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1.
Simultaneous optical and particle data from the ISIS-2 satellite are used to characterize polar cap arcs. Polar cap arcs are identified from two-dimensional geomagnetic transforms of the optical data along with precipitating electron data for the time at which the satellite is on the field line intersecting the arc. No precipitating protons were detected for any of the arc crossings. The pitch angle. distribution of the precipitating electrons is generally isotropic and the differential electron spectra show enhancements in the flux in the 300–750 eV energy range. The average energy of the precipitating electrons for the different arcs ranges from about 300 to 600 eV. A possible explanation of the observed precipitating particle characteristics is that parallel electric fields are accelerating polar rain type spectra at an altitude of several thousand km. For the arc crossings reported here the equivalent 4278 Å emission rate per unit energy deposition rate has a mean value of 162 R/(erg cm?2 s?1). Average 3914 Å intensities are about 0.8 kR while 6300 Å intensities range from 0.5 to 3 kR. Model calculations indicate that direct impact excitation is a minor source for the 5577 Å emission rate, but supplies approx. 40% of the 6300 Å emission.  相似文献   

2.
Low altitude satellite measurements of protons in the 1–100 keV range indicate two energy dependent proton precipitation boundaries. At low invariant latitudes mostly below 60° there is a region of moderately weak proton precipitation. The poleward boundary of this region tends to be at higher latitudes for the high energy protons than for the low energy protons. At high invariant latitudes there is a region where both the low and high energy protons precipitate with an isotropic pitch-angle distribution. The equatorward boundary of this region tends to be at lower latitudes for protons with energy more than 100 keV than for those in the 1–6 keV range. This region with isotropic pitch-angle distribution is located well outside the plasmapause both for the 1–6 and 100-keV protons.Between these two precipitation zones there is a region where the proton pitch-angle distribution is highly anisotropic with almost no protons in the loss cone. This region tends to be wider and more pronounced in the 1–6 than in the 100-keV protons.These findings lend further support to the mechanism of ion-cyclotron instability as the cause of proton pitch-angle diffusion in the low and intermediate regions. The process responsible for the strong diffusion at auroral latitudes has not yet been identified.  相似文献   

3.
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   

4.
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   

5.
Simultaneous observations of precipitating electrons and protons in the energy range from 15 eV to 35 keV and magnetic field variations were made onboard a sounding rocket payload launched from the Andoya Rocket Range. The electric current density deduced from the electron precipitation observed during the passage over an auroral arc was comparable to that determined from the magnetic field variations. In addition, a downward current was observed by its magnetic field signature at the northern edge of the arc which was, however, not accompanied by significant particle fluxes in the energy range under consideration. It will be assumed that this current was carried by thermal electrons of ionospheric origin.  相似文献   

6.
Electron spectra obtained during the flight of Black Brant VB-31 on August 17, 1970 through a stable aurora to a height of 268 km have been analyzed in detail to obtain the pitch angle distributions from 25 to 155° and the electron energy distributions over an energy range of 18 keV to 20 eV through the region of atmospheric interaction down to 97 km. Backscatter ratios for 140° pitch angle range from 0.065 for 18 keV electrons to 0.22 for 1 keV electrons. Backscatter of lower energy electrons decreases with atmospheric depth below 200 km. The effect of the interactions between auroral electrons and the atmosphere is such as to give a peak in electron flux which moves progressively to higher energies with penetration depth. The secondary electron flux increases monotonically with height up to 200 km. The secondary electron spectrum can be approximated by an energy power over small energy ranges but its form is somewhat dependent on height and on the primary electron spectrum.  相似文献   

7.
Energy spectra and pitch angle distributions of auroral electrons in the energy range 2.5–11 keV observed on a rocket flight launched from Andøya on 13 November 1970 are presented. Strong rapidly fluctuating fluxes during the first part of the flight were succeeded by fluxes below or close to the level of detectability. Before the rocket passed through the northern precipitation boundary two spectral events of “inverted V” character occurred. Both events were associated with field aligned pitch angle distributions. While anisotropies with the flux peaked near 0° were in general associated with the spectral peak energy, isotropy over the upper hemisphere was the dominant distribution for other energies. The observations made during these events provide strong support for the theory of a parallel potential drop close to the ionosphere as an important accelerating mechanism for auroral electrons in connection with “inverted V” events.  相似文献   

8.
The first simultaneous (within 6 min) observations of the low altitude polar cusp regions in the conjugate hemispheres are reported here based on two events detected by the DMSP-F2 and F4 satellites within the same geomagnetic local time sector. It is found that the electron spectra in the cusp are identical in the opposing hemispheres. In one case the observed latitudinal location and extent of the cusps are the same at the two hemispheres. However, in the other case the location of the equatorward boundary of the cusp regions differs by about 2° with drastically different spatial features. It is also found that in one of the events the plasma sheet electron precipitation regions overlap with the cusp regions at lower latitude in both hemispheres. The poleward boundary of these overlapping regions is located at the same latitude on either hemisphere, suggesting that this is the latitude of the last closed field line and that the cusp electrons are present on both closed and open magnetic field lines.  相似文献   

