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1.
During the flight of a Petrel rocket, instrumented by the SRC Radio and Space Research Station with Geiger counters and launched westwards from South Uist, Outer Hebrides, Scotland (L=3.38), a transient increase was observed in the intensity of energetic electrons having pitch angles between 60 and 120°. The increase, by a factor of 20 above the quasi-steady intensity observed throughout the remainder of the flight, occurred in 0.8 sec and was simultaneous for both >45 keV and >110 keV electrons. Recorded ～0.5 sec later, on the ground, was a two-hop whistler. During the enhanced electron intensity event, the entire duration of which was ～6 sec, the four-, six- and eight-hop whistlers were also received. From an analysis of the whistlers' spectrogram, it is concluded that the whistlers were ducted through the magnetosphere along the L=3.3 ±0.1 field line; the electron density in the equatorial plane is found to be 330 ±10 cm?3, a value characteristic of conditions within the plasmapause. It is suggested that these temporally and/or spatially associated phenomena, rather than arising by a chance coincidence, were the result of a gyroresonant interaction between energetic electrons and whistler mode waves moving in opposite directions. For gyroresonance on this field line at the equator, the parallel component of energy of the electrons is 25 keV at 3 kHz in the whistler band, or 100 keV at 1 kHz below it. It is suggested that a magnetospheric event occurred, causing both sudden enhanced electron precipitation and favourable conditions for the propagation and/or amplification of whistlers. A possible explanation is that energetic electrons, having a sufficiently anisotropic distribution function and associated with those injected during an earlier auroral substorm, become unstable via the transverse resonance instability when they drift into the plasmasphere, a region of high density thermal plasma.  相似文献   

2.
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   

3.
The convection electric field in the vicinity of the plasmapause in the midnight sector during magnetospheric substorms has been obtained on the basis of spectral analysis of Pc1 hydromagnetic (HM) waves observed at the low latitude station, Onagawa (Φ = 28.°3, Λ = 206.°8). Variations of the field are consistent for four independent substorm events studied. The calculation implies that the convection electric field increases westwards up to ~1.0 mV/m during the expansion phase of the substorms, changes polarity near the end of the expansion phase, and then points eastwards during the recovery phase.  相似文献   

4.
Ilan Roth   《Planetary and Space Science》2007,55(15):2319-2323
Direct observations or deduced analysis indicate clearly that formation of intense fluxes of relativistic electrons is an important ingredient in the evolution of numerous active magnetized plasma systems. Examples of relativistic electron energization include the recovery phase of a planetary magnetic storm, post solar flare coronal activity and the afterglow of gamma ray bursts. It is suggested that there exists a universal mechanism, which may explain electron energization at the vastly different magnetized plasma environments. The favorite configuration consists of an inhomogeneous magnetic field anchored at a given magnetic structure and excitation of whistler waves due to external injection of low-energy non-isotropic electrons. The energization proceeds as a bootstrap process due to interaction with the propagating whistler waves along the inhomogeneous magnetic field.  相似文献   

5.
The results of the investigations of chorus type VLF emissions both in the subauroral conjugate regions and along the meridional profile near the plasmapause projection are summarized in order to connect the peculiarities of ground-observed VLF chorus with the plasma processes in the magnetosphere during substorms development. The method for determination of the location of the instability region in the magnetosphere is suggested which is based on the measurement of the upper boundary frequency of the ground-observed VLF chorus (UBF-method). Dynamics of chorus spectra during the substorm development is investigated. On the basis of the revealed regularities the phenomenological model of the VLF chorus source development is constructed. The calculations of some magnetospheric plasma parameters such as plasma density, large-scale electric field etc. are carried out. The conformity between the calculated and typical measured parameters is shown. The diagnostic possibilities of VLF chorus are discussed.  相似文献   

