共查询到20条相似文献，搜索用时 15 毫秒
1.
I. G. Richardson S. W. H. Cowley R. J. Hynds
P. W. Daly
T. R. Sanderson
K. -P. Wenzel 《Planetary and Space Science》1988,36(12):1429-1450The properties of energetic (65–95 keV) cometary water-group ions in the extended solar wind pick-up region surrounding comet Giacobini-Zinner are examined using data from the EPAS instrument on the ICE spacecraft. In the outer part of this region, extending from cometocentric distances of several hundred thousand to a few million kilometres (the limit of pick-up ion detectability), it is found that large modulations of the ion flux occur (with JMAX/JMIN 102-103) which are related to the direction of the magnetic field. It is also found that the ions stream in a direction which is intermediate between the directions of the solar wind flow and the E × B drift, and that ions are present at energies somewhat above the local pick-up energy. These properties indicate that the waves which are excited by the unstable “ring-beam” pick-up ion velocity distributions do result in significant scattering of the ions in this region, both in pitch angle and in energy, but that they have insufficient amplitude to scatter the ions into near isotropy in the solar wind frame. Closer to the comet (but still upstream from the bow shock), the ion flux modulations are considerably reduced in amplitude and the ions respond less to the E × B drift, indicating that the ions are scattered nearer to isotropy in this region. Inbound, this transition takes place relatively abruptly at a distance of 4 × 105 km in association with an increase in the solar wind speed, after which the ion flux increases, and ceases to be modulated by the field direction, while the streaming direction is continuously antisolar and unmodulated by the direction of the E × B drift. Outbound, weak vestiges of the ring-beam ion anisotropy are present in the region immediately upstream from the bow shock (at −1 × 105 km), but these become more marked at distances in excess of t4 × 105 km, increasing gradually with increasing distance from the comet. It is shown that the evolution of the ion properties is qualitatively consistent with expectations based on quasi-linear diffusion of the ions by the magnetosonic waves observed during the encounter. 相似文献
2.
B. Grandal J.A. Holtet J. Trim B. Maehlum B. Pran 《Planetary and Space Science》1980,28(12):1131-1145
The POLAR 5 sounding rocket, launched from Andøya, Norway on 1 February, 1976 was of a “mother-daughter” configuration. An electron accelerator, mounted on the “daughter,” produced a pulsed electron beam with currents up to 130 mA and electron energies up to 10 keV. The waves, artificially stimulated by the injected electron beam, was studied using wave receivers, mounted on the “mother.” The receivers covered the frequency range from 0.1 kHz to 5 MHz.
In addition to the stimulated waves observed during beam injection, enhanced wave emissions were observed 10–20 ms after the end of beam injection. This emission seemed to be relatively independent of whether the electron beam is launched up or down along the geomagnetic field.
The high frequency emission observed after beam injection is found to be correlated with the passage through an auroral arc. In particular this emission is closely correlated with the flux of 4–5 keV auroral electrons.
The low frequency emissions observed after beam injection are concentrated in two bands below the lower hybrid frequency.
Different mechanisms for explaining the observed time delays between the beam injection and the observation of the emissions are discussed. 相似文献
3.
Zhao Ren-yang Jin Sheng-zhen Fu Qi-jun Li Xiao-cong 《Chinese Astronomy and Astrophysics》1991,15(4):439-445
In this paper the observed 1.4–1.6 s quasi-periodic oscillations in the spike radiation of the microwave outburst of 1981 May 16 are analysed in teras of MHD waves. We point out that the fast magnetoacoustic waves (“sausage” mode) propagating inside and outside a loop can modulate the magnetic field and the pitch angle distribution of the electron beams in the source region. The growth rate of electron-cyclotron-maser instability is then affected to give rise to the quasi-periodic oscillations. Quantitative estimates of relevant physical parameters are given. 相似文献
4.
