摘要:

Average characteristics of solar wind electron velocity distributions as well as the range and nature of their variations are presented. The measured distributions are generally symmetric about the heat flux direction and are adequately parameterized by the superposition of a nearly bi‐Maxwellian function which characterizes the low‐energy electrons and a bi‐Maxwellian function which characterizes a distinct, ubiquitous component of higher‐energy electrons. An alternate self‐consistent description of the higher‐energy component is presented in terms of an unbound population of hot electrons with energy greater than some breakpoint energy of ≃60 V. The largest‐scale parameter variations appear to come most often in association with high‐speed streams. The salient electron parameter variations associated with these structures are presented and discussed. The mechanism by which interplanetary electrons conduct heat is convection of the hot component relative to the bulk speed. Arguments are presented which favor the local regulation of the solar wind

ISSN:0148-0227    

DOI:10.1029/JA080i031p04181

年代:1975

数据来源: WILEY

摘要:

The linear dispersion properties of three electron heat flux plasma instabilities are studied in detail by using parameters appropriate to average values in the solar wind at 1 AU. Among the (fast) magnetosonic, Alfvén, and whistler instabilities the first one appears most likely to make a significant contribution to the regulation of the heat flux

ISSN:0148-0227    

DOI:10.1029/JA080i031p04197

年代:1975

数据来源: WILEY

摘要:

An algorithm is presented for predicting the ground‐basedDstindex solely from a knowledge of the velocity and density of the solar wind and the north‐south solar magnetospheric component of the interplanetary magnetic field. The three key elements of this model are an adjustment for solar wind dynamic pressure, an injection rate linearly proportional to the dawn‐to‐dusk component of the interplanetary electric field which is zero for electric fields below 0.5 mV m−1, and an exponential decay rate of the ring current with anefolding time of 7.7 hours. The algorithm is used to predict theDstsignature of seven geomagnetic storm intervals in 1967 and 1968. In addition to being quite successful, considering the simplicity of the model, the algorithm pinpoints the causes of various types of storm behavior. A main phase is initiated whenever the dawn‐to‐dusk solar magnetospheric component of the interplanetary electric field becomes large and positive. It is preceded by an initial phase of increasedDstif the solar wind dynamic pressure increases suddenly prior to the main phase. The recovery phase is initiated when the injection rate governed by the interplanetary electric field drops below the ring current decay rate associated with the ring current strength built up during the main phase. Variable recovery rates are generally due to additional injection during the recovery phase. This one algorithm accounts for magnetospheric behavior at quiet and at disturbed times and seems capable of predicting the behavior ofDstduring even the larg

ISSN:0148-0227    

DOI:10.1029/JA080i031p04204

年代:1975

数据来源: WILEY

摘要:

An analytic theory is developed for both the steady state and the time‐dependent electric and magnetic fields inside the moon and its downstream cavity for interplanetary electromagnetic field fluctuations incident at arbitrary angles to the cavity axis. The moon model has an electrical conductivity, electrical permittivity, and magnetic permeability which vary arbitrarily with radius. The cavity downstream of the moon in the solar wind is assumed to be an infinitely long nonconducting cylinder. If the interplanetary field fluctuations propagate parallel to the cavity, the far cavity field is a single cylindrical transverse electric mode propagating downstream with the same frequency, wavelength, and phase velocity as the interplanetary field. The far cavity field is the result of a forced surface wave on the cylindrical boundary of the void. When the interplanetary fluctuations are incident at an arbitrary angle to the cavity axis, the far cavity field is a superposition of an infinite number of cylindrical TE (transverse electric) and TM (transverse magnetic) modes. Each of these modes is a surface wave with the same frequency and downstream phase velocity (the ratio of the angular frequency to the magnitude of the component of the interplanetary wave vector parallel to the cavity axis) as the incident interplanetary field. If the magnetic perturbation vector of the incident wave is normal to the cavity axis, the far cavity field is a linear combination of cylindrical TE and TM modes for arbitrary angles of incidence. However, if the interplanetary electric field fluctuation is normal to the axis of the void, the far cavity field is pure TE independent of the incidence angle. Resonances can occur in the far cavity TE and TM forced surface waves if the apparent velocity of the interplanetary wave parallel to the void axis, i.e., the downstream phase velocity, coincides with one of the characteristic TE or TM wave guide speeds of the circular cylindrical void for waves of the same frequency as the interplanetary radiation. When the interplanetary waves travel parallel to the void axis, their downstream and actual phase velocities coincide; these phase speeds are smaller than the velocity of light in vacuum,c, so that no resonances in the far cavity field are possible, since characteristic wave guide phase velocities are greater thanc. Particular TE and TM modes may be absent from the far cavity field for certain incidence angles and frequencies of the interplanetary radiation. At normal incidence the far cavity behaves as a forced electromagnetic oscillator. At frequencies greater than 50 and 105 Hz, for the TE and TM modes, respectively, the cavity is a cylindrical wave guide for electromagnetic field perturbations associated with the moon. For frequencies less than 50 Hz the cavity field perturbations due to the presence of the moon are attenuated downstream of the moo

