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1.
Latitudinal characteristics of ELF hiss in mid- and low-latitudes have been statistically studied by using ELF/VLF electric field spectra (50 Hz-30 kHz) from ISIS-1 and -2 received at Kashima station, Japan from 1973 to 1977. Most ISIS ELF/VLF data observed in mid- and low-latitude include ELF hiss at frequencies below a few kHz. The ELF hiss has the strongest intensity among VLF phenomena observed by the ISIS electric dipole antenna in mid- and low-latitudes, but the ELF hiss has no rising structure like the chorus in the detailed frequency-time spectrum. The ELF hiss is classified into the steady ELF hiss whose upper frequency limit is approximately constant with latitude and the ELF hiss whose upper frequency limit increases with latitude. These two types of ELF hiss occur often in medium or quiet geomagnetic activities. Sometimes there occurs a partial or complete lack of ELF hiss along an ISIS pass.Spectral shape and bandwidth of ELF hiss in the topside ionosphere are very similar to those of plasmaspheric hiss and of inner zone hiss. The occurrence rate of steady ELF hiss is about 0.3 near the geomagnetic equator and decreases rapidly with latitude around L = 3. Hence it seems likely that ELF hiss is generated by cyclotron resonant instability with electrons of several tens of keV in the equatorial outer plasmasphere beyond L = 3.Thirty-seven per cent of ELF hiss events received at Kashima station occurred during storm times and 63% of them occurred in non-storm or quiet periods. Sixty-seven per cent of 82 ELF hiss events during storm times were observed in the recovery phase of geomagnetic storms. This agrees with the previous satellite observations of ELF hiss by search coil magnetometers. The electric field of ELF hiss becomes very weak every 10 s, which is the satellite spin period, in mid- and low-latitudes, but not near the geomagnetic equator. Ray tracing results suggest that waves of ELF hiss generated in the equatorial outer plasmasphere propagate down in the electrostatic whistler mode towards the equatorial ionosphere, bouncing between the LHR reflection points in both the plasmaspheric hemispheres.  相似文献   

2.
Intensities of auroral hiss generated by the Cerenkov radiation process by electrons in the lower magnetosphere are calculated with respect to a realistic model of the Earth's magnetosphere. In this calculation, the magnetic field is expressed by the “Mead-Fairfield Model” (1975), and a static model of the iono-magnetospheric plasma distribution is constructed with data accumulated by recent satellites (Alouette-I, -II, ISIS-I, OGO-4, -6 and Explorer 22). The energy range of hiss producing electrons and the frequency range of the calculated VLF are 100–200 keV, and 2–200 kHz, respectively. Intensities with a maximum around 20 kHz, of the order of 10?14 W/m2/Hz1 at the ground seem to be ascribable to the incoherent Cerenkov emission from soft electrons with a differential energy spectrum E?2 having an intensity of the order of 108cm?2/sec/sr/eV at 100 eV. It is shown that the frequency of the maximum hiss spectral density at geomagnetic latitudes 80° on the day-side and 70° on the night-side is around 20 kHz for the soft spectrum (～E?2) electrons, which shifts toward lower frequency (～10 kHz) for a hard spectrum (～E?1·2) electrons. The maximum hiss intensity produced by soft electrons is more than one order higher than that of hard electron produced hiss. The higher rate of hiss occurrence in the daytime side, particularly in the soft electron precipitation zone in the morning sector, and the lesser occurrence of auroral hiss in night-time sectors must be, therefore, due to the local time dependence of the energy spectra of precipiating electrons rather than the difference in the geomagnetic field and in the geoplasma distributions.  相似文献   

3.
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   

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.
Vertical profiles of electron density obtained in the vicinity of the plasmapause using the Alouette-II topside sounder have been analyzed to assess the presence of H+ flow in the topside ionosphere. The observations in the midnight sector show clearly the presence of the plasmapause; i.e. there is a sharp boundary separating the poleward regions of polar wind H+ flow and the more gentle conditions of the plasmasphere where light ions are present in abundance. In contrast, in the sunlit morning sector upwards H+ flow is deduced to be present to invariant latitudes as low as 48° (L = 2·2) in the regions normally known to be well inside the plasmasphere. The upwards H+ flux is sufficiently large (3 × 108 ions cm?2 sec?1) that the plasmapause cannot be seen in the latitudinal electron density contours of the topside ionosphere. The cause for this flow remains unknown but it may be a result of a diurnal refilling process.  相似文献   