Simultaneous measurements of keV ions and electrons with the ESRO 1A satellite have shown the following ion characteristics among others. Ions of about 6 keV energy are strongly field-aligned on the flanks of the inverted V events (mainly through the disappearance of the ion flux near 90° pitch angle). Field-aligned electron fluxes are often found in the same regions of the inverted V events where the ions are field-aligned. At the centre of inverted V events isotropization occurs (except in some small events). The 1 keV ion flux at large pitch angles (80°) is generally not reduced very much when the 6 keV, 80° ion flux shows strongly decreased values. The ratio of the 1 to 6 keV ion flux has a maximum near the centre of an inverted V event where the electron spectrum is hardest and the 6 keV ions are isotropic (or nearly isotropic).The observations are interpreted in terms of a model with two oppositely directed field-aligned electrostatic potential drops: one upper accelerating electrons downward and one lower, produced by the electron influx, which accelerates ions downward. Ion scattering in turbulent wave fields is proposed to be responsible for the observation that the 1 keV ion flux at large pitch angles does not decrease strongly where the 6 keV ion flux does and as an explanation of the isotropization at the centre of the event. The source problem for the ions is eliminated by the precipitating electrons ionizing continuously the thin neutral atmosphere even at altitudes of a few thousand kilometers. 相似文献
5.
The COSPIN/KET experiment onboard Ulysses has been monitoring the flux of 3–20 MeV electrons in interplanetary space since the launch of Ulysses in October 1990. The origin of these electrons has been known for a long time to be the Jovian magnetosphere. Propagation models assuming interplanetary diffusion of these electrons in the ideal Parker magnetic field were successfully developed in the past. The average electron flux measured by our experiment agrees with these models for most of the times before and after the Jovian flyby of February 1992, i.e. in and out of the ecliptic down to 28° S of heliographic latitude for the last data presented here (end of March 1993).However, in addition to this average flux level well accounted for by diffusion in an ideal Parker field, we have found very short duration electron events which we call “jets”, characterized by: (i) a sharp increase and decrease of flux; (ii) a spectrum identical to the electron spectrum in the Jovian magnetosphere; and (iii) a strong first-order anisotropy. These jets only occur when the magnetic field at Ulysses lies close to the direction of Jupiter, and most of the time (86% of the events) points outwards from Jupiter, i.e. has the same polarity after the flyby as the Jovian dipole (North to South). These events are interpreted as crossings by Ulysses of magnetic flux tubes or sheets directly connected to the location of the Jovian magnetosphere from which electrons escape into interplanetary space. The average thickness of these sheets is 1011cm or 14 Jovian radii. These jets are clearly identified up to 0.4 a.u. before the Jupiter flyby in the ecliptic plane, and up to 0.9 a.u. out of the ecliptic.Moreover, the characteristic rocking of the electron spectrum in the Jovian magnetosphere with a 10 h periodicity is found to be present during the jets, and predominantly during them. In the past, this modulation has been reported to be present in interplanetary space as far as 1 a.u. upwind of Jupiter, a fact which cannot be accounted for by diffusion in the average Parker magnetic field. Our finding gives a simple explanation to this phenomenon, the 10 h modulation being carried by the “jet” electrons which travel with no appreciable diffusion along magnetic field lines with a direction far from the ideal Parker spiral. 相似文献
6.
Using a 2 1/2-D fully relativistic electromagnetic particle-in-cell code (PIC) we have investigated a potential electron acceleration mechanism in solar flares. The free energy is provided by ions which have a ring velocity distribution about the magnetic field direction. Ion rings may be produced by perpendicular shocks, which could in turn be generated by the super-Alfvénic motion of magnetic flux tubes emerging from the photosphere or by coronal mass ejections (CMEs). Such ion distributions are known to be unstable to the generation of lower hybrid waves, which have phase velocities in excess of the electron thermal speed parallel to the field and can, therefore, resonantly accelerate electrons in that direction. The simulations show the transfer of perpendicular ion energy to energetic electrons via lower hybrid wave turbulence. With plausible ion ring velocities, the process can account for the observationally inferred fluxes and energies of non-thermal electrons during the impulsive phase of flares. Our results also show electrostatic wave generation close to the plasma frequency: we suggest that this is due to a bump-in-tail instability of the electron distribution. 相似文献
7.
With an instrument on board the Japanese satellite EXOS-A electron temperatures of more than 1000 K above the “normal” values have been observed in the night-time topside F-region above the geographic region where the total magnetic field is below 20000 nT. Simultaneously enhanced wave emissions on 45 kHz, 2 MHz and 3 MHz were found and an increase in particle precipitation. The observations are described in detail and several mechanism are discussed which can explain the results. 相似文献
8.
9.