9.
It is shown that electrostatic fields parallel (E11) to the geomagnetic field cannot be the major mechanism that accelerates charged particles to auroral energies. Principal arguments are that electron and proton precipitation occur simultaneously, and also that precipitated electrons with energies less than 100 eV are found to accompany the electrons with energies of 1–10 keV that excite auroral luminosity. It is further shown that essentially all the ambient plasma in an entire tube of flux is required to sustain this intense low-energy precipitation, and this places a severe constraint on any replenishment process. It is found that generally the upper limit to (E11) throughout the auroral regions of the ionosphere and magnetosphere is of order 10 μV/m and it may be appreciably less. Relevant measurements are reviewed briefly. It is concluded that while there may occasionally be significant E11 fields, they play only a minor role-if any-in auroral phenomena.  相似文献   

10.
A statistical study of the cusp plasma has been performed using mainly electron data from the LPS, Rome, plasma experiment flown onboard HEOS-2. We have located the cusp by means of 35–50 eV electrons, from 1.5 to 2.5RE (south pole) and from 3RE up to 11RE (north pole) at 60–70° SM latitude within ±60° of SM longitude from the noon meridan plane. The average cusp thickness is 4.2° of invariant latitude. The location of the cusp in invariant latitude around the noon meridian plane depends on the IMF component BzGSM according to the linear best fit: Λ = 78.7° + 0.48BzGSM(γ). Away from the noon meridian plane the invariant latitude of the cusp decreases from 79–84° to 70–74° (at ±50° SM Longitude). At the equatorward edge of the north pole cusp, at all radial distances and at all SM longitudes, we have found a population of electrons with a harder energy spectrum than in the cusp itself. These electrons show a peak at 170–280 eV in our data. They are not the cusp (35–50 eV) electrons and are easily distinguishable from the 1 keV magnetospheric electrons. In the south pole auroral oval they are found at any SM longitude mainly poleward of the 1 keV electrons. The cusp electrons (35–50 eV) and protons have anisotropies that vary with radial distance and SM latitude, both flowing earthward more or less along the magnetic field.  相似文献   

11.
Energy spectra and angular distributions of auroral electrons in the energy range 0.2–16 keV measured by the low-altitude polar orbiting satellite ESRO 4 are presented. The observations were made in the altitude range 800–1000 km near magnetic midnight. Energy-time spectrograms show inverted-V structures with peaked energy spectra. The inverted-V events are associated with anisotropic electron pitch angle distributions peaked at 0 deg. Frequently these distributions have a maximum also at 90 deg. Measurements of >43 keV electrons indicate that the acceleration probably occurs on closed field lines. It is found that many properties of the observed particle distributions can be explained by acceleration in an electric field parallel to the magnetic field lines, if trapping of particles under an increasing potential drop is included in the model.  相似文献   

12.
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   

13.
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   

14.
The irreversible changes of the intensity of trapped protons with energy above 1 MeV in the Earth's magnetosphere near the outer boundary of trapping are observed after moderate geomagnetic storms on the low-altitude polar-orbiting satellite Intercosmos-17. These changes are interpreted in terms of nonadiabatical effects of proton motion in the disturbed geomagnetic field (assuming Dst variation) which affects the conditions for stable trapping of protons during the storm. The decrease of proton intensity is due to an adiabatic decrease of energy, an increase of mirror-point altitude and nonadiabatic scattering and losses. The interaction of two types of particle motion—gyrorotation and the ‘bounce’ motion, which leads to the instability of motion, is assumed. The importance of nonadiabatical losses of trapped protons with low equatorial pitch angles for changes near the proton boundary is pointed out.  相似文献   

15.
The topology of the boundaries of penetration (or inversely the boundaries of the forbidden regions) of 90° pitch angle equatorial protons with energies less than 100 keV are explored for an equatorial convection E-field which is directed in general from dawn to dusk. Due to the dependence of drift path on energy (or magnetic moment) complex structural features are expected in the proton energy spectra detected on satellites since the penetration distance of a proton is not a monotonically increasing or decreasing function of energy. During a storm when the convection E is enhanced, model calculations predict elongations of the forbidden regions analogous to plasmatail extensions of the plasmasphere. Following a reduction in the convection field, spiral-structured forbidden regions can occur. Structural features inherent to large scale convection field changes may be seen in the noselike proton spectrograms observed near dusk by instrumentation on the satellite Explorer 45 (S3) (Smith and Hoffman, 1974). These nose events are modelled by using an electric field model developed originally by Volland (1973). The strength of the field is related to Kp through night-time equatorial plasmapause measurements.  相似文献   

