摘要:

Processes which confine photoelectrons to the plasmasphere (e.g., collisional backscattering from the thermosphere and magnetic trapping due to pitch angle redistribution through Coulomb collisions in the plasmasphere) tend to increase the steady state photoelectron flux in the plasmasphere above the amplitude level that would otherwise have been attained. Theoretical calculations are presented of steady state photoelectron fluxes in the plasmasphere, for specified atmospheric and ionospheric conditions. (Observational plasma line intensity data for these conditions exist and will be compared elsewhere.) General features of the angular distribution are presented and compared with observations. The transparency of the plasmasphere and the backscattering properties of the thermosphere are investigated. The buildup effect due to collisional backscatter alone is calculated, and the combined buildup effect of pitch angle diffusion and backscatter is estimated. It is found that the inclusion of these effects increases the steady state photoelectron flux amplitude in the plasmasphere by about 50% over the value obtained when the buildup effects are neglected. The calculated steady state photoelectron fluxes in the plasmasphere are in good agreement with the available observations.

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00001

年代:1978

数据来源: WILEY

摘要:

An electrostatic analyzer on the electron accelerator of the Electron Echo 2 experiment showed that the electrons of the background plasma were heated to 10,000°K or more within 8 ms of the start of gun pulses. The degree of heating was dependent on the orientation of the rocket with respect to the magnetic field but was not measurably dependent on ambient electron density or neutral atmosphere density or on the pitch angle at which the 40‐keV electron beam was injected. This heating was also accompanied by an increase of plasma density. No evidence was found for an ion‐free region around the rocket during gun pulses. These observations show that significant amounts of ionization are taking place around the rocket. During part of the flight a two‐temperature electron distribution was found. It is believed that the high‐temperature part of these distributions represents secondaries produced by

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00016

年代:1978

数据来源: WILEY

摘要:

An attempt has been made to explain the departure of the observed hourly variation of phase height ofEregion reflections at 2.2 MHz from that expected of a simple undisturbed Chapman layer as the effect of vertical electromagnetic drift. Calculations show that a peak drift velocity ranging between the extreme limits 50.0 and 2.5 m/s located about 2 km below the electron density peak may account for the observed departure. Considering some related observational data it is suggested that the vertical drift velocity would be around 10–20 m/s, which is consistent with a value of α in the vicinity of 2–8 × 10

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00025

年代:1978

数据来源: WILEY

摘要:

The propagation of energetic solar protons of ≲1 MeV into the magnetosheath is investigated through three‐dimensional pitch angle distributions measured on Vela satellites. Distortions are observed in the magnetosheath as compared with isotropic or unidirectional distributions normally expected in inter‐planetary space. Two types of distortions are observed which are characterized by breaks in the distributions at μ00, where μ is the cosine of the pitch angle. The distributions in the magnetosheath are explained by a Liouville transformation, if particle motion across the bow shock and through the magnetosheath is assumed to be adiabatic. Whether μ0is positive or negative is determined by whether the satellite in the magnetosheath lies beyond or in front of the region of maximum magnetic field compression (or neck) in the magnetosheath, relative to the direction of the net flow of particles. The magnitude of μ0is a measure of the field ratio between neck and satellite. Scattering effects, which must occur at the bow shock and in the magnetosheath, only perturb the adiabatic propagation of the particles. The results show that one must be cautious in inferring the true interplanetary anisotropy from that measured in the magnetosheath. While the maxima and minima of the corresponding pitch angle distributions will be the same, the distributions can be vastly different, and both anisotropy and omnidirectional intensities significantly different, too. By corollary, the pitch angle distribution and anisotropy measured in the solar wind on a field line that intercepts the bow shock sunward of the earth will in general be different from that which would be measured in interplanetary space on a field line not connected to the bow shock; to first order the effect of the bow shock can be computed by treating the motion as

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00030

年代:1978

数据来源: WILEY

摘要:

As the Hawkeye 1 spacecraft crosses the plasmapause at high altitudes (R>3RE), a band of electric field noise is often detected in the frequency channels from 1.7 to 178 Hz. No corresponding magnetic field noise is detected, indicating that the noise is electrostatic (or at least quasi‐electrostatic), and the electric field is polarized perpendicular to the plasma density gradient. The noise is only detected when the scale length of the plasmapause is 0.1REor less, indicating that a large density gradient is required to produce the noise. These characteristics are all consistent with the interpretation that this noise consists of electrostatic waves excited by the drift mode instability. By using reasonable assumptions concerning the wavelengths of these waves the observed frequency spectrum can be explained as being due to Doppler shifts caused by spacecraft motion through the plasm

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00039

年代:1978

数据来源: WILEY

摘要:

Ground‐based recordings of broad‐band whistler mode signals propagating along the outer ‘surface’ of the plasmasphere, just beyond the region of steep plasmapause density gradients, exhibit a number of features that have not been observed in other field line regions. The features include extension of signal frequencies into the range ≃0.5–0.8 fHeq, where fHeqis the equatorial electron gyrofrequency of the path, and echoing or repeated propagation over the path at frequencies above 0.5 fHeq. The effects are frequently exhibited by tne ‘knee trace,’ the whistler component propagating just beyond the plasma‐pause in the low‐density or plasma trough region.The unusual features include VLF noise bands and bursts that are frequently triggered or ‘activated’ by knee whistler traces or echoes of knee traces. The noise bands and bursts tend to occur within the frequency range 0.4–0.8 fHeqand near the frequency of an amplitude peak in knee whistler trace activity. The wave activity is documented in VLF data from Eights, Antarctica (L≃4), for 1963 and 1965 and from Siple, Antarctica (L≃4.2), for 1973 through 1975. Certain features of the whistler and noise activity and of equatorial electron densities deduced from whistlers support earlier findings that the plasmapause equatorial radius may on occasion be irregular, varying by up to 1 REwithin the longitudinal viewing range (≃30°) of a whistler receiver. Propagation effects such as guidance along the outer plasmapause surface and coupling of wave energy into and out of the ionosphere are not yet well understood. The VLF noise effects are of a kind recently found to be associated with detectable bursts of electron precipitation into the nighttime lower ionosphere. Because of the special propagation and warm plasma effects associated with the plasmapause, that region appears to offer advantages for experiments on magnetospheric wave injection both fro