R. Gendrin 《Planetary and Space Science》1961,5(4):274-278
In this paper the question is examined of how the v.l.f. radio-waves are guided along the magnetic field. Energy passes through the magnetic field under two sets of conditions. Corresponding to the “nose-whistlers” explained by Helliwell, the first one occurs when the wave-normal itself is in the direction of the magnetic field. This does not happen in the second case when the remarkable property is also shown that all frequencies are propagated at the same velocity V0 = cƒH/2ƒ0 (ƒH gyrofrequency, ƒ0 frequency of the plasma). Considerations of energy point out that, if such a propagation is not easily observable in the case of an isotropic emission, it is not the same thing for an emission produced by
erenkov effect, which is able to produce all energy by this mode of propagation, provided the particle's velocity has a low fixed value (˜ 10,000 km/sec in the exosphere). All frequencies being emitted at the same time and following the same path wtih the same velocity, we can explain the broadband noise observed during the reception of whistlers. The required velocity of particles is exactly the velocity V0. This coincidence is explained in an appendix, and extended to other anisotropic media. 相似文献
10.
The medium energy particle spectrometer (electrons of energy > 20 keV, protons > 25 keV) on board ISEE-2 has measured very similar pitch angle distributions and intensities during “flux transfer” events in the magnetosheath and events previously designated as “inclusion” events in the magnetosphere on a single pass through the magnetopause. This is interpreted as strong evidence that magnetic field lines in the magnetosphere can connect to field lines in the magnetosheath, at least locally and for brief times, allowing the same population ofparticles to be observed on both sides of the boundary. In addition, a simple mathematical model is provided incorporating a time constant for the process re-supplying particles to the open flux tube. The observed data are satisfactorily reproduced using a time constant of 46 s, which is comparable to the half-bounce time of protons at this position. 相似文献
11.
A. Ranta H. Ranta T.J. Rosenberg U. Wedeken P. Stauning 《Planetary and Space Science》1983,31(12):1415-1434
We discuss the effects in ionospheric absorption of particle precipitation observed in the afternoon-early evening sector during substorms with onset in the midnight sector. All events considered here occurred during magnetically disturbed periods, Kp > 3. For many of the substorm events a smooth southward moving absorption bay is seen in the midnight and evening sectors about 1 h preceeding the onset. The magnetic pulsation activity is low during this preceding bay.
After substorm onset near magnetic midnight the precipitation region may expand with a sharp onset at the front towards the West in spatially confined regions at high and low L-values separately with about equal velocities. The observations are consistent with a model of westward expansion of the energetic electron precipitation in two regions, aligned parallel to the auroral oval, at high and low L-values of about L 6 and L 4.8.
The westward expanding absorption activity correlates well with local magnetic variations. In magnetic pulsations PiB events are seen at high latitudes simultaneously with the westward moving onsets while at low latitudes IPDP pulsations are observed during the active part of the absorption events. Later in the substorm event a slowly varying absorption event (SVA) is sometimes observed at the lower L-values, L 3–4. 相似文献
12.
Rickard Lundin 《Planetary and Space Science》1976,24(5):499-514
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
13.
Krzysztof Stasiewicz 《Planetary and Space Science》1985,33(6):591-596
The influence of low-frequency electrostatic turbulence on the flux of precipitating magnetospheric electrons is analyzed in the framework of the quasilinear kinetic equation. It is shown that an electron population in a turbulent region, with an electric field parallel to the ambient magnetic field, can be separated into two parts by introducing a pitch angle dependent runaway velocity vr(θ). Lower energy electrons with parallel velocity v∥ < vr are effectively scattered by plasma waves, so that they remain in the main population and are subjected to an anomalous transport equation. A distribution function f ∞ v?4 (or the particle flux vs energy J ∞ E?1) is established in this velocity range. Faster electrons with v∥ ? vr are freely accelerated by a parallel electric field, so that they contribute directly to hot electron fluxes which are observed at ionospheric altitudes. New expressions are derived for the magnetic-field aligned current and the electron energy flux implied by this model. These expressions agree well with empirical relations observed in auroral inverted-V structures. 相似文献
14.
As evidence for energy release in microflares, high time resolution observations of solar radio emission obtained with our “synchronous observation system of solar radio radiation with high time resolution at four frequencies (1.42, 2.13, 2.84 and 4.26 GHz)” from December 1989 to April 1993 are presented in this paper. The observed events include weak ms spikes, “spike-likes”, fast pulsations as well as two kinds of newly discovered fast fine structures, i.e., microwave type III bursts and microwave patch-like structures. A statistical study of the duration of fast fine structures has been made and on its basis the various types of phenomena are illustrated with actual examples. 相似文献
15.
