摘要:

On February 13, 1967, a class 3B solar flare occurred at 20°N, 10°W. The resultant disturbance in the solar wind was observed by the Los Alamos plasma probe on Vela 3A and the Ames Research Center magnetometer on Explorer 33. The initial discontinuity in the solar wind was identified as a shock. The normal to the shock made an angle of 60° with the plane of the ecliptic. This extreme angle of tipping indicates that the shock from this flare did not propagate spherically from the sun as described by simple theory. Nine hours after the shock passed, plasma containing 22% helium was observed. Since the solar wind normally contains 4% helium, this observation adds to the increasing body of evidence that flares occur in regions relatively rich in helium. The velocity of the solar wind continued to increase after the helium plasma passed, i.e., at 1 AU the helium‐enriched material was still being propelled from behind. This observation is evidence that the plasma continued to be accelerated at the sun for an extended period of time after the flash phase of the f

ISSN:0148-0227    

DOI:10.1029/JA075i001p00001

年代:1970

数据来源: WILEY

摘要:

Associated with the large heat conduction in the solar wind is a skewing of the ion and electron distribution functions. It is shown that this collisional skewing of the electron distribution function can linearly excite collisionless ion‐acoustic, electrostatic ion cyclotron, magnetoacoustic, and ion cyclotron waves in the steady‐state solar wind even though the net equilibrium current parallel to B is zero. The initial growth rates for these unstable waves are derived, and the effectiveness of the wave‐particle interactions in heating the ions and in altering the thermal and electrical conductivities is disc

ISSN:0148-0227    

DOI:10.1029/JA075i001p00017

年代:1970

数据来源: WILEY

摘要:

Solar electrons of energyEe≳ 50 kev are used as test particles for studying electric and magnetic fields in the distant magnetotail of the earth. During the prolonged solar electron event November 10‐22, 1967 (J. A. Van Allen and N. F. Ness, 1969), simultaneous observations were made with the earth‐orbiting satellite Explorer 33 in interplanetary space and with the moon‐orbiting satellite Explorer 35 as the latter crossed the magnetotail. On the basis of the fact that the intensity of electrons was nearly identical at successive pairs of observational points during a wide range of geomagnetic conditions, it is inferred (a) that|∫A′BE·ds|≤1.5kilovoltswhere E is the vector electric field, from any cause, at a vector element ds of the trajectory of the particle and the line integral is taken along trajectories from source pointsA′outside the magnetosphere to a succession of pointsBacross the magnetotail at about 64RE(earth radii) downstream; and (b) that, by using (a), data from Van Allen and Ness, and observations of the very short delay time (±100 sec) in access of solar electrons into the central part of the magnetotail (impulsive event of August 14, 1968, as an example), solar electrons enter the magnetotail at downstream distances between 64 and 900RE(cf. R. P. Lin and K. A. Anderson, 1966). Otherwise stated, it appears that the magnetic topology of the distant magnetotail is an ‘open one’ (dynamic interconnection to the interplanetary field) and that there are no closed electrical equipotential surfaces beyond 64RE. This evidence supports the idea that the motional electromotive force that results from the movement of the interplanetary magnetic field with respect to the earth plays an essential role in magnetospheric physics, e.g., in driving magnetospheric convection, electrical currents in the

ISSN:0148-0227    

DOI:10.1029/JA075i001p00029

年代:1970

数据来源: WILEY

摘要:

Low‐altitude, high‐latitude observations of 0.52≤Ep≤4 Mev protons by the University of Iowa/NASA satellite Injun 4 are presented for three solar proton events having maximum intensities on January 20, May 30, and June 23, 1966. Only weak magnetic storms were associated with these events. A substantial body of new data is given on the magnetic local time (MLT) dependence of the geomagnetic cutoffs and the counting rate versus invariant latitude profiles from 0600 to 1300 hours and 1800 to 2200 hours for low‐energy protons moving approximately normal to the local magnetic field. The observed cutoffs consist of two sets, one is independent of MLT at 66.5° invariant latitude and the upper set has marked local‐time dependence, going from 68° at 0600 hours MLT to ∼75° at 1000 hours and back to 68° by 1900 hours. Pitch‐angle distributions were not actually measured, but an interpretation based on pitch‐angle anisotropies is suggested which is consistent with the quasi‐trapping suggested by Taylor and others and experimentally observed by Paulikas, Blake, and Freden. The results so interpreted yield information on the extent of the quasi‐trapped region over an extensive range of local time. The boundaries are qualitatively in agreement w

ISSN:0148-0227    

DOI:10.1029/JA075i001p00039

年代:1970

数据来源: WILEY

摘要:

The plasmapause position has been measured quite well by the light ion mass spectrometer aboard OGO 5, which measures the concentrations of H+, He+, and O+ions as a function ofLand local time. The influence of magnetic activity on this plasmapause position has been studied for the local‐time regions at 1000±2 hours and 0200±2 hours. The plasmapause location shows a general decrease in radius with increasing activity in both regions. The time lag between the onset of magnetic activity and the change in plasmapause radius is found to be about 2 to 6 hours for the 0200 local‐time region. However, the time lag for the 1000 local‐time region is not well defined, although the 6‐hour lag time seemed to fit some of the cases better than the 12‐ or 24‐hour periods that were examined. By using the 2‐ to 6‐hour response time, the plasmapause density profiles in the 0200 local‐time region were grouped according to magnetic activity. This grouping displays the typical plasmapause reaction in this local‐time region to increasing magnetic activity with the knee position moving to lowerLvalues, the sharpness of the knee increasing, and the total concentration levels inside and outside the knee remaining approximately the same at 10³ ions/cm³ and

