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1.
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
2.
Rocket measurements of lower ionosphere electron density by propagation characteristics of VLF waves
The electron density profile in the lower ionosphere was determined from the right- and left-handed circularly polarized wave fields of a 40 kHz ground based signal observed by means of a rocket born receiver. Estimation of the electron density profile from 70 km up to 100 km was made under the condition for the values calculated by the full wave analysis to agree with the observed values. Results are presented for two rockets launched soon after sunset. 相似文献
3.
R.N. Srivastava 《Planetary and Space Science》1974,22(11):1545-1564
Comparison of the low altitude polar orbiting Injun 5 Satellite data with the ground VLF data has revealed that there is a definite scarcity of VLF/ELF emissions at the ground level compared with the extent to which they are present at or above the auroral altitudes. Reasons for this have been investigated by performing ray path computations for whistler mode VLF propagation in an inhomogeneous and anisotropic medium, such as the magnetosphere and the ionosphere. Based on wave normal computations in the lower ionosphere, it has been found that many of the near-auroral zone VLF/ELF events are frequently either reflected from, or heavily attenuated in, the lower ionosphere. Besides collisional loss, severe attenuation of VLF signals in the lower ionosphere is also caused by the divergence of ray paths from the vertical (spatial attenuation). Cone of wave normal angles for the wave, within which VLF/ ELF signals are permitted to reach the ground, has been established. Wave normals lying outside this transmission cone are reflected from the lower ionosphere and do not find exit to the Earth-ionosphere cavity. Computations for VLF signals produced at auroral zone distances in the equatorial plane of the magnetosphere indicates that these signals are more or less trapped in the magnetosphere at altitudes > 1RE. 相似文献
4.
Eddy current torques,air torques,and the spin decay of cylindrical rocket bodies in orbit 总被引：1，自引：0，他引：1
This paper considers the torques causing spin decay in cylindrical rocket bodies in orbit. Eddy current torques, due to the Earth's magnetic field, are estimated using Smith's (1962) model—a hollow cylindrical conducting shell, tumbling about a transverse axis. Air torques are estimated by numerical integration of aerodynamic moments over the rocket surface. It is shown that for Cosmos rockets, 7.4 m long and 2.4 m in diameter, eddy current torques outweigh air torques by several orders of magnitude at altitudes near 500 km, and that they are dominant at altitudes down to 160 km. Visual observations of several such rockets illustrate a variation of spin decay time with altitude which supports this conclusion. The same observations suggest that a few Cosmos rockets may be special cases, different from the rest in construction. 相似文献
5.
Several Nike-Apache rockets with Lang muir probe payloads were launched from Thumba (India) to study the disturbances produced by a moving rocket. The rockets were launched during different times of the day and night. It was found that low frequency ion plasma oscillations of the order of 1 KHz frequency were observed in the altitude region 145 to 200 km. This altitude region corresponds to the rocket apogee region where the rocket velocity is subsonic. The amplitude of the fluctuations was about 1 to 2% and was found to be dependant on rocket velocity electron density in the ambient medium, rocket spin and probe voltage. It was noticed that in the case of Centaure and Petrel rockets such types of oscillations were not observed. The Nike-Apache rockets are made of aluminium while Centaure and Petrel rockets are made of stainless steel. 相似文献
6.
A double-probe electric field detector and two spatially separated fixed-bias Langmuir probes were flown on a Taurus-Tomahawk sounding rocket launched from Poker Flat Research Range in March 1982. Interesting wave data have been obtained from about 10s of the downleg portion of the flight during which the rocket passed through the auroral electrojet. Here the electric field receiver and both density fluctuation (δn/n) receivers responded to a broad band of turbulence centered at 105 km altitude and at frequencies generally below 4 kHz. Closer examination of the two (δn/n) turbulent waveforms reveals that they are correlated, and from the phase difference between the two signals, the phase velocity of the waves in the rocket reference frame is inferred. The magnitude and direction of the observed phase velocity are consistent either with waves which travel at the ion sound speed (Cs) or with waves which travel at the electron drift velocity. The observed phase velocity varies by about 50% over a 5 km altitude range—an effect which probably results from shear in the zonal neutral wind, although unfortunately no simultaneous neutral wind measurements exist to confirm this. 相似文献
7.