6.
A study of simultaneous groundbased observations of I.P.D.P. (intervals of pulsation of diminishing period) magnetic field fluctuation events and satellite observations of energetic protons have been performed. Some of our results are as follows. (1) The region of I.P.D.P. occurrence is always located equatorward of the isotropic proton precipitation. (2) The I.P.D.P. generation is not connected with the poleward leap of the aurora and the poleward expansion of the precipitating protons. (3) In the evening to afternoon sector enhanced pitch angle scattering is found near L = 4 during I.P.D.P. events, earlier shown to be associated with ion cyclotron resonance. (4) I.P.D.P. events seem to be associated with increased fluxes of (40–60) keV protons injected during substorms near the plasmapause in the equatorial plane.In order to explain the observations we invoke the following model: at substorm onset ring current protons are injected deep into the nightside magnetosphere covering a certain region in L and L.T., with the inner edge of the proton population following McIlwain's injection boundary. The protons drift azimuthally westward and generate ion cyclotron waves in a certain L interval at or inside the plasmapause. By taking into account the shape and position of the plasmapause and the injection boundary, the exterrt and position of the wave generating region can be determined. The frequency-time dispersion of the I.P.D.P. is largely attributed to the L-dependent drift velocity of protons in a narrow energy band. The model is able to explain the observations during several individual events. Also, the model predicts the general trends that have been found by statistical analysis of I.P.D.P. events and accounts for the constant frequency observed by satellites during I.P.D.P. events.  相似文献   

7.
Based on all of the OGO-5 light ion density measurements (covering the period from March, 1968 to May, 1969), a definition of “isolated plasma regions” was employed to locate the most prominent patches of enhanced light ion densities in the midst of the depleted region, outside of the main plasmasphere. On the dayside, the distribution of these isolated plasma in L.T. vs. L coordinates was quite similar to that of the “detached plasma regions” by Chappell (1974a). On the nightside, however, the new distribution revealed more frequent occurrence of these regions. Elongated thick plasmatails produced during periods of sudden enhancement of convection electric fields and subsequentially thinning and corotating of the plasmatails during quieting periods, in general, could account for the statistical distribution as well as the individual events, such as those between March 27 and April 2, 1968 and Oct. 21 and Oct. 24, 1968. As demonstrated by Kivelson (1976), wave-particle interactions could produce tremendously complicated structures observed in the near vicinity of the plasmapause and far away from the plasmasphere. Examination of H+ and He+ density measurements for period of Aug. 12–Aug. 20, 1968 indicated that the density reduction of the plasmasphere during a magnetic storm was on the same order of magnitude as that obtained from whistler techniques during a magnetospheric substorm.  相似文献   

8.
Simultaneous auroral and whistler data from SANAE, Antarctica, show that the separation between the equatorward boundary of the diffuse aurora and the plasmapause lies between zero and 0.25 L. There is also some evidence to suggest that auroral precipitation occurs, at least partly, on closed field lines.  相似文献   

9.
We consider the movement of individual electrons in a magnetized plasma in which a monochromatic wave is propagating in the whistler mode. We derive simple expressions which give the displacement of the electrons as a function of time, the phase angle that their velocity vector makes with the magnetic component of the wave, their pitch angle and energy changes. A useful formula is obtained which gives the velocity range over which particles remain trapped inside the wave, as a function of the wave intensity and of the initial phase angle of the particle. It is shown that even strictly resonant particles can escape from the wave when their initial phase angle is very small. From the derived expressions, it is possible to compute the phase-bunching effect which occurs approximately at one trapping wavelength behind the leading edge of the interaction region. We deduce also the total amount of energy which is taken from (or given to) the wave by magnetospheric electrons in both cases of naturally existing or artificially injected particles. It is shown that these non-linear amplification processes can lead to very large VLF amplitude in the magnetosphere.  相似文献   

10.
This paper discusses the experimental results on electron precipitation in a diffuse aurora obtained by a sounding rocket launched from ANDENES (L ～ 6·2) on 3 November 1968. A considerable increase in the intensity of low energy electrons, Ee ? 5 keV, followed a large precipitation of more energetic electrons Ee ? 5 keV. From the observation of angular distributions and an estimate of the diffusion coefficient (Dα ? 10?3 (sec)?2), it is suggested that this higher energy precipitation is induced by gyroresonant interactions of magnetospheric electrons with radiation in the whistler mode. The lower energy precipitation separated in time and/or space, shows quasi-periodic modulations in the 5–15 sec range with periods close to the bounce period. It is suggested that this precipitation is the result of bounce-resonance interactions with electrostatic waves in the equatorial plane. Finally, from a comparison between the experimental energy spectra and plasma sheet spectra it can be concluded that these electrons are injected from the plasma sheet during a substorm and are then diffused and precipitated by energy dependent mechanisms.  相似文献   

