摘要:

In the summer of 1971 we conducted new measurements of the primary electron spectrum from 1 to 20 Gev with our electron spectrometer telescope at Fort Churchill. This telescope has been calibrated by using electrons and pions of 0.5–15 Gev at Slac (Stanford Linear Accelerator) in early 1971 and again in 1972. The differential primary electron spectrum over the energy range 3–20 Gev is given bydj/dE= 100/E3±0.2el/m² ster sec Gev, the integral spectrum byJ(E)= 50/E2±0.2. These intensities are considerably lower than many earlier measurements above ∼5 Gev. It is observed that many showers have anomalous lateral distributions as determined in our telescope and must be rejected. This directly leads to the lower intensities. Our calibration results suggest that these events are due to interactions of high‐energy protons. Our measured primary electron spectrum is uncomfortably close to that calculated for secondary electrons produced by the interaction of cosmic ray nuclei with interstellar hydrogen in the galaxy, and therefore the question of the origin of the high‐energy electrons is reopened. The problem of the age of cosmic ray electrons must also be reexamined if our measured spectrum is found to extend to still hig

ISSN:0148-0227    

DOI:10.1029/JA078i001p00001

年代:1973

数据来源: WILEY

摘要:

Flux anisotropies in interplanetary space were investigated for protons with E>0.66 Mev and electrons with E>400 kev. Data were taken from the University of Chicago charged‐particle telescope aboard the deep‐space probe Pioneer 7 and from the Goddard Space Flight Center magnetometer aboard the same spacecraft. Flux anisotropies lying to the east of the average interplanetary magnetic field direction were first reported by McCracken et al. (1971), late in a solar particle event, for proton energies>7.5 Mev. This work extends this investigation to much lower proton energies, studies the proton and electron anisotropies during both early and late phases of a particle event, and makes use of detailed magnetic field data. The investigation consists of two parts, a study of many periods taken at random during solar events, for both protons and electrons, and a detailed analysis of one period, early in an event, during which the magnetic field was near the solar direction. In the first part the study shows that the proton and electron anisotropies are almost always directed from east of the magnetic field direction. In the case of the 400‐kev electrons, the very small Compton‐Getting anisotropy allows a direct measurement of the flux, indicating an electron flux transverse to the average field direction. For the protons, since no selection was made favoring late or early phases of the particle events, the fact that an eastward anisotropy is always measured leads to the conclusion that a low‐energy proton flux component is present transverse to the field. For the case studied in detail, detailed time resolution was obtained of the proton anisotropy at energies>0.66 Mev. This was compared with fine‐scale magnetic field measurements, establishing the presence of a constant offset between field and anisotropy direction, even at times when the magnetic field was in the solar direction. This observation establishes directly the existence of a significant low‐energy proton flux component transverse to the average interplanetary fi

ISSN:0148-0227    

DOI:10.1029/JA078i001p00012

年代:1973

数据来源: WILEY

摘要:

During the initial anisotropic phase of solar particle events, the flux in the radial direction is considerably less than that from the garden hose field direction. An analysis based on the theory of charged particle transport in random magnetic fields has been conducted to determine the pitch angle distribution of particles with respect to the garden hose field lines. With the commonly observed magnetic field power spectral density functions, the model reveals that the flux is proportional to cos δ, where δ represents the angular separation from the garden hose direction. This theoretical result is verified by the analysis of relativistic solar particle observations during the appropriate anisotropic phases of several otherwise dissimilar ground level events; i.e., those of May 4, 1960; November 12, 1960; November 18, 1968; and February 25, 196

ISSN:0148-0227    

DOI:10.1029/JA078i001p00029

年代:1973

数据来源: WILEY

摘要:

Observations of 1.2‐ to 2.2‐ and 2.2‐ to 8.2‐Mev solar protons at low altitudes are studied with emphasis on the interaction zone between the stable trapping regions and the high‐latitude polar cap region. The data show: the appearance of anisotropic loss cone distribution, indicative of particle trapping, near the cutoff latitude on the dayside hemisphere only; the motion of the anisotropic region to lower invariant latitudes as the geomagnetic storm develops and the subsequent development of an isotropic loss cone distribution; and the movement of the solar proton distribution to stable trapping regions well within the ≥ 280‐kev electron trapping boundary. An explanation for these phenomena is offered in terms of cross‐Ldiffusion in the nightside hemisphere along with the development of some strong pitch angle diffusion process at all longitudes, which drives the ∼1‐Mev solar protons to isotropy in the loss cone. The development of strong pitch angle diffusion is strongly linked to the development of the symmetric ring current. This explanation may account for the relative inefficiency of direct solar proton injection as a source of trapped protons in spite of the fact that the solar protons have access to the stable trapping regions. Although the ∼1‐Mev proton lifetimes will be governed by the pitch angle diffusion process, it is important to note that the minimum pitch angle diffusion lifetime is of the order of or larger than ∼1‐Mev proton drift periods in the regionL≥ 4RE. These effects may also explain the longitudinal uniformity of PCA on the dayside hemisphere as well as some

ISSN:0148-0227    

DOI:10.1029/JA078i001p00037

年代:1973

数据来源: WILEY

摘要:

Measurements of the interplanetary magnetic field taken with Imp 3, Pioneer 6, and Explorer 34 constitute a large portion of the data available at low and moderate solar activity and provide nearly continuous coverage from mid‐1965 through 1966 without radial effects. Study of these observations provides further evidence for the followingBθeffect initially discovered with Mariners 2, 4, and 5. At low or moderate solar activity, the mean value ofBθis negative (approximately northward in our observations) above the solar equatorial plane and positive below it for an interplanetary field directed outward from the sun, and vice versa, for an inward field. Thus, for an outward field, theγ−θcomponent of a line of magnetic force above or below the equatorial plane was skewed relative to in the direction away from the equatorial plane. Comparisons between different spacecraft are di