6.
Unusual auroral emission at mid-latitudes, showing nearly exclusively the green oxygen line (557.7 nm) and occurring during the early part of the recovery phase after strong magnetic storms is described. The emission has a life-time of up to several hours, consists of cloud-like patches and appears quite isolated at medium latitudes with no simultaneous aurorae at higher latitudes. The name “post-storm mid-latitude green aurora” is proposed for this emission. For the event observed during the night of 29–30 August 1978, additional ionospheric measurements from heights below the mid-latitude aurora (?min, A3-LF data) are available from nearby observations. Our investigation shows that the emission was observed just at the beginning of a post-storm effect (PSE) in ionospheric absorption. The optical and absorption data have been used to extract information on precipitating high-energy electrons, assumed to be the cause of both the optical emisson and the excessive absorption. During the night in question precipitating electrons with fluxes above the quiet-time level and energies upto at least 200 keV were found in a region extended in latitude (2.7 < L < 3.3) and probably even more extended in longitude. Latitudinally narrow bands, elongated along shells of constant L, with extremely high fluxes of 10–20keV electrons (according to our estimates at least 5. 107 el cm?2s?1) were embedded within this region.  相似文献   

7.
Plasmaspheric hiss waves have been frequently invoked to explain the slow loss of the radiation belt electrons. However, the effect of hiss waves outside the plasmasphere on the radiation belt electrons remains unclear. Here, on the basis of Van Allen Probes observations and quasilinear simulations, we show that the hiss waves outside the plasmasphere are able to cause the significant precipitation loss of energetic electrons on a timescale of 1 day. In the event of interest, the hiss wave power spectra density reached up to \(10^{-6}~\mbox{nT}^{2}/\mbox{Hz}\), and the obtained pitch-angle diffusion coefficients are found to be \(10^{2}\)–\(10^{4}\) times larger than the momentum and cross diffusion coefficients. During a period of 1 day, the modeled hiss waves caused the depletion of 300–500 keV electrons by up to 10 times. These results suggest that the hiss waves outside the plasmasphere should be taken into account in the future radiation belt modeling.  相似文献   

8.
A simple model of the motion of charged particles in the closed field line magnetic field for L ? 4·5 is used together with Injun 3 measurements of 40 keV precipitated electrons made in the northern hemisphere to estimate theoretically the extent of electron precipitation, the energy input and the 3914 Å airglow in the South Atlantic geomagnetic anomaly. Using average values of the northern hemisphere precipitated electron flux, two regions of significantly enhanced electron precipitation are found in the southern hemisphere. One occurs in the region 10–20°E and 40–50°S, with L ≈ 2, and the second near 30°E and 65°S, with L ≈ 4.5. Approximately 0.04 erg cm?2 sec?1 are deposited by 40 keV electrons for 50 per cent of the time in the first region and half that amount in the second. This increases to ～0·1 and 0·02 erg cm?2 sec?1 respectively for 15 per cent of the time for near sunspot minimum conditions. The results show a gradual increase in precipitation on the western side of the anomaly followed by a rapid increase and sudden cut-off in precipitation within a few degrees west of minimum B. The flux on L = 2 reaches a “spike” in the southern hemisphere ～f35 times greater than the average flux precipitated on L = 2 in the northern hemisphere. This increase in precipitation arises from the loss of “trapped” particles to the atmosphere where the mirror heights are lowest.  相似文献   