11.
An impulsive event observed from the nightside geostationary orbit by the GEOS-2 European satellite is analysed in detail in the case of a very quiet magnetosphere. It is characterized by a very sharp and steep plasma density gradient observed near 2230 L.T. A quite detailed picture of the situation can be sketched as a result of the GEOS-2 set of experiments. The observations roughly organize themselves as follows along the geostationary orbit: an intense and well localized d.c. electric field appeared between the outbound crossing of the plasmapause and local midnight; at the same time a sudden ULF activity arose probably indicating the presence of field-aligned currents; GEOS-2 then entered a quieter plasmasheet where clear diamagnetic effects are evidenced. These observations are consistent with a stabilization of a possible interchange instability, which would maintain the density gradient at the plasmapause. The validity of the plasma density measurements which are made through an active wave method is discussed in connection with the 2 keV mean energy of the plasmasheet particles. The macroscopic evolution equation of the plasma bulk velocity is considered. It appears that the gradients of the macroscopic drift velocity of the plasma may have a non-negligible effect rendering invalid the unsophisticated scheme of a balance between kinetic and magnetic pressures.  相似文献   

12.
During August 1972, Explorer 45 orbiting near the equatorial plane with an apogee of ～5.2 Re traversed magnetic field lines in close proximity to those simultaneously traversed by the topside ionospheric satellite ISIS 2 near dusk in the L range 2.0–5.4. The locations of the Explorer 45 plasmapause crossings (determined by the saturation of the d.c. electric field double probe) during this month were compared to the latitudinal decreases of the H+ density observed on ISIS 2 (by the magnetic ion mass spectrometer) near the same magnetic field lines. The equatorially determined plasmapause field lines typically passed through or poleward of the minimum of the ionospheric light ion trough, with coincident satellite passes occurring for which the L separation between the plasmapause and trough field lines was between 1 and 2. Hence, the abruptly decreasing H+ density on the low latitude side of the ionospheric trough is not a near earth signature of the equatorial plasmapause. Vertical flows of the H+ ions in the light ion trough as detected by the magnetic ion mass spectrometer on ISIS were directed upward with velocities between 1 and 2 km s?1 near dusk on these passes. These velocities decreased to lower values on the low latitude side of the H+ trough but did not show any noticeable change across the field lines corresponding to the magnetospheric plasmapause. The existence of upward accelerated H+ flows to possibly supersonic speeds during the refilling of magnetic flux tubes in the outer plasmasphere could produce an equatorial plasmapause whose field lines map into the ionosphere at latitudes which are poleward of the H+ density decrease.  相似文献   

13.
On 26 July 1967, a magnetically quiet day (ΣKp = 12?) with high whistler activity at Halley Bay, it was found possible, by measurement of whistler nose-frequency and dispersion and the bearings of the whistler exit points, to make a detailed study of the magnetospheric structure associated with the whistler ducts.During the period 0509–2305 UT most of the exit points of whistlers inside the plasmasphere were situated along a strip about 100km wide passing through Halley Bay in an azimuthal direction 30°E of N between 57° and 62° invariant latitude. A mechanism which can give rise to such a well-defined locus which co-rotates with the Earth is not clear. Nevertheless, it does appear that the locus coincides with the contour of solar zenith angle 102° at 1800 UT 25 July. This was also the time of occurrence of a sub-storm and it is suggested that the magnetospheric structure was initiated by proton precipitation along the solar zenith angle 102° contour.At mid-day knee-whistlers observed outside the plasmapause had exit points which were closely aligned along an L-shell at an invariant latitude of 62.5°. They exhibited a marked variation (~ 3:1) in electron tube content over about 12° of invariant longitude and a drift of about 8 msec?1 to lower L-shells.Throughout the period of observation the plasmapause lay about 2° polewards of the mean position found by Carpenter (1968) for moderately disturbed days.  相似文献   

