly discussed, as are a number of competing loss mechanisms. Since charge exchange is a simple physical process which is very efficient in removing ring current energy from L-shells near to the Earth (say, L < 4), it is suggested that it may well be the dominant loss mechanism in this region.  相似文献   

8.
The velocity shear of ion beams observed in the polar cusp region can drive the kinetic Alfvén modes unstable. A hot ion beam can excite both a resonant kinetic Alfvén wave instability and a nonresonant coupled Alfvén ion-acoustic wave instability. For the case of a cold ion beam only the latter instability is excited. For the altitude range of 5–7R e , velocity shearS0.04–1.0 is needed to excite the kinetic Alfvén wave instabilities. HereS=(dV B / cB dx), whereV b is the streaming velocity,and cB is the gyrofrequency of the bean ions. The excited modes have frequencies, in the satellite frame of reference, in the ULF frequency range. The noise generated by the velocity shear-driven Alfvén modes is electromagnetic in nature. These modes have a substantial component of parallel electric fields and, therefore, they can play an important role in the ionosphere-magnetosphere coupling process occurring in the polar cusp region.  相似文献   

9.
The precipitation patterns of 6 keV protons at 10° and 80° pitch angles have been mapped at altitudes <1500 km from the ESRO 1A and 1B spacecraft. Equatorward of the trapping boundary, a region of isotropic precipitation, bounded on its equatorward border by a region of anisotropic (depleted loss cone) precipitation, is always observed. The latitudinal location of this transition appears to be nearly spatially coincident with the plasmapause. Similar precipitation patterns are shown to exist for higher energy protons. The general absence of enhanced precipitation at the plasmapause suggests that the inner boundary of the ring current is not usually produced by an enhanced proton pitch angle diffusion process. The isotropic precipitation observed beyond the plasmapause is most consistent with the occurence of an electrostatic instability throughout the ring current zone. It is doubtful whether the proposed cold Li plasma seeding experiments beyond the plasmapause could significantly increase the observed natural proton precipitation rates.  相似文献   

10.
The waves, propagating nearly transverse to the ambient magnetic field, with frequencies near the harmonics of the proton-cyclotron frequency are studied in an inhomogeneous plasma with protons having loss-cone distributions. Three types of drift cyclotron instabilities have been studied: (i) non-flute instability; (ii) B-resonant instability; and (iii) non-resonant instability. Increases of loss-cone and density gradient increase the growth rates of all three instabilities. Increases in the positive temperature gradient and t (ratio of thermal pressure of trapped protons to magnetic field pressure) have a stabilizing effect on the non-flute and non-resonant instabilities and a destabilizing effect on the B-resonant instability. The non-resonant instability has an interesting feature: a particular harmonic can be excited in two separate bands of unstable wave numbers. These instabilities can play an important role in the dynamics of the ring current and the inner edge of the plasma sheet region of the magnetosphere. The discrete turbulence generated by them would give rise to precipitation of protons on the auroral field lines, which may contribute to the excitation of diffuse aurora. These instabilities may be relevant to the observation of harmonic waves at 6R E by Perrautet al. (1978).  相似文献   

11.
The velocity gradients of the contrastreaming electron beams observed in the Earth's magnetosphere can excite three types of ordinary mode instabilities, namely (i) B-resonance electron instability, (ii) ion cyclotron instability, and (iii) unmagnetized ion instability. The B-resonance electron instability occurs at small values of the shear parameter 10–4<S<10–3, whereS = [(1/e){dU o(x)}/(dx)] (U 0(x) and e being the streaming velocity of the electron beams and the electron cyclotron frequency, respectively). Near the equatorial plane of the bouncing electron beams region, this instability can generate electromagnetic waves having frequenciesf(0.045–0.2) Hz and wavelentghs (0.5–10)km, and the wave magnetic field is polarised in a radial direction. This instability can also occur in the plasma sheet region during the earthwards and tailwards plasma flows events and can generate waves, with wave magnetic field polarised along north-south direction, in the frequency rangef(0.007–0.02) Hz with (10–100)km nearR=–35R E . For 10–3<S<10–2, the ion cyclotron instability is excited and it can generate waves up to 5th harmonic or so of ion cyclotron frequency. ForS>10–2, the unmagnetized ion instability is excited which can generate electromagnetic waves having frequences from 5 to 50 Hz and typical wavelengths (0.5–6)km. The growth rates of all the three velocity shear driven instabilities are reduced in the presence of cold background plasma. The turbulence generated by these instabilities may give rise to enhanced effective electron-electron and electron-ion collisions and broaden the bouncing electron beams.  相似文献   