9.
Low altitude satellite observations of precipitated and locally mirroring protons during periods of ground-based SAR arc observations are presented. The SAR arcs are found to be located in a region with significantly enhanced proton pitch angle scattering and enhanced electron temperature, but inside the plasmapause where the proton pitch angle distribution is anisotropic. The increase in the pitch angle scattering takes place in a localized region having a width of a few tenths of a L-value. The observations can favourably be accounted for by the Cornwall et al. (1971) theory for the SAR arc formation. Using observed proton fluxes and typical energy spectra, the expected Hβ intensity in the SAR arc region is estimated to be a few Rayleighs, and the energy flux from precipitated protons above a few keV to be 10?2?10?1erg/cm2s. These estimates are in reasonable agreement with previously published theoretical and experimental values. Simultaneous groundbased observations of Hα emissions were found in the region of intense, isotropic proton precipitation located outside the plasmapause.  相似文献   

10.
Energetic electron injection events result in the arrival of loss-cone distributions of electrons at energies of a few keV close to the plasmapause at local midnight. These distributions favour the growth of strong electrostatic waves with some conversion to electromagnetic nonthermal continuum emissions near to the geomagnetic equator.GEOS2 located at the geostationary orbit (L = 6.6, 3.3° South) has observed these continuum emissions for a number of electron injection events. Their unique frequency structure provides a measurement of the geomagnetic field strength at the source and hence its radial position, while direction finding measurements at GEOS2 complete the source location determination.Measurements of source locations as a function of time after the start of an electron injection event, yield typical inwards motions of 1REh?1. In this way the emissions provide a remote sensing of the plasmapause location from the geostationary orbit.  相似文献   

11.
In the midday sector, the hard electron precipitation and the associated patchy aurora at geomagnetic latitude ～65° are the only auroral features (? 20 keV) located equatorward of the dayside auroral oval during intense and moderately disturbed geomagnetic conditions. We identify the patchy luminosity in the midday and late morning sectors as the active mantle aurora. The mantle aurora was found by Sanford (1964) using the IGY-IGC auroral patrol spectrographs and which was thought to be non-visual. The precipitating electrons reside mostly at energies greater than several keV with an energy flux of ? 0.1 erg cm?2 s?1 sr?1 during geomagnetic active periods. This hard precipitation occurs in a region which is asymmetric in L.T. with respect to the noon meridian. The region extends from the morning sector to only early afternoon (13–14 M.L.T.) along the geomagnetic latitude circle of about 65–70°. The model calculation indicates that the mantle aurora is produced by the precipitation of the energetic electrons which drift azimuthally from the plasma sheet at the midnight sector to the dayside magnetopause during magnetospheric substorms.  相似文献   

12.
Extremely low frequency (ELF)/Very low frequency (VLF) hiss is whistler mode wave that interacts with energetic electrons in the magnetosphere. The characteristics features of ELF/VLF hiss observed at low latitude ground station Jammu (Geomag. lat. 22°16′ N, L=1.17) are reported. It is observed that most of hiss events first propagate in ducted mode along higher L-values (L = 4–5), after reaching lower edge of ionosphere excite the Earth-ionosphere waveguide and propagate towards equator to be received at low-latitude station Jammu. To understand the generation mechanism of ELF/VLF hiss, incoherent Cerenkov radiated power from the low-latitude and mid-latitude plasmasphere are evaluated. Considering this estimated power as an input for wave amplification through wave–particle interaction, the growth rate and amplification factor is evaluated which is too small to explain the observed wave intensity. It is suggested that some non-linear mechanism is responsible for the generation of ELF/VLF hiss.  相似文献   

13.
During the GRIF experiment onboard the Mir orbiting station, the sky was monitored with a PX-2 wide-field (～1 sr) scintillation X-ray spectrometer to detect bursts in the photon energy range 10–300 keV. Because of the comprehensive instrumentation, which, apart from the X-ray and gamma-ray instruments, also included charged-particle detectors, the imitations of astrophysical bursts by magnetospheric electron precipitations and strongly ionizing nuclei were effectively filtered out. It was also possible to separate solar and atmospheric events. Several tens of bursts interpreted as being astrophysical were detected in the experiment at sensitivity levels S～10?7 erg cm?2 (for bursts whose spectra were characterized by effective temperatures kT～100 keV) and S～3×10?8 erg cm?2 (for bursts with kT～25 keV). Some of the soft gamma-ray or hard X-ray bursts with kT～10–50 keV were identified with the bursting pulsar GRO J1744-28. Our estimate of the detection rate for cosmological soft gamma-ray or hard X-ray bursts from the entire sky suggests that the distributions of long-duration (>1 s) gamma-ray bursts (GRBs) in characteristic energy kT and duration are inconsistent with the steady-state cosmological model in which the evolution of burst sources is disregarded. Based on GRIF and BATSE/CGRO data, we conclude that most of the GRB sources originate at redshifts 1<z<5.  相似文献   