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
16.
G. G. Bowman 《Planetary and Space Science》1960,2(4):214-218
The occurrence of the third (z-ray) component of the F2-trace on ionograms is investigated at high- and mid-latitudes. Diurnal variations show a systematic shift, with magnetic inclination, of the time of maximum occurrence. Seasonal variations show a winter maximum, and an inverse sunspot-cycle relationship exists. Maximum occurrence appears between a magnetic inclination of 70° and 80° with a fall-off either side.
Evidence is presented to suggest a z-ray association with “Spread-F” fronts, and a possible mechanism for the recording of the z-ray trace at the transmitter site is described. This involves longitudinal propagation of the o-mode at its normal reflection level, coupling at this point, and ultimate reflection for the z-ray mode as a result of sloping ionization contours belonging to “Spread-F” fronts extending in directions perpendicular to the magnetic meridian.
An association with V.L.F. emissions (“dawn-chorus”) is discussed. 相似文献
17.
On 13 August 1970, a sounding rocket carrying a high voltage electron accelerator and several electron detectors was launched from Wallops Island, Virginia. 16 msec long, 70 mA pulses were injected into the magnetosphere at pitch angles near 90°. In each pulse the electron energy was modulated between 35 and 43 keV. The electrons were trapped in the Earth's magnetic field and bounced between the northern and southern conjugate points with a period of ～0.65 sec and drifted eastward with a gradient-curvature drift velocity of ～765 m/sec. For about 90 seconds the rocket intercepted the returning echoes. Careful study of the rocket trajectory has allowed a partial space-time picture of an echo to be constructed. The bounce time and drift velocity observations are consistent with predictions based on internal magnetic field models with no electric fields. The flux has the spatial variations predicted by atmospheric scattering models at the southern conjugate point but is about a factor of 10 too low. After some injections delayed echoes are observed, apparently 40 keV electrons whose bounce time has been increased by ～75 msec, but with no change in their bounce averaged drift velocity. Study of detector response during gun pulses revealed three unexplained features: (1) a field aligned upward moving flux after downward injections; (2) a downward moving, time dependent, flux after injections at some upward pitch angles; (3) a lack of altitude (or atmospheric density) dependence on observed count rates. 相似文献
18.
We report observations of MeV heavy ions made with Explorer 45 in the earth's radiation belts during the 7-month period June–December 1972 when four major magnetic storms occurred. Significant fluxes of ions heavier than fluorine (i.e. with nuclear charge Z ? 9) were observed stably trapped in the interior of the radiation belts at L ～ 2–4. These energetic very heavy ions, were found to appear suddenly during the August 1972 magnetic storm period and their fluxes decayed during the following months on time scales typically several tens of days. Simultaneously, strong increases in the geomagnetically trapped MeV helium and CNO ion fluxes were observed, and the post-injection flux decay of these ions was found to be slower than that of the Z ? 9 ions. The relative enhancements in trapped fluxes during the storm increased with increasing ion mass and/or increasing ion energy. 相似文献
19.
Results from an ionoipheric founding rocket of the “mother-daugther” type, equipped with an 8 keV electron accelerator, is reported. The emphasis is on the results obtained from the three plasma probes which monitored both the electron- and the ion-population. It is shown that no significant increase of the electron density was observed during the beam injections. However, the electron temperature varied rapidly during these pulses. The influence of the vehicle charging on the measurements is also discussed. 相似文献
20.
对火星磁层中背阳面区来自电离层的Ｏ＋离子沿磁力线的密度和通量密度分布进行了理论研究．设火星的磁场由内禀磁场和感应磁场相叠加而成,结合不同的内禀磁矩条件进行了计算．结果表明：（１）随着火心距离的增大,火星磁层中Ｏ＋离子的密度和通量密度沿磁力线都呈现出下降趋势;（２）随着Ｚ坐标的增大,火星磁层中Ｏ＋离子的密度和通量密度先呈现出下降趋势,后又逐渐上升;（３）火星的内禀磁场越强,Ｏ＋离子的密度和通量密度沿磁力线下降得越快;（４）在火星磁尾一定距离处,Ｏ＋离子的密度和通量密度随磁矩的增大而减小．这样,可通过探测火星磁层中离子的密度和通量密度分布来确定火星内禀磁场的强弱 相似文献