16.
keV protons observed by the ESRO 1A satellite in the upper atmosphere equatorward of the main precipitation zone are described and discussed. The protons are highly anisotropic (empty loss cone) between the low-latitude boundary of the main precipitation zone and approximately L=4 during quiet and moderately disturbed conditions (Kp=0?4). Between L=4 and L=2.7 the proton flux is generally enhanced compared to that at L values somewhat above 4 and only moderately anisotropic. Substorms push the outer main precipitation zone equatorwards, but the boundaries of the innermost, moderately anisotropic region (at L=2.7 and L=4) move only when strong magnetic storms compress the plasmasphere to within L=4. It is suggested that the moderately anisotropic zone is caused by the ion-cyclotron instability for which the growth rate may have a broad maximum between about L=2.7 and L=4. For proton energies in the keV range the instability is excited only in regions with cold plasma densities above several hundred ions per cubic centimeter. It is finally concluded that the observations of low-latitude proton precipitation lend further support to the mechanism of ion-cyclotron instability as the cause of proton pitch angle diffusion, as proposed by Cornwall et al. (1970).  相似文献   

17.
The pitch-angle distributions in and near the loss cone, of ～ (100–200) and ～ (200–350) keV protons observed by the ESRO IB satellite during the period 7–15 October 1969 are presented. The data include periods of relative quiet as well as more disturbed geomagnetic conditions. Spatial characteristics and dynamics of the protons, both on the night-and dayside of the Earth are described. The actual pitch-angle distribution is interpreted as produced by wave-particle interactions, and the diffusion coefficient and lifetime against pitch angle scattering have been estimated from existing theories. During slightly disturbed conditions, the observations suggest an average random walk in pitch angle made by a particle during a crossing of the diffusion region of about one half of the loss cone half angle for 4 ? L ? 6. The lifetime against pitch angle scattering into the loss cone is found to be somewhat less than the charge exchange lifetime for these (100–350) keV protons. The spectral density of interacting waves is tentatively estimated to about 0·1 γ2Hz, and compares with estimates arrived at from completely different approaches.  相似文献   

18.
Photoelectron flux in the energy range 6–70 eV coming from the sunlight conjugate ionosphere has been measured directly by the rocket borne low energy electron spectrometer in the altitude region of 210–350 km. Pitch angle distribution of the measured flux is nearly isotropic, the flux decreasing slightly with pitch angle. The photoelectron fluxes measured at 350 km at the energies of 15 and 30 eV are 3 × 106 and 1 × 106 (cm2 s str eV)?1 respectively which decrease to 1 × 106 and 1 × 105 at 250 km at the same energies. These values are consistent with the vertical profile of the 630 nm airglow intensity measured simultaneously. The fluxes obtained near apogee show peaks in the range 20–30 eV which also appear in the daytime photoelectron flux, indicating reduced loss of electrons during the passage from the conjugate ionosphere through the plasmasphere at the low geomagnetic latitude where observation was made. Photoelectron fluxes observed below the apogee height are compared to the calculated fluxes to investigate the interaction of electrons with the atmospheric species during the passage in the ionosphere. Calculated fluxes obtained by using continuous slowing-down approximation and neglecting pitch angle scattering are in good agreement with the observations although there still remain disagreements in detailed comparison which may be ascribed to the assumptions inherent in the calculation and/or to the uncertainties of the input data for the calculation.  相似文献   

19.
We present Cassini data revealing that protons between a few keV and about 100 keV energy are not stably trapped in Saturn's inner magnetosphere. Instead these ions are present only for relatively short times following injections. Injected protons are lost principally because the neutral gas cloud converts these particles to energetic neutral atoms via charge exchange. At higher energies, in the MeV to GeV range, protons are stably trapped between the orbits of the principal moons because the proton cross-section for charge exchange is very small at such energies. These protons likely result from cosmic ray albedo neutron decay (CRAND) and are lost principally to interactions with satellite surfaces and ring particles during magnetospheric radial diffusion. A main result of this work is to show that the dominant energetic proton loss and source processes are a function of proton energy. Surface sputtering by keV ions is revisited based on the reduced ion intensities observed. Relatively speaking, MeV ion and electron weathering is most important closer to Saturn, e.g. at Janus and Mimas, whereas keV ion weathering is most important farther out, at Dione and Rhea.  相似文献   

20.
Energy spectra of electrons between 30 eV and 18 keV were obtained with a spectrometer on a Black Brant rocket launched from Cape Parry, N.W.T. (Λ = 75.2°) on December 6, 1974 to study the dayside magnetospheric cleft. The rocket flew to an apogee of 236 km and travelled poleward to 80° invariant latitude. The cleft was observed to extend from 76.9 to 78.4° invariant latitude. Equatorward of this electrons of a few keV energy were observed with a total energy flux of up to 2 erg/cm2 sec ster. Variable fluxes of electrons with a spectrum fitted by a Maxwellian distribution of 150 eV characteristic energy were observed through most of the cleft. One inverted V structure was crossed. In that region, the electron energy increased to 650 eV and a total energy flux of 8 erg/cm2 sec ster was measured. The event was a temporal one and only a few km in width, as deduced from optical data. Fluxes of about 10−2 erg/cm2 sec ster were recorded poleward of the cleft.  相似文献   

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