Examination of thermal plasma data obtained by low-altitude satellite measurements indicates that the intersection of the cusp in the dayside magnetosphere with the topside ionosphere creates a distinct plasma geometry at low altitudes. This region consists of one or two plasma discontinuities with steep boundaries. As a result of the plasma structuring in the cusp which commonly takes place in the winter hemisphere, the propagation of compressional surface MHD waves is supported. This point is illustrated by an analysis of the polarization state of compressional surface MHD waves propagating along a plasma layer with thickness a and ambient magnetic field B0 parallel to the interfaces. The results obtained are applicable to the case of a single interface, which is derived in the limit a → ∞. In the general case the polarization of the compressional surface MHD waves in the plane transverse to the magnetic field B0 is elliptical. This feature of the polarization state of the compressional surface modes does not follow from the former analysis by Edwin and Roberts (1982, Solar Phys. 76, 239) for a magnetic slab, because the disturbance components parallel to the interfaces and perpendicular to the magnetic field B0 have not been examined. Although the absence of these components does not prove to be essential for deriving the exact dispersion equation for arbitrary wave directions of the surface modes, they must be included when considering polarization states. The surface mode polarization in the plasma layer changes its sense three times: at interfaces X = 0 and X = a and in the middle plane X = a/2. For the symmetrical (sausage) mode the wave disturbance component bn transverse (normal) to the interfaces becomes zero in the middle plane; for the asymmetrical (kink) mode, the component bt parallel to the interfaces and transverse to the ambient magnetic field is zeroed in the same plane. For a moving observer such as a satellite the polarization patterns which might be recorded change, depending on the velocity of the observer and the angles at which the layered cusp is traversed. An essential feature in the polarization of the compressional surface MHD modes is the presence of jumps in the magnetic disturbance component bt at the interfaces. These jumps disappear only for propagation along the ambient magnetic field. In this particular case the component bt vanishes and then the surface modes are undistinguishable from the body modes. 相似文献
8.
Employing the Haselgrove ray tracing equations and a diffusive equilibrium model of the ionosphere, the propagation characteristics of hook whistlers recorded at low-latitude ground station Varanasi (geomag. lat., 16°6′.N) are discussed. It is shown that the two traces of the hook whistlers are caused by the VLF waves radiated from the return stroke of a lightning discharge which after penetrating the ionosphere at two different entry points, propagated to the opposite hemisphere in the whistler mode and were received at 16 geomagnetic latitude. Further the crossing of ray paths for the same frequency leads to the explanation of the hook whistler. The lower and higher cut-off frequencies are explained in terms of their deviating away from the bunch of the recorded whistler waves and crossing of ray paths for the same frequency. 相似文献
9.
M. V. Samokhin 《Astrophysics and Space Science》1976,44(1):141-150
The distributions of the current and the neutral winds driven by the electric field of convection are calculated in the dynamo-region of the ionosphere. At high latitudes the convection field drives the current and wind systems which consist of two cells with the centres at about 6 and 18 hours LT. In the northern hemisphere in the dawn cells winds and currents are clockwise, in the dusk cells they are counterclockwise. The appearance of the wind system shows that the upper atmosphere moves in the direction inverse to the displacement of the ionospheric ends of the magnetic flux tubes taking part in the convection. In the disturbed conditions the calculated wind system has the directions and velocities of the winds which are in a satisfactory agreement with the data of the irregularity drifts in the lower ionosphere in the winter season. 相似文献
10.
The three-dimensional current system over an enhanced conductivity strip identified with an auroral arc is calculated for the case of the magnetospheric plasma convection across this strip. The strip produces a stationary Alfvén wave which propagates along magnetic field lines and is carried simultaneously by the convecting plasma. The Alfvén wave generation corresponds to an appearance of field-aligned currents over the arc. The three-dimensional current system generated over the arc is studied, taking into account reflection of the waves from the ionosphere of the opposite hemisphere. The correspondence of the theory with the experimental results is found. 相似文献
11.
M.K. Andrews 《Planetary and Space Science》1977,25(10):957-966
During a long series of recordings of the Doppler shift of signals from NLK, Seattle, which have propagated in ducts in the whistler mode, a number of occasions have been noted where the duct has been acted on by the electric field of micropulsation events in the Pc4–5 range. Large oscillations are produced in the Doppler shift of the received VLF signal.It is shown that the field line has an antinode of motion in the equatorial plane, and that the Doppler shift is responding almost entirely to the radial component of the duct motion. The latter enables a comparison to be made between the magnetic disturbance in the magnetosphere and that seen on the ground. Some support is given to the prediction of Hughes (1974) and Inoue (1973) that the magnetospheric disturbance vector when seen on the ground is rotated 90° by the currents induced in the ionosphere. Models of the oscillating field line enable an estimate to be made of the azimuthal component of the electric field in the equatorial plane. This is typically . The model also predicts the north-south magnetic field strength of the transverse standing wave at the base of the magnetosphere, and this value may be compared with that seen on the ground. Values of the order 1–2 times the ground H-component or 5–10 times the ground D-component were found. 相似文献
12.