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00045

年代:1978

数据来源: WILEY

摘要:

Plasma wave measurements on the Helios 1 and 2 spacecraft have revealed the occurrence of electric field turbulence in the solar wind at frequencies between the electron and ion plasma frequencies. Wavelength measurements with the Imp 6 spacecraft now provide strong evidence that these waves are short‐wavelength ion acoustic waves which are Doppler‐shifted upward in frequency by the motion of the solar wind. Comparison of the Helios results with measurements from the earth‐orbiting Imp 6 and 8 spacecraft shows that the ion acoustic wave turbulence detected in interplanetary space has characteristics essentially identical to those of bursts of electrostatic turbulence generated by protons streaming into the solar wind from the earth's bow shock. In a few cases, enhanced ion acoustic wave intensities have been observed in direct association with abrupt increases in the anisotropy of the solar wind electron distribution. This relationship strongly suggests that the ion acoustic waves detected by Helios far from the earth are produced by an electron heat flux instability, as was suggested by Forslund. Possible related mechanisms which could explain the generation of ion acoustic waves by protons streaming into the solar wind from the earth's bow shock are also consi

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00058

年代:1978

数据来源: WILEY

摘要:

The occurrence of bidirectional anisotropies in low energy solar proton and electron events has been investigated in the period 1967–1973 by using data obtained from five satellites, viz., Explorer 34 and 41 and Vela 5B, 6A, and 6B. Some 16 observations of bidirectional distribution were detected in this time period, including the observation of bidirectionality in three solar electron events. The characteristics of two of these electron events are discussed in detail. The average duration over all events is 9 hours, implying a spatial scale of ≈0.13 AU, and the events show a strong correlation with the minimum of a Forbush decrease. The two maxima in the particle distributions are aligned with the interplanetary magnetic field. The origin of the bidirectional distributions is shown to be an interplanetary phenomenon rather than an effect of the bow shock. A magnetic configuration consisting of large‐scale loops in the interplanetary field (Gold bottle model) is suggested to account for the observations. The bidirectional flow can be produced by particle mirroring and by adiabatic expansion. The rarity of two‐way flow in solar electrons implies that special conditions must exist for its development. Our observations suggest that 1 out of 10 loop‐shaped coronal expulsions is detectable via two‐way cosmic ray particle flow near 1 AU. Bidirectional anisotropy observed in the event of August 4–5, 1972, in exact coincidence with the minimum of a striking Forbush decrease, suggests a shell1 of looped and well‐ordered field lines at the leading edge of the driver gas. The identification of this cavity, in which the galactic intensity is depressed, contradicts some aspects of published models of solar and galactic cosm

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00075

年代:1978

数据来源: WILEY

摘要:

Data from scanning photometers equipped with fixed interference filters selecting thePandRbranches of the N2+first negative (0–1) band were used to derive the temperature height profile through an auroral arc. The height of the arc was determined by two‐station triangulation techniques. The accuracy of the temperature determination is related to the relative intensity of the background aurora compared to the intensity of the arc. The need for a critical selection of the appropriate event to be analyzed and of the background to be subtracted is an important consideration in the analysis. In this particular example the most reliable part of the derived temperature profile lies between 105 and 140 km, and in this interval the temperatures agree well with the atmospheric temperature profile given by the U.S. Standard Atmosphere (1966) at 800°K exospheric temperature. No heating of the neutral atmosphere within the auroral arc was f

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00091

年代:1978

数据来源: WILEY

摘要:

Simple models are described which investigate the combined effects on solar wind He++of resonant and nonresonant acceleration by left‐hand transverse waves. The principal points are the following. (1) For a wide range of parameters, (υα– υp) at 1 AU is close to the effective phase speed of the left‐hand waves. (2) The most important factor in determining υα/υpat 1 AU is whether the high‐frequency left‐hand waves are predominantly outward propagating, inward propagating, or a mix of both. The resonant acceleration may be more important than the effects of heating or stream‐stream interactions. (3) Reasonable values of υα/υpat the sun (and ofnα/npat 1 AU) are obtained for a power law index α ≅ 1.5 in the wave power spectrum if the effective phase speed of the resonant waves near the sun is not small in comparison to the Alfvén speed there. This requires a substantial level of high‐frequency power in outward going waves at the sun, which cannot come from heat‐conduction‐driven instabilities. (4) The present models do not allow one to decide whether the coronal He++abundance is greater or less than that at 1 AU. (5) Some of the models show a positive correlation betweennα/npand υpat 1 AU, roughly as has been observed. (6) The models suggest that variations innα/npat 1 AU can result from variations in the wave properties near the sun and not necessarily from variations in the coronal abundance. (7) Some models indicate that (υα/υp) may decrease with increasing r in the vicinity of 1 AU. (8) The resonant acceleration is more efficient than Coulomb friction in the sense that it does not exhibit a runaway effect. (9) Observations of minor species may be used to deduce wave properties a

ISSN:0148-0227    

DOI:10.1029/JA083iA01p00097

年代:1978

数据来源: WILEY