12.
Various aspects of Etchetoet al.'s theory are studied in detail. It is shown that the inequalitya <b <c fails at lowL shells. A comparative study of wave spectral densities generated during weak/strong diffusion events suggests that this theory is strictly not applicable at lowL shells. It is found that different criterea for measuring the diffusion of energetic electrons by ELF waves (100–3000 Hz) contradict each other. If one region is strong diffusion region for one criteria, it may be a weak diffusion region according to another criteria. It is found that whereas critical wave intensities (1–2 pT2/Hz) can cause strong diffusion of energetic electrons, if one applies Fokker—Planck's diffusion approach, very large wave intensities are needed for strong diffusion if we apply Etchetoet al.'s approach.  相似文献   

13.
The cometary images taken on 1986 January 8.590 and 8.638 UT (R-0.9 AU, ~ 1.29 AU) at Gurushikhar, Mt. Abu, India (24 °39 N, 72 °43 E alt: 1700 m) show distinct condensation region in the tail direction. The size of the condensation region is 4 × 103 km. The condensation region showed up strongly in the blue emission, implying the abundance of CO+. It was inferred to be moving with a velocity of 37 ± 3 km/s relative to the comet at a distance of 2.3 × 105 km from the nucleus in the tailward direction.The analysis show that the condensation was a result of rapid ionization mechanism, with a time scale of \~103 to 104 sec. The most probable mechanism for producing the ionization region was found to be the discharge of cross tail electric current passing through the neutral sheet in the near nucleus region followed by an outburst observed in IR wavelengths at 8.1 UT. It was accelerated by J × B drift at a rate of ~24 cm/sec2 to the position observed by us.This feature, most probably is the precursor of the first dramatic Disconnection Event (DE) observed in Halley's Comet at Jan.10.375 UT. This supports the conjecture that the tail features originate in the coma with a velocity of ~20–40 km/s.  相似文献   

14.
Whistlers recorded at low latitude ground stations of Gulmarg, Nainital and Varanasi were used to infer the east-west component of electric field on the nightside plasmasphere atL=1.2, 1.12, and 1.07 during magnetic storm periods. The method of measuring electric field from the observed cross-L motions of whistler ducts within the plasma-sphere, indicated by changes in nose frequency of whistlers has been outlined. The nose frequencies of the non-nose whistlers under consideration have been deduced from Dowden-Allocock linear Q-technique. The results show eastward electric fields of 0.7 mVm–1 in the equatorial plane of Gulmarg and 0.3 mVm–1 in the equatorial plane of Nainital in the premidnight local time sector. Near midnight, there is a sharp transition from eastward field to a westward electric field of 0.2–0.7 mV m–1 for Gulmarg, 0.3–0.5 mV m–1 for Nainital and 0.1–0.3 mVm–1 for Varanasi.  相似文献   

15.
BUSS observations of the profiles of two well observed spectral lines in the ultraviolet spectrum of CMi (Procyon; F5 IV–V) are analysed with a Fourier transform method in order to determine values of various parameters of the velocity field of the upper photosphere. We find a microturbulent line-of-sight velocity componentL = 0.9 ± 0.4 km s–1, a macroturbulent velocity componentL M = 5.3 ± 0.2 km s–1, and a rotational velocity componentv R sini=10.0±1.2 km s–1. In these calculations a single-moded sinusoidal isotropic macroturbulent velocity function was assumed. The result appears to be sensitive to the assumed shape of the macroturbulence function: for an assumed Gaussian shape the observations can be described withv R sini=4 km s–1 andL M = 11.6 ± 2.7 km s–1. A comparison is made with other results and theoretical predictions.  相似文献   