ISSN:0148-0227    

DOI:10.1029/JA080i031p04215

年代:1975

数据来源: WILEY

摘要:

A model for unsteady interactions between solar wind disturbances and the magnetosphere associated with the southward shift of the solar wind magnetic field during the growth phase of substorms is presented. It is emphasized that the presence of the solar wind electric current relating to the southward turning of the magnetic field and its interaction with the magnetosphere are essential in describing the transient process that generates the large‐scale magnetospheric convection. Conceptual discussion on the stress generation due to the interaction in the outermost part of the magnetosphere and its transport into the inner magnetosphere and the high‐latitude ionosphere are given. In comparison with the fast transient process, for instance, ssc* of magnetic storms, the slow magnetosonic wave will play an essential role in the slow process, such as the early stage of the growth phase. By using the equivalent circuit model along with the above consideration the time response of the magnetosphere‐ionosphere current system for this interaction is examined. The results indicate that a coupling of a rather large capacitance for the slow mode, in comparison with that for the Alfvén mode, with the ionospheric resistance can yield a long time delay for the saturation of the ionospheric c

ISSN:0148-0227    

DOI:10.1029/JA080i031p04230

年代:1975

数据来源: WILEY

摘要:

Three years of Imp 5 data show that the magnetopause layer of energetic electrons was present during 227 of 230 orbits over this period and extends along the magnetopause from geomagnetic latitudes as low as 40° to latitudes corresponding to the polar cap. It also exists at the boundary between the magnetosheath and the polar cusp region. The data show that the integral energy spectrum of these electrons (Ee>18 keV) varies greatly with the planetaryKpindex and hardens with increasingKpvalues. The average spectrum can be represented by a power lawJ(>E) ∝E−α, where α = 1.94 ± 0.19. The intensity of the magnetopause layer electrons increases with increasingKpvalues and also has a weak dependence on the magnitude of the north‐south component of the interplanetary magnetic field. The energy density of the energetic electrons in this layer is of the order of 10

ISSN:0148-0227    

DOI:10.1029/JA080i031p04237

年代:1975

数据来源: WILEY

摘要:

There exist magnetic fields in which particles bouncing between mirror points experience no net first‐order guiding center drift. In such fields, even though the instantaneous gradient and curvature drifts are not zero, their total effect integrated over any bounce period vanishes, so that particles merely wobble back and forth around fixed field lines. A class of two‐dimensional drift‐free fields, somewhat resembling the configuration found in the geomagnetic tail, is described; several proofs of the drift‐free property are given, including some that suggest that the property of vanishing net drift might extend to nonadiabatic orbits. A general criterion for identifying drift‐free fields is developed, and a case of motion in a nearly drift‐free field is also investigated. The theory is applied to the plasma sheet in the earth's magnetotail, and observational evidence is presented suggesting that the magnetic field there indeed approaches a drift‐free