ISSN:0148-0227    

DOI:10.1029/JA078i001p00051

年代:1973

数据来源: WILEY

摘要:

Solar wind plasma and magnetic field data were used to identify rotational and tangential discontinuities during the first 40 days of the flight of Mariner 5. Of the 40 rotational discontinuities found, 36 were clustered in three distinct 3‐ to 6‐day intervals. These three intervals were characterized by high solar wind bulk velocities, high magnetic field magnitudes, low densities, high correlation between velocity and magnetic field changes, and the presence of smooth Alfvén waves. The rotational discontinuities had magnetic field changes that were generally close to the direction of magnetic field changes for smooth Alfvén waves. Although the primary component of these changes was perpendicular to the equatorial plane for both, the radial component for the discontinuities was generally larger. The normals to the tangential discontinuity surfaces strongly preferred a direction near the ecliptic plane and perpendicular to the spiral field direction. For quiet plasma streams there is evidence suggesting that the least likely directions of changes inBandVnear the discontinuity tended to be distributed along the normal to the discontinuity surface. In disturbed plasma streams the magnetic field also behaved as it did in the quiet stream case, whereas the velocity confinement was only true at the discontinuity and did not persist away from the discontinuity. The least likely directions of change for the magnetic field and velocity near the discontinuities were different from those found overall for the 40 days studied. An examination of the qualitative features of fast and slow plasma streams revealed differences in the behavior of the magnetic field and velocity and their fluctuations, the field magnitude, and the density. It is suggested that these differences are correlated with the occurrence of rotational discontinu

ISSN:0148-0227    

DOI:10.1029/JA078i001p00059

年代:1973

数据来源: WILEY

摘要:

The intensity and spatial variations of the He II 304–A radiation in the night sky were measured to an altitude of 264 km from a sounding rocket launched from Thumba, India, on March 10, 1970. The data obtained are presented in the form of an all‐sky map and are compared with theoretical predictions. The data are not consistent either with diffusive equilibrium models of exospheric helium or with plausible models of helium in the interplanetary medium. The data can be fit with a constant density plasmasphere model bounded at the magnetic shellL= 4 in combination with a tenuous gas of helium ions in the plasma sheet. Numerical results obtained with this model are compared with in situ satellite observati

ISSN:0148-0227    

DOI:10.1029/JA078i001p00071

年代:1973

数据来源: WILEY

摘要:

Lyman α intensity measurements (1216 A) were obtained by a photometer on board the Ogo 5 spacecraft outside the geocorona. The Lyman α emission originating from hydrogen atoms in the upper part of the geocorona was derived from the total measured intensity after subtraction of the extraterrestrial emission. The hydrogen density distribution between 5 and 16REwas deduced. This distribution is consistent with the evaporative atmospheric model of J. W. Chamberlain on the night side. A depletion of atoms found above a distance of 6REon the day side could be accounted for by the action on satellite particles of charge exchange with solar wind protons and by the solar Lyman α radiation pressure, according to numerical computations of both effects. It was also calculated that orbits with a perigee of 2REare rapidly distorted by radiation pressure. The mean time spent in the exosphere by satellite particles on such orbits is only 5 × 105sec, one‐half the ionization lif

ISSN:0148-0227    

DOI:10.1029/JA078i001p00080

年代:1973

数据来源: WILEY

摘要:

The semiannual variation in geomagnetic activity is well established in geomagnetic data Its explanation has remained elusive, however. We propose, simply, that it is caused by a semiannual variation in the effective southward component of the interplanetary field. The southward field arises because the interplanetary field is ordered in the solar equatorial coordinate system, whereas the interaction with the magnetosphere is controlled by a magnetospheric system. Several simple models utilizing this effective modulation of the southward, component of the interplanetary field are examined. One of these closely predicts the observed phase and amplitude of the semiannual variation. This model assumes that northward interplanetary fields are noninteracting and that the interaction with southward fields is ordered in solar magnetospheric coordinates. The prediction of the diurnal variation of the strength of the interaction at the magnetopause by this model, does not, however, match the diurnal variation of geomagnetic activity as derived from ground‐based data. However, predictions of the dependence of geomagnetic activity on the polarity of the interplanetary magnetic field and of a 22‐year cycle in geomagnetic activity are confirmed by studies of ground‐based data. It appears that the mechanism controlling the semiannual variation of geomagnetic activity has been identified but that a quantitative model must await further refinements in our knowledge of the solar wind‐magnetosphere c

ISSN:0148-0227    

DOI:10.1029/JA078i001p00092

年代:1973

数据来源: WILEY

摘要:

We report a study of the substorm‐related variations of the magnetotail plasma sheet. The study uses data, much of it previously published, obtained by Vela and Imp satellites in the range −6RE>XSM>−60RE, whereXSMis geocentric distance measured along the solar magnetosphericxaxis. Evidence is presented that the thickening or recovery of the plasma sheet, which has been shown in Vela satellite measurements (atγ≈ 18RE) to occur late in substorms, is causally related to a rapid poleward shift or ‘leap’ of the principal current of the auroral electrojet evidenced by recovery of magnetic bays at auroral latitudes (65° ≲ λm≲ 70°) and their onset at low polar cap latitudes (e.g., λm≈ 74°). That is, it appears to be inaccurate to regard the thickening of the plasma sheet in the far magnetotail as a process that commences near the earth at the onset of the expansive phase of a substorm and moves more or less uniformly out into the tail as the expansive phase of the substorm evolves. A schematic description of the responses of the plasma sheet to a substorm, based on this study and previou

ISSN:0148-0227    

DOI:10.1029/JA078i001p00109

年代:1973

数据来源: WILEY