摘要:

Evidence is presented for the existence of statistically significant broad‐band fluctuations, far above noise level, in the cosmic‐ray flux observed inside the magnetosphere. The observed intensities at the polar cap at both low and high energies were analyzed, and power spectra of the cosmic‐ray scintillations are presented and discussed. The low‐energy data obtained during quiet times strongly suggest that, if δjis the fluctuation in intensity about the meanj0, the spectrum of δj/j0is nearly constant for widely varying values ofj0. The spectra are roughly inverse power laws in frequency, with slopes of −1.5 to −2. The magnitudes of the spectra of δj/j0are much smaller at high energies than at low. A plausible, illustrative model for the propagation of cosmic rays through the turbulent magnetic field in the magnetosheath is presented, and a relationship between the observed cosmic‐ray power spectrum and the magnetosheath magnetic‐field power spectrum is obtained. It is shown that magnetic fluctuations in the magnetosheath can reasonably account for the observed cosmic‐ray scintillations in the low‐energy region (1 to 40 Mev), although other interpretations cannot be ruled out. Other possible mechanisms are briefly discussed. The scintillations of cosmic rays of neutron monitor energies are not explained by this model and may be in

ISSN:0148-0227    

DOI:10.1029/JA077i034p06639

年代:1972

数据来源: WILEY

摘要:

Quasi‐periodic 12.5‐min fluctuations occurred in the counting rates of Geiger counters and a neutron counter during level flight of a balloon over Wilkes, Antarctica, on September 3, 1966. Correlated fluctuations were observed in the Wilkes magnetometer record. A large solar cosmic‐ray event was in progress at the time of the flight. The periodic modulation process is shown to have an energy dependence with a peak at about 50 Mev for solar protons. No periodicity was detected in the Geiger counter telescope rate, which had a proton threshold energy of>110 Mev. It is suggested that the modulation is a result of scattering by hydromagnetic waves in the distant part of the tail. The protons withE>110 Mev did not pass through the modulating region and probably gained access to the magnetosphere on the da

ISSN:0148-0227    

DOI:10.1029/JA077i034p06656

年代:1972

数据来源: WILEY

摘要:

Observations of scattered solar hydrogen Lyman‐α radiation made with detectors carried by satellites Vela 4A and 4B show a repetitive and marked asymmetry in the Lyman‐α flux. The detectors look radially outward from the earth at an altitude of 110,000 km. The axis of the 34° angle of view lies in the plane of the circular satellite orbit, which is inclined 32° to the equator. The distinctive characteristic of the data for the period May, 13, 1967, to July 31, 1967, is a broad maximum in the flux. In a preliminary interpretation, we assumed the detectors were above the hydrogen geocorona and that the scattering hydrogen, which gives rise to the broad maximum, must be in interplanetary space. Detailed analysis of data for many orbits indicates that the most precisely located feature of the data, the leading edge of the broad maximum, moves in right ascension at about the same rate and in the same direction as the motion of the earth projected on the celestial sphere. Thus, a significant part of the scattering hydrogen moves with the earth, and the observations are interpreted as evidence for an aspherical geocorona with an increased density of hydrogen beyond 18REon the night side. The view direction is above the ecliptic plane when the maximum is observed. After an estimated interplanetary component is subtracted from the observed maximum flux, the scattered Lyman‐α intensity from telluric hydrogen beyond 18REis about 150 rayleighs. The column density of hydrogen above 18REwhen the maximum is observed is 6 to 7 × 1010atom cm−2in the plane of the sa

ISSN:0148-0227    

DOI:10.1029/JA077i034p06665

年代:1972

数据来源: WILEY

摘要:

The charged particle lunar environment experiment (CPLEE), a part of the Apollo 14 lunar surface package, is an ion‐electron spectrometer capable of measuring ions and electrons with energies between 40 ev and 50 kev. The instrument, with apertures 26 cm above the surface, has detected a photoelectron gas layer above the sunlit lunar surface. No detectable flux above 200 ev has been observed. Experimental data for periods while the moon was in the earth's magnetotail for electrons with energies 40 ev ≤E≤ 200 ev follow a power‐law spectrumj(E) =j0(E/E>0)−μwith 3.5 ≤ μ ≤ 4. In the absence of photoelectrons withE>200, we assume that the surface potential is at least 200 volts. The modulation of this potential in the presence of intense plasma‐sheet fluxes has been observed. Also, a detailed history of the February 10, 1971, total lunar eclipse, to determine the source distribution of high‐energy solar photons, is presented. A classical penumbral‐umbral behavior indicates that at the time of the eclipse the emission of higher‐energy photons was uniform over the solar disc. Numerical solutions for the variation of electron density and potential as functions of height above the lunar surface were obtained. The solar photon spectrumI(hν), obtained from various experimental sources, and the photoelectron yield function of the surface materials,Y(hν), are two parameters of the solution. Energy spectra at the height of the measurements for various values ofY(hν) were computed until a fit to experimental data was obtained. Using a functional formY(hν) = [Y0(hν−W) / (W/ 2)] for 6 ev ≲hν≲, 9 ev andY(hν) =Y0forhν>9 ev, where the lunar‐surface work functionWwas set at 6 ev, we calculated a value ofY0= 0.1 electrons/photon. The solution also showed that the photoelectron density falls by 5 orders of magnitude within 10 meters of the surface, but the layer actually terminates several hundred meters above this height. A hydrostatic model of the photoelectron layer has also been developed. It is shown that the numerically calculated pressure, density, and potential can be approximated by solving the hydrostatic equations with an equation of stateP/n1/2= constant out to 200 cm from the surface. Beyond this height, the equation of state shifts t

ISSN:0148-0227    

DOI:10.1029/JA077i034p06671

年代:1972

数据来源: WILEY

摘要:

It is inferred from measurements of proton fluxes with electrostatic analyzers on the Vela satellites that plasma leakage from the magnetosphere into the magnetosheath is rather commonplace and may be strongly enhanced during magnetospheric substorms. It is suggested that this leakage accounts for the loss of at least some of the plasma that leaves the thinning plasma sheet early in a substorm. When a Vela satellite is in the magnetosheath, its electrostatic analyzer detects a flux of protons of energy of ∼1 kev that is strongly modulated, owing to the rotation of the satellite in the rapidly flowing magnetosheath plasma. When they are in this environment, the analyzers sometimes also detect fluxes of protons of energy of ∼10–30 kev with intensities characteristic of those in the magnetotail plasma sheet, and in many cases these fluxes appear during substorms. Simultaneous measurements by two Vela satellites, one in the magnetosheath and one in the solar wind, show conclusively that these protons do not originate in the solar wind. Spatial variations of their intensity across the magnetosheath suggest further that they come not from the bow shock but from the magnetos

ISSN:0148-0227    

DOI:10.1029/JA077i034p06688

年代:1972

数据来源: WILEY

摘要:

Data from the auroral particles experiment on Ogo 4 were used to study effects of interplanetary magnetic‐field latitude and dipole tilt angle on high‐latitude precipitation of low‐energy electrons. It was found that: (1) The low‐latitude boundary of polar‐cusp electron precipitation at 0900 to 1500 MLT moves equatorward by several degrees during substorms and, in the absence of significant substorm activity, after a period of southward interplanetary magnetic field. This behavior is interpreted to result from erosion of dayside magnetic flux into the tail and to be a part of the substorm growth phase. Comparisons of southward solar‐wind magnetic flux and the eroded magnetic flux indicate a merging efficiency of 5 to 30%. Expected cross‐tail electric potentials lie in the range 36 to 84 kv, in reasonable agreement with observation. (2) With times containing substorm activity or a southward interplanetary magnetic field eliminated, the low‐latitude boundary of polar‐cusp electron precipitation is found to move by approximately 4° over the total yearly range of tilt angles. At maximum winter and summer conditions, the invariant latitude of the boundary is shown to shift by approximately −3° and +1°, respectively, from its equinox location. This same asymmetry is found in calculations of the invariant latitude of the first open field line in the Mead‐Fairfield model magnetosphere. The observed polar‐cusp lower boundaries lie approximately 3° below the calculated first open field lines and coincide with the average>35‐kev electron bounda

ISSN:0148-0227    

DOI:10.1029/JA077i034p06696

年代:1972

数据来源: WILEY

摘要:

A pronounced longitude variation in the intensity of locally mirroring protons above 100 kev in theLrange 3.5–5 at low altitudes is observed. The observations can be accounted for by a steady‐state pitch angle diffusion process. The pitch angle diffusion coefficient for protons mirroring near the loss cone atL= 4 is found to be about 10−6

ISSN:0148-0227    

DOI:10.1029/JA077i034p06708

年代:1972

数据来源: WILEY

摘要:

Extensive observations of midlatitude depletions in electron and total ion density by both direct and indirect techniques have prompted numerous studies of the possible association between these troughs, observed both in theFregion and in the topside ionosphere, and the plasmapause. Within this work, one basic problem arises in that, although the plasmapause has been detected as a global phenomenon by both VLF and ion composition measurements, the electron and ion density troughs have been identified primarily as nightside features. This problem, as well as the difficulty in explaining various inconsistencies in relating the position of the plasmapause and the ionization trough, is explained by a close examination of the ion composition, generally unavailable in previous trough studies. In particular, ion composition results from the polar‐orbiting Ogo satellites identify the persistence of a pronounced light‐ion trough (LIT) in H+and He+, often identified by order‐of‐magnitude decreases in the light‐ion concentrations, that occurs within a few degrees of latitude and reaches residual concentration levels of 10²–10³ ions/cm³ near 60° dipole latitude. The LIT, observed both within the thermosphere and at high latitudes in the magnetosphere, has been correlated directly with the VLF whistler identification of the plasmapause. On the nightside near 1000 km a complex relationship is observed between the dominant ions O+and H+. The rapidly changing mean ion mass observed at the plasmapause typically produces a resultant total ion density distribution of complexity sufficient to confuse correlative studies with the plasmapause, even though the LIT is very sharply defined within the ion composition. On the dayside, where O+is typically the predominant ion near 1000 km, LIT structure is often hidden beneath the O+layer, which may exhibit little or no depletion even though H+and He+show trough structure at the plasmapause. This analysis of the midlatitude topside ion composition indicates the need for caution both in studies of the plasmapause per se and in phenomenological studies such as the relationship between the subauroral red arc and the plasmapause, which are most likely dependent on the detailed information available within the

ISSN:0148-0227    

DOI:10.1029/JA077i034p06716

年代:1972

数据来源: WILEY

摘要:

We have adapted the metal foil sampling technique, which has been used to measure helium, neon, and argon fluxes in the solar wind, to the problem of measuring the fluxes of these gases in the auroral primary radiation. Aluminum and platinum foils have been flown into two bright auroras and have been recovered. The foils have been analyzed for helium and neon isotopes with a mass spectrometer; so far we have only detected4He, but with a more sensitive mass spectrometer it should be possible to detect ³He. In the first flight the precipitating flux of4He with particle energies above about 1 kev was approximately 1 × 106cm−2sec−1, and the backscattered flux was smaller by about a factor of 10. In the second flight the aurora was less bright, and the4He fluxes were lower by a factor of about 2. A rough analysis suggests that the mean energy of the incident particles was>3 kev. These fluxes are consistent with measurements of the ion fluxes observed at high altitudes in the auroral zone and in the magnetosphere, if it is assumed that the helium contributes a few per cent of the total

ISSN:0148-0227    

DOI:10.1029/JA077i034p06724

年代:1972

数据来源: WILEY

摘要:

The morphological characteristics of magnetospheric plasma waves (period τ ∼ 18 to 150 sec) detected at conjugate points nearL= 4 during the winter solstice are studied. No magnetospheric waves that satisfy an imposed strict selection criterion are observed after ∼1700 LT. Approximately half the 94 accepted events are left‐hand polarized. No significant change in the polarization characteristics of the waves is observed as a function of local time. Approximately 16% of the events have opposite polarizations in the two hemispheres. The morphological polarization characteristics are discussed in the context of expected body‐ and surface‐wave polarizations. The observed polarizations do not readily support a surface wave arising from the Kelvin‐Helmholtz instability on the magnetopause as a source for all the events. All but two of the left‐hand and right‐hand wave events were symmetrical about the meridian plane, implying a predominant in‐phase oscillation of theHcomponent of the wave at each station and an out‐of‐phase oscill

ISSN:0148-0227    

DOI:10.1029/JA077i034p06731

年代:1972

数据来源: WILEY