ISSN:0148-0227    

DOI:10.1029/JA080i031p04244

年代:1975

数据来源: WILEY

摘要:

In a recent experiment, discrete VLF emissions from the magnetosphere were triggered by a transmitter at Siple Station in Antarctica. Spectrograms of these signals as received at the conjugate point, Roberval, Quebec, showed changes in slope, entrainments, and cutoffs at frequencies (several kilohertz) close to the harmonic induction lines from the local 60‐Hz power system. This observation led to the suggestion that harmonic radiation from the power system enters the magnetosphere and interacts with the triggered emissions. New evidence supporting this suggestion has been found in spectrograms of simultaneous recordings made at Roberval and at Siple Station in Antarctica. It is shown that line radiation, near harmonics of 60 Hz, travels along the earth's magnetic field in the whistler mode and is received in the conjugate hemisphere at Siple Station. Echoing of the line radiation between Siple and Roberval is often observed. The magnetospheric lines are usually shifted in frequency by 20–30 Hz with respect to the adjacent induction line, but their spacings are near 120 Hz. They may trigger and cut off emissions as do signals from VLF transmitters. Occasionally, magnetospheric lines are seen with spacings of only 20–30 Hz. This smaller frequency separation and the frequency shift of other lines spaced 120 Hz apart are related to the positive frequency offset of emissions triggered by VLF signals from the Omega navigation transmitters. Harmonic lines of reasonable amplitude (∼10−3γ) are shown to enhance significantly the precipitation of 2‐keV electrons over the eastern parts of the American continents nearL∼ 4. Some mid‐latitude hiss bands appear to consist of sets of magnetospheric lines and their associated tri

ISSN:0148-0227    

DOI:10.1029/JA080i031p04249

年代:1975

数据来源: WILEY

摘要:

Naturally occurring noise bands near the electron plasma frequency are frequently detected by the University of Iowa plasma wave experiment on the Imp 6 satellite in the region from just inside the plasmapause to radial distances of about 10REin the outer magnetosphere. The electric field strength of these noise bands is usually small with typical broad band electric field strengths of about 2 µV m−1. A magnetic field has been detected only in a few unusually intense cases, and in these cases the magnetic field energy density is several orders of magnitude smaller than the electric field energy density. The bands are observed at all magnetic latitudes covered by the Imp 6 orbit (|λm| ≲ 45°) and appear to be a permanent feature of the outer magnetosphere. They are found at all local times and occur least frequently in the quadrant from 18 to 24 hours. The bands appear to consist of two distinct spectral types which we have called diffuse and narrow band. In both types the center frequency of the noise band is bounded by consecutive harmonics of the electron gyrofrequency, and these noise bands occur most often between harmonics that are near the local electron plasma frequency. They appear to merge continuously into two other types of plasma wave emissions that are found in dissimilar regions of the magnetosphere (upper hybrid resonance noise, also called region 3 noise, inside the plasmasphere and (n+ ½)fgharmonics in the outer magnetosphere). It is suggested that this smooth merging is caused by changes in the plasma wave dispersion relation that occur as the spacecraft moves from the cold plasma within the plasmasphere into the warm non‐Maxwellian plasma found in the outer magn

ISSN:0148-0227    

DOI:10.1029/JA080i031p04259

年代:1975

数据来源: WILEY

摘要:

Narrow band VLF signals with a structure similar to that of chorus were observed on a rocket payload launched from ESRANGE (European Space Range) near Kiruna, Sweden. The payload penetrated a proton glow aurora and flew over an auroral arc. It is shown that the signals which occurred in the frequency range 3.0–3.4 kHz probably are generated in the lower ionosphere, and the high‐frequency two‐stream instability developed by K. Lee et al. (1971) is suggested as the generation mech

ISSN:0148-0227    

DOI:10.1029/JA080i031p04272

年代:1975

数据来源: WILEY