16.
Secondary explosions of the primary ice fragments ejected in the explosion of the electrolyzed massive ice envelopes of the Galilean satellites are capable of imparting velocities of up to ~5km s–1 to the secondary fragments. As a result, the secondary fragments can enter the orbits of the irregular satellites (Agafonova and Drobyshevski, 1984b) and the Trojan libration orbits. In the latter case a perturbation velocity of V 0.3–2 km s–1 is sufficient.The primary fragments ejected by the gravitational perturbations due to the Galilean satellites sunward from Jupiter's sphere of action move faster relative to the Sun than Jupiter does and therefore reach their first aphelion ahead of Jupiter in the neighborhood of L 4. At the same time the fragments propelled from Jupiter's sphere of action beyond the planet's orbit approach it again in their perihelia behind Jupiter in the region of L 5. The concentration of the fragments and, hence, the frequency of their collisions and explosions at L 4 turn out to be much greater than those at L 5. As a result, the number of the secondary fragments of diameter 15 km captured into libration orbits ahead of Jupiter can be as high as many hundreds and should exceed by more than a factor 3.5 that captured behind Jupiter.Since the icy mix of the fragments contains hydrocarbons and particulate material (silicates and the like), after ice sublimation from the surface layers the Trojans should reveal type C and RD spectra typical for Jupiter's irregular satellites, comet nuclei and other distant ice bodies of similar origin. Among the Trojans there cannot be rocky or metallic objects which are known to exist in the main asteroid belt.It is shown that a velocity perturbation of 150–200 m s–1 resulting from a purely mechanical impact of two bodies may be sufficient to move collision fragments from the orbits of the Trojans to horseshoe-shaped trajectories with a subsequent transfer to the cometary orbits of Jupiter's family.  相似文献   

17.
Kobanov  N.I.  Makarchik  D.V.  Sklyar  A.A. 《Solar physics》2003,217(1):53-67
In this paper we carry out an analysis of the spatial–temporal line-of-sight velocity variations measured in the chromospheric (H, H) and photospheric (Fei 6569 Å, Fei 4864 Å, Nii 4857 Å) lines at the base of 17 coronal holes. Time series of a duration from 43 to 120 min were recorded with the CCD line-array and the CCD matrix. Rather frequently we observed quasi-stationary upward flows with a measured velocity of up to 1 km s–1 in the photosphere and up to 4–5 km s–1 in the chromosphere (equivalent radial velocity of up to 3 km s–1 and up to 12–15 km s–1 accordingly) near dark points on the chromospheric network boundary inside polar CH. Line-of-sight velocity fluctuation spectra contain meaningful maxima in the low-frequency region clustering around the values 0.4, 0.75, and 1 mHz. Usually, the spatial localization of these maxima mutually coincides and, in our opinion, coincides with the chromospheric network boundary. Acoustic 3- and 5-min oscillations are enhanced in the coronal hole region and reach 1 km s–1 in the photosphere and 3–4 km s–1 in the chromosphere. These oscillations are not localized spatially and are distinguished throughout the entire region observed.  相似文献   

18.
The pick up cometary ion distributions are shown to excite Alfvénic mode instabilities, slow ion-acoustic mode instability and a lower hybrid instability during solar wind-comet interaction. The growth rates of all these instabilities become larger as the comet is approached. The lower hybrid instability is shown to account for the low-frequency 0–300 Hz electrostatic turbulence observed near comet Halley. The Alfvén modes can grow to large amplitudes and become modulationally unstable, in the presence of low-frequency density fluctuations, going over to envelope Alfvén solitons. A model consisting of a gas of Alfvén solitons is suggested to explain the hydromagnetic turbulence observed near comet Halley and comet Giacobini-Zinner.  相似文献   

19.
The brightness distribution of diffuse soft X-rays in the pulse height range 0.15–0.3 keV (L-band) and 0.5–0.8 keV (M-band) are obtained over a quarter of the sky centered at the galactic anticenter with 1.5 m polypropylene window proportional counters on board a sounding rocket. In theL-band three enhanced regions are noticed on the map. They coincide with the northern and southern Hi holes and the inner part of the galactic radio Loop II.In the northern Hi hole theN H dependence of theL-band flux and the hardness ratioM/L can be fitted with a local hot plasma model with the absorption by a low velocity neutral hydrogen gas (|V|<25 km s–1) along the line of sight. The X-ray feature of Loop II is similar to that of Loop I. In the lowN H region (<3×1020 H atoms cm–2) theM/L value is lower than 0.3, whereas it varies in the range 0.1–0.4 at low latitudes (|b|<300). This fact seems to be interpreted in terms of a model that a number of hot plasma clouds contribute to X-ray emission.  相似文献   

20.
The degree of convective instability as expressed by the growth rate of linear modes, is calculated for a plane parallel polytropic atmosphere in the presence of radiative damping, without using Boussinesq approximation. A comparison with the results based on the Boussinesq approximation reveals that the use of the Boussinesq approximation leads to an overestimation of the radiative damping. The computation of as a function of the horizontal wave number yields a wavelength of maximal instability under a variety of conditions. For reasonable choices of physical parameters appropriate to the solar atmosphere, the fastest growing wavelengths turn out to be in the range 600–1200 km, and their e-folding times are in the range 200–2000 s.NAS-NRC Senior Research Associate on leave of absence from the Tate Institute of Fundamental Research, Bombay.  相似文献   

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