14.
Explorer 45 traversed the plasmapause (determined approximately via the saturation of the d.c. electric field experiment) at near-equatorial latitudes on field lines which were crossed by Ariel 4 (~600km altitude) near dusk in May 1972 and on field lines which were crossed by Isis II (~1400km altitude) near midnight in December 1971 and January 1972. Many examples were found in which the field line through the near-equatorial plasmapause was traversed by Explorer 45 within one hour local time and one hour universal time of Ariel and Isis crossings of the same L coordinate. For the coincident passes near dusk, the RF electron density probe on Ariel detected electron density depletions near the plasmapause L coordinates when Ariel was in darkness. When the Ariel passes were in sunlight, however, electron depletions were not discernable near the plasmapause field line. On the selected near-midnight passes of Isis II, electron density depressions were typically detected (via the topside sounder) near the plasmapause L coordinate. The dusk Ariel electron density profiles are observed to reflect O+ density variations. Even at the high altitude of Isis near midnight, O+ is found to be the dominant ion in the trough region whereas H+ is dominant at lower latitudes as is evident from the measured electron density scale heights. In neither local time sector was it possible to single out a distinctive topside ionosphere feature as an indicator of the plasmapause field line as identified near the equator. At both local times the equator-determined plasmapause L coordinate showed a tendency to lay equatorward of the trough minimum.  相似文献   

15.
The latitudinal morphology of > 100 keV protons at different local times has been studied as a function of substorm activity. A characteristic pattern is found: during quiet-times there is an isotropic zone centred around 67° near midnight, but located on higher latitudes towards dusk and dawn. This zone moves slightly equatorward during the substorm growth phase. During the expansive phase the precipitation spreads poleward apparently to ~ 71° near midnight. The protons are precipitated over a large local time interval on the nightside, but the most intense fluxes are found in the pre-midnight sector. A further poleward expansion, to more than 75° near midnight, seems to take place late in the substorm. Away from midnight, the expansion reaches even higher latitudes. During the recovery phase the intensity of the expanded region decreases gradually; the poleward boundary is almost stationary if the interplanetary magnetic field (IMF) has a northward component and no further substorm activity takes place. Mainly protons with energy below ~ 500 keV are precipitated in the expanded region. On the dayside no increase in the precipitation rates is found during substorm expansion, but late in the substorm an enhanced precipitation is found, covering several degrees in latitude. The low-latitude anisotropic precipitation zone is remarkably stable during substorms. A schematic model is presented and discussed in relation to earlier results.  相似文献   

16.
It is suggested that changes in the electric field in the night-side auroral zone and polar cap observed during the expansion phase of a substorm are related to a change in the magnetospheric flow pattern. During the substorm growth phase the flow appears to be fairly uniform across the width of the magnetosphere (uniform electric field across the tail), while at expansion the observations are consistent with the magnetospheric potential drop in the tail falling across a narrow region near the dusk magnetopause. Such non-uniform electric fields in the tail have been predicted by recent theoretical work. A rather speculative interpretation of events during a magnetospheric substorm is presented.  相似文献   

17.
The Galileo spacecraft encountered the inner magnetosphere of Jupiter on its way to a flyby of Amalthea on November 5, 2002. During this encounter, the spacecraft observed distinct spin modulation of plasma wave emissions. The modulations occurred in the frequency range from a few hundred hertz to a few hundred kilohertz and probably include at least two distinct wave modes. Assuming transverse EM radiation, we have used the swept-frequency receivers of the electric dipole antenna to determine the direction to the source of these emissions. Additionally, with knowledge of the magnetic field some constraints are placed on the wave mode of the emission based on a comparative analysis of the wave power versus spin phase of the different emissions. The emission appears in several bands separated by attenuation lanes. The analysis indicates that the lanes are probably due to blockage of the freely propagating emission by high density regions of the Io torus near the magnetic equator. Radio emission at lower frequencies (<40 kHz) appears to emanate from sources at high latitude and is not attenuated. Emission at is consistent with O-mode and Z-mode. Lower frequency emissions could be a mixture of O-mode, Z-mode and whistler mode. Emission for shows bands that are similar to upper hybrid resonance bands observed near the terrestrial plasmapause, and also elsewhere in Jovian magnetosphere. Based on the observations and knowledge of similar terrestrial emissions, we hypothesize that radio emission results from mode conversion near the strong density gradient of the inner radius of the cold plasma torus, similar to the generation of nKOM and continuum emission observed in the outer Jovian magnetosphere and in the terrestrial magnetosphere from source regions near the plasmapause.  相似文献   