H. B. Liemohn 《Astrophysics and Space Science》1973,20(2):417-429
The magnetosphere of Jupiter has been the subject of extensive research in recent years due to its detectable radio emissions. Observations in the decimetric radio band have been particular helpful in ascertaining the general shape of the Jovian magnetic field, which is currently believed to be a dipole with minor perturbations. Although there is no direct evidence for thermal plasma in the magnetosphere of Jupiter, theoretical considerations about the physical processes that must occur in the ionosphere and magnetosphere surrounding Jupiter have lead to estimates of the thermal plasma distribution. These models of the Jovian magnetic field and thermal plasma distribution, specify the characteristic plasma and cyclotron frequencies in the magnetosplasma and thereby provide a basis for estimating thelocal electromagnetic and hydromagnetic noise around Jupiter. Spatial analogs of the well-known Clemmow-Mullaly-Allis (CMA) diagrams have been constructed to identify the loci of electron and ion resonances and cutoffs for the different field and plasma models. Regions of reflection, mode coupling, and probable amplification are readily identified. The corresponding radio noise properties may be estimated qualitatively on the basis of these various electromagnetic and hydromagnetic wave mode regions. Frequency bands and regions of intense natural noise may be estimated. On the basis of the models considered, the radio noise properties around Jupiter are quite different from those encountered in the magnetosphere around the Earth. Wave particle interactions are largely confined to the immediate vicinity of the zenographic equatorial plane and guided propagation from one hemisphere to the other apparently does not occur, except for hydromagnetic modes of propagation. The characteristics of these local signals are indicative of the physical processes occurring in the Jovian magnetosphere. Thus, as a remote sensing tool, their observation will be a vital asset in the exploration of Jupiter. 相似文献
13.
Making use of currently available theory of wave absorption, an attempt has been made to estimate the refractive indices and absorption coefficients for different wave frequencies during day and night times in the Jovian ionosphere. The results obtained have striking similarity with the corresponding results in the case of the Earth's ionosphere. It is concluded that VLF signals can be observed more easily during night times. 相似文献
14.
Nobuki Kawashima Susumu Sasaki Osamu Kaneko Akira Yamori Ryo Okamura Shoichi Okamura 《Planetary and Space Science》1978,26(4):367-373
A controlled active experiment was performed by a plasma gun on-board a rocket to study the plasma stream across the magnetic field in space. A mother and daughter system was employed. An 8 kV 0.8 μF (25 J) capacitor bank on the daughter rocket was discharged every 12 s and about 1016 ion and electron pairs were ejected. A plasma signal was detected on the electron temperature probe. The propagation speed of the plasma stream is estimated to be 106 cm/s, considerably lower than that obtained in the prelaunch test. The amplitude of the plasma signal decays as the inverse square of the mutual distance between the mother and daughter rockets and this decay is much slower than the free streaming. The importance of the geomagnetic field on the plasma propagation in space is discussed. 相似文献
15.
Venus Express observations of ULF and ELF waves in the Venus ionosphere: Wave properties and sources
Electrical activity in a planetary atmosphere enables chemical reactions that are not possible under conditions of local thermodynamic equilibrium. In both the Venus and terrestrial atmospheres, lightning forms nitric oxide. Despite the existence of an inventory of NO at Venus like the Earth’s, and despite observations of the signals expected from lightning at optical, VLF, and ELF frequencies, the existence of Venus lightning still is met with some skepticism. The Venus Express mission was equipped with a fluxgate magnetometer gradiometer system sampling at rates as high as 128 Hz, and making measurements as low as 200 km altitude above the north polar regions of Venus. However, significant noise levels are present on the Venus Express spacecraft. Cleaning techniques have been developed to remove spacecraft interference at DC, ULF, and ELF frequencies, revealing two types of electromagnetic waves, a transverse right-handed guided mode, and a linearly polarized compressional mode. The propagation of both types of signals is sensitive to the magnetic field in ways consistent with propagation from a distant source to the spacecraft. The linearly polarized compressional waves generally are at lower frequencies than the right-handed transverse waves. They appear to be crossing the usually horizontal magnetic field. At higher frequencies above the lower hybrid frequency, waves cannot enter the ionosphere from below when the field is horizontal. The arrival of signals at the spacecraft is controlled by the orientation of the magnetic field. When the field dips into the atmosphere, the higher frequency guided mode above the lower hybrid frequency can enter the ionosphere by propagating along the magnetic field in the whistler mode. These properties are illustrated with examples from five orbits during Venus Express’ first year in orbit. These properties observed are consistent with the linearly polarized compressional waves being produced at the solar wind interface and the transverse guided waves being produced in the atmosphere. 相似文献
16.