14.
Intense (? 10 mVm?1) electrostatic plasma waves near the upper hybrid frequency have been observed between ± 50° magnetic latitude during spacecraft plasmapause crossings. We present wave growth rate and three-dimensional convective amplification calculations which suggest how intense upper hybrid (IUH) events can occur over such a wide range of latitudes. The effects of wave refraction are shown to be crucial to the proper calculation of convective amplification.We first calculate upper hybrid wave growth for an IUH event at 10° MLAT during which a complete electron distribution function with a loss cone feature was measured simultaneously with the waves. We show that a parallel density gradient may be necessary to account for the observed amplification. Without such a density gradient, the dipole magnetic field gradient would quickly refract the wave vector component parallel to the local field lines out of the unstable region in wave vector space. Upon mapping the distribution function observed at 10° MLAT to other latitudes by conserving the electrons' magnetic moments, we then find that the mapped distribution could produce large amplification at higher latitudes only if there is an appropriate parallel density gradient. At the equator, the long magnetic field gradient scale length enables large amplitudes to be attained without a density gradient.The results of our UH ray tracing analysis are related to theories and observations of magnetospheric continuum radiation.  相似文献   

15.
It has been controversial whether the flare-associated hard X-ray bursts are thermal emission or non-thermal emission. Another controversial point is whether or not the associated microwave impulsive burst originates from the common electrons emitting the hard X-ray burst.It is shown in this paper that both the thermal and non-thermal bremsstrahlung should be taken into account in the quantitative explanation of the time characteristics of the hard X-ray bursts observed so far in the photon energy range of 10–150 keV. It is emphasized that the non-thermal electrons emitting the hard X-rays and those emitting the microwave impulsive burst are not common. The model is as follows, which is also consistent with the radio observations.At the explosive phase of the flare a hot coronal condensation is made, its temperature is generally 107 to 108K, the number density is about 1010 cm–3 and the total volume is of the order of 1029 cm3. A small fraction, 10–3–10–4, of the thermal electrons is accelerated to have power law distribution. Both the non-thermal and thermal electrons in the sporadic condensation contribute to the X-ray bursts above 10 keV as the bremsstrahlung. Fast decay of the harder X-rays (say, above 20 keV) for a few minutes is attributed to the decay of non-thermal electrons due to collisions with thermal electrons in the hot condensation. Slower decay of the softer X-rays including around 10 keV is attributed to the contribution of thermal component.The summary of this paper was presented at the Symposium on Solar Flares and Space Research, COSPAR, Tokyo, May, 1968.  相似文献   

16.
X-radiation may result from active plasma phenomena in the interactions of comets with the solar wind. We have carried out a limited but sensitive search for soft X-radiation from Comet Bradfield (1979l), on 1980 Feb. 5. No X-radiation was detected at a level (3σ) of 1.7 × 10?13 erg(cm2sec keV)?1 in the 0.2 – 4.0 kev range. This corresponds to a limit on the power dissipated in the comet by non-thermal electrons of approximately 1019 ergs sec?1, averaged over the 2568-sec exposure to the comet. This energy deposition is near the magnitude suggested by simple theoretical ideas, and further searches of appropriate comets both in soft X-radiation and at radio wavelengths seem warranted.  相似文献   