ISSN:0148-0227    

DOI:10.1029/JA075i001p00050

年代:1970

数据来源: WILEY

摘要:

Measurements of geomagnetically trapped 55‐Mev protons made before and after the detonation of the Starfish nuclear device revealed that at low altitudes the flux increased considerably after the Starfish burst. Theoretical analyses presented in this paper indicate that the flux change resulted from a redistribution of the existing trapped protons in the inner zone. Two processes were found to be capable of altering the proton distribution appropriately: (1) interaction of the protons with hydromagnetic waves produced by the burst and (2) multiple reflections of the protons from a magnetic field inhomogeneity that propagates along magnetic field lines with the local hydromagnetic velocity. If the hydromagnetic velocity is determined from approximate ambient plasma densities, the latter mechanism gives an altitude dependence of the increased flux that is qualitatively in agreement with the measurements. However, much higher plasma densities, or repeated traversals of the field line by the magnetic inhomogeneity, are required to explain the magnitude of the observed flux chang

ISSN:0148-0227    

DOI:10.1029/JA075i001p00057

年代:1970

数据来源: WILEY

摘要:

Amplitude measurements of whistlers and signals from VLF transmitters have been made with the low altitude, polar‐orbiting OGO 4 satellite. Two aspects of these measurements related to the behavior of the waves near the magnetic equator are described and interpreted: (1) Daytime spectrograms taken near the magnetic equator show a remarkable high‐frequency cutoff in the amplitude of the VLF whistler waves. The cutoff frequency decreases as the satellite approaches the magnetic equator, and sometimes all signals drop below the equipment threshold. This feature is also present when the signals from different VLF transmitters are simultaneously observed. It is shown that the above phenomenon is explained primarily by absorption in theDandEregions of the ionosphere and by the daytime ray trajectories near the equator. (2) During the night, absorption becomes relatively small, but nevertheless an abrupt amplitude cutoff of signals from VLF transmitters may still occur. This nighttime cutoff is explained primarily by defocusing near the equator, which is enhanced for nighttime ionization profiles. The defocusing of the VLF waves depends strongly upon the rapid change of ionization‐gradient occurring between 500 and 1000 km of height and also upon the curvature of the earth’s magnetic field around the magnetic

ISSN:0148-0227    

DOI:10.1029/JA075i001p00069

年代:1970

数据来源: WILEY

摘要:

This paper treats whistler amplification in the magnetosphere for conditions in which an energetic group of electrons interacts with the background plasma to produce wave growth. For the energetic group, the following forms of velocity distributions have been examined: pancake, anisotropic resonance, anisotropic Maxwellian, and an isotropic Maxwellian with loss‐cone. The work is distinguished from nearly all previous studies in that each case is subjected to rigorous stability analysis to determine whether the predicted instability should cause wave growth in time, or in space. This is very important in determining whether whistlers will be amplified when passing through an active region, or whether the region will simply be the site of continuous noise generation. The broad general conclusions of the work confirm that the presence of any anisotropy such that the particle energy transverse to the magnetic field is greater than that parallel to the magnetic field always causes instability in some sense. For the cases examined, the instability is generally amplified spatially until this ratio reaches some critical value, and temporally for further increases. The results are discussed in relation to observed whistler amplification and VLF emission

ISSN:0148-0227    

DOI:10.1029/JA075i001p00085

年代:1970

数据来源: WILEY

摘要:

Certain VLF noise phenomena commonly observed with electric dipole antennas on the Alouette, OGO, and Injun 5 spacecraft have been associated with the lower hybrid resonance frequency of the ionospheric medium in the vicinity of the spacecraft. By using simultaneous VLF and ion mass spectrometer data from OGO 4, it has now become possible to compare the characteristic frequencies of these noise bands with the lower hybrid resonance frequencyfLHcalculated directly from ion composition measurements. The results of the study show a clear correspondence between the independent observations over a wide range of variation offLH. Some differences between the VLF and the spectrometer results are also evident and suggest that the characteristic frequencies of lower hybrid resonance noise phenomena observed by satellite‐borne VLF receivers may not always be determined in the immediate vicinity of the spacecraf

ISSN:0148-0227    

DOI:10.1029/JA075i001p00097

年代:1970

数据来源: WILEY

摘要:

A model current system, in which magnetospheric and ionospheric sections are connected by currents flowing along the geomagnetic field lines, is proposed to represent the current system responsible for polar magnetic substorms. The magnetic perturbations from model current systems of this type are studied in terms of elementary loops, whose magnetic effects are evaluated numerically. The influence of currents induced in the ground is studied for a time‐independent case, but it is found that such effects do not change the gross character of the perturbation pattern. Using a north‐south chain of stations and an appropriate coordinate system, the model predictions are compared with the magnetic variations observed during some substorms. It is found that the model is capable of explaining the gross features of the magnetic perturbation pattern observed. However, at times there are minor deviations from the predictions, which suggest the presence of additional ionospheric and magnetospheric current syst

ISSN:0148-0227    

DOI:10.1029/JA075i001p00107

年代:1970

数据来源: WILEY