Recent observational evidence for magnetic field direction effects on helioseismic signals in sunspot penumbrae is suggestive of magnetohydrodynamic (MHD) mode conversion occurring at lower levels. This possibility is explored using wave mechanical and ray theory in a model of the Sun's surface layers permeated by uniform inclined magnetic field. It is found that fast-to-slow conversion near the equipartition depth at which the sound and Alfvén speeds coincide can indeed greatly enhance the atmospheric acoustic signal at heights observed by Solar and Heliospheric Observatory/Michelson Doppler Imager and other helioseismic instruments, but that this effect depends crucially on the wave attack angle , i.e. the angle between the wavevector and the magnetic field at the conversion/transmission depth. A major consequence of this insight is that the magnetic field acts as a filter, preferentially allowing through acoustic signal from a narrow range of incident directions. This is potentially testable by observation. 相似文献
17.
Previously developed solutions for pure toroidal mode Alfvén waves with finite ionosphere conductivities are modified to apply both inside and outside the plasmapause.Detailed diagrams are provided to illustrate the effect of realistic ionosphere conductances on the wave-forms. As well as graphs of wave-period, these include: (a) half-wave solutions showing the effect of dipole field distortion and consequent enhancement of ionosphere electric fields; (b) half-wave solutions with low damping that are symmetric and asymmetric about the equatorial plane; (c) highly-damped half-wave and quarter-wave solutions with wave admittance at the ionosphere nearly equal to the ionosphere conductance; (d) a quarter-wave solution with low damping that has a “near-node” of electric field at one ionosphere and an antinode of electric field at the other. 相似文献
18.
电离层从猜想到证实完全是无线电技术发展的结果。通过地面无线电探测和火箭、卫星的空间探测、证实了Ｃｈａｐｍａｎ的理论。由于太阳紫外线，Ｘ射线辐射致使高空上层大气电离。电离层介质是电子、正负离子和中性粒子全体的混合物。它们构成了地磁场中磁离子介质。本文根据磁离子理论，研究了电离层中等离子体的频率特性，从而解释了Ｄ、Ｅ、Ｆ１和Ｆ２层的电波反射特性。最后计算了陕西天文台至云南天文台电离层波导的传播时延，获得了有意义的结果。 相似文献
19.
Extreme low frequency electromagnetic waves have been observed below the F peak in the equatorial ionosphere by instruments onboard OGO-6. Electrostatic wave observations indicate that the steep gradient was unstable to the process which causes equatorial spread F above the region where the electromagnetic waves were observed. The data are very similar to observations near the polar cusp and give further evidence that ELF waves are excluded from regions of rapid and irregular density increases. Low level electromagnetic waves with similar properties were occasionally observed on the nightside by the OVI-17 electric field sensor and may be plasmaspheric hiss which has propagated to low altitude. 相似文献
20.
The downward propagation of ELF waves (100–700 Hz) in the ionosphere is studied by means of a generalised multiple-reflection full-wave method. It is shown that for the production of an ion cutoff whistler the incident wave-normal must point inwards (equatorwards) with respect to the vertical, the ion cutoff whistler conversion coefficient RRL being a maximum when the reflected wave normal lies close to the geomagnetic field direction at the crossover level.For a low frequency cutoff of ELF noise to exist, the incident wave-normals at the crossover level must lie outside a ‘cone of penetration’ of ~40° semi-vertical angle, whose axis coincides with the geomagnetic field line. For propagation in the magnetic meridian plane, total reflection of downgoing whistlers is obtained either for large outward (poleward) incident angles, with reflection heights generally above the crossover level and possibly even above the gyrofrequency level, or else for inward (equatorward) wave-normal directions, in which case the reflection process usually occurs below the crossover level, and involves an R to L mode conversion on the downgoing path.Analysis of a scatter plot of the lower cutoff frequencies of ELF noise as a function of altitude and latitude shows that widely varying abundances must be postulated at all latitudes in order to explain the observations. 相似文献