17.
The UCSD solar X-ray instrument on the OSO-7 satellite observes X-ray bursts in the 2–300 keV range with 10.24 s time resolution. Spectra obtained from the proportional counter and scintillation counter are analyzed for the event of November 16, 1971, at 0519 UT in terms of thermal (exponential spectrum) and non-thermal (power law) components. The energy content of the approximately 20 × 106K thermal plasma increased with the 60 s duration hard X-ray burst which entirely preceded the 5 keV soft X-ray maximum. If the hard X-rays arise by thick target bremsstrahlung, the nonthermal electrons above 10 keV have sufficient energy to heat the thermally emitting plasma. In the thin target case the collisional energy transfer from non-thermal electrons suffices if the power law electron spectrum is extrapolated below 10 keV, or if the ambient plasma density exceeds 4 × 1010 cm–3.Formerly at UCSD.  相似文献   

18.
During the GRIF experiment onboard the Mir orbiting station, cosmic gamma-ray bursts (GRBs) were observed in the photon energy range 10–300 keV. We developed a technique for selecting events, cosmic GRB candidates, based on output readings from the PX-2 scintillation spectrometer, the main astrophysical instrument. Six events interpreted as cosmic GRBs were identified at a threshold sensitivity level of ≥10?7 erg cm?2. The GRIF burst detection rate recalculated to all the sky is ～103 yr?1 (fluence ≥10?7 erg cm?2). This rate matches the BATSE/CGRO estimate and significantly differs from the value predicted by the S?3/2 dependence, which holds for a spatially uniform source distribution. The GRB detection rate at low peak fluxes is compared with the results of analysis for BATSE/CGRO “nontriggered” events and with predictions of major cosmological models. We conclude that the PX-2 observational data on faint cosmic GRBs are consistent with predictions of models with the highest frequency of GRB occurrence at z ≥1.5–2.  相似文献   

19.
Values of plasma temperature and vertical temperature gradient were obtained by fitting theoretical models to 60,000 observed electron density profiles, at heights of 400–1000 km. Results show the diurnal and seasonal changes in temperature from 75°S to 85°N near solar minimum. At night the temperature and temperature gradient are both low inside the plasmapause and high outside. Day-time temperatures increase almost linearly with latitude, from 1500 K at the magnetic equator to a maximum of 3500 K at the plasmapause. There is also a sharp peak at 77° latitude, beneath the magnetospheric cleft. Mean vertical temperature gradients are ca. 0.5 Kkm at night, and 1–4 K/km during the day. The downwards flow of heat, during the day, increases from about zero at 10° latitude to a maximum of 4 × 109eVcm2sec at the plasmapause. Night-time flows are 5–20 times less, inside the plasmasphere. Increases in magnetic activity cause a temperature increase at 400 km, of about 70 K per unit increase in Kp at all latitudes greater than 65°. The temperature peaks at the plasmapause and the magnetospheric cleft show little increase with magnetic activity, but move equatorwards by ca. 2° in latitude per unit Kp.  相似文献   

20.
Based on the observational data obtained at eleven stations along a geomagnetic meridian (Φm = 45–63°), the characteristics of pc 3, 4 pulsations are investigated. It has been shown that pc 3, 4 pulsations possess two amplitude maxima: one in the high latitudes and the other in middle latitudes. Consequently, the amplitude minimum between the two maxima is observed in subauroral latitudes (Φm ≈ 60°). Examining the peculiarities of the polarization behaviour of pc 3, 4 pulsations along the meridian array, two different regions, where the pulsations are generated, are noticed. One is situated in the middle latitudes of about 55–60°, and the other in the auroral area of about 65–70° in geomagnetic latitude. The former region corresponds to a projection of an area inside the plasmapause and the latter of an area of the outer radiation belt in the magnetosphere. The dependence of the pc 3, 4 periods on the position of the plasmapause is clarified. It is also shown that both the position of the pc 3 amplitude maximum in the middle latitudes and the position of pc 4 minimum in the subauroral area shift according to the variation in the magnetic activity and the position of plasmapause.The dynamic spectra of the simultaneous wave-packets of Pc-pulsations are investigated along the meridional profile. The maximum time delay of the Pc-signals is found at a latitude of about 57°, corresponding to the region of low values of Alfvén velocity inside the plasmasphere. On the other hand, a sharp decrease in the time delay is observed at a latitude of about 60°, the region of the rapid increase of Alfvén velocity at the plasmaspheric boundary in the magnetosphere.  相似文献   

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