18.
A quasilinear model for hiss-type mid-latitude VLF emissions is presented. It can be considered as an improved version of the models which were earlier suggested by Etcheto et al. (1973) and Sazhin (1977). When using this model it is predicted that the considered emissions are excited near the inner boundary of the plasmapause by the electrons in the energy range 2–5 keV, which is compatible with the available experimental data.  相似文献   

19.
Thermal H+ distributions have been measured as the European Space Agency GEOS-1 satellite passed through the late morning equatorial magnetosphere, plasmapause and plasmasphere. The unique capabilities of the on-board Supralhermal Plasma Analysers (SPA) have been used to overcome the retarding floating potential of the satellite and measure the velocity distribution of the cold protons. In the magnetosphere an enhanced source cone of such ions with a temperature of ~ 0.5 eV is a signature of the filling process occurring outside the plasmapause where flux tubes are relatively empty. In the plasmasphere the thermal H+ is essentially isotropic with a temperature less than 0.5 eV but the motion of the satellite introduces apparent drift.These measurements of cold proton velocity distribution now permit a reappraisal of the definition of the “plasmapause”. It becomes inappropriate to use an arbitrary empirical density, e.g. the conventional 10 cm ?3, in order to establish a boundary. It is now possible to identify a plasmapause interaction region where the two cold proton populations co-exist. This region generally lies Earthward of the 10 cm ?3 density level, has a width which is strongly dependent on magnetic activity and the temperature is typically between 0.5 and 1.5 eV. The change from “filled” to “unfilled” flux tubes relates to the physical processes which are occurring and the controlling electric field configuration; in particular, the last closed equipotential. Throughout this region, in going from the plasmasphere to the magnetosphere, the plasma drift motion is expected to change from corotation to a convection which is controlled by E ×B, and is predominantly Sunward due to the dawn-dusk electric field. Crossing the plasmapause on the morning side, little change in drift direction should occur but subtle variations in the ionic velocity distribution do reflect the change in the degree of flux tube density equilibrium.Our first direct measurement of the magnetospheric E × B drift has been reported previously but here measurements from a selected six day period show how the plasma in the plasmapause region responds to changing magnetospheric activity. The drift velocities cannot he derived with high accuracy but the analysis shows that the technique can provide a valid mapping of the magnelospheric electric field. In addition, since the magnetospheric cold plasma distribution is observed after it has come from the ionosphere, a distance of many Earth radii, the scattering and accelerating mechanisms along the flux tube can be studied. For this particular data-set taken in the late morning, the maximum potential drops along the flux tubes were less than a volt. The ionospheric proton source cone is observed to be broad, pitch angle scattering persists up to 40 or even 70°.Although these results throw new light on the plasmaspheric filling process one must recognise that, however the plasmapause is defined, it is not a simple matter to map this boundary from the equatorial plane down to low altitudes and the mid-latitude trough.  相似文献   

20.
Relativistic whistler wave mode with a perpendicular AC electric field has been studied for generalized distribution function with an index j, which is reducible to bi-Maxwellian for j = 0, loss-cone for j = 1 and delta function for j = ∞. Based on particle trajectories, the dispersionrelation is obtained using the techniques of a kinetic approach anda method of characteristic solutions Calculations are compassed with observations of low frequency waves of Voyager 2 The growth rates for the plasma parameters suited to the magnetosphere of Uranus are obtained. It is inferred that, not the magnitude but the frequency of the AC field, influences the growth rate. In addition to the temperature anisotropy, plasma particles having a loss-cone provide an additional source of energy. The relativistic electrons along with increasing the growth rate, widen the band width so as to cover a wide frequency range thus may explain the entire spectrum of whistler emissions at Uranian bow shock. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

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