We have constructed a mathematical model of the magnetosphere in which a large‐scale uniform electric field, representing plasma flow from the tail, is superimposed on the geomagnetic field. In addition, the model includes a corotation electric field and an electric field resulting from the conductivity of the plasmasphere. Drift paths of charged particles with various energies are traced out in the equatorial plane, assuming that these particles may enter the magnetosphere through the tail. It is found that an electric field of 0.3 mv/m (across the tail) forms a forbidden zone for thermal particles that is approximately the size and shape of the plasmasphere. The electric field model is also found to provide a qualitative explanation for such varied phenomena as asymmetric ring currents, field‐aligned currents in the magnetosphere, and the existence of an abrupt inner termination to the plasma sheet. The presence of return flow of plasma near the magnetopause resulting from a viscous interaction with magnetosheath plasma is discussed, and it is argued that the return flow does not affect the electric field picture except very near the boundary.
This paper reviews findings since 1966 about the properties of the interplanetary magnetic field; the solar wind plasma; solar wind interactions with the earth, the moon, Mars, and Venus; and the properties and propagation characteristics of energetic solar flare particles. For most purposes the solar wind can be characterized as a fluid that retains some of the properties of its source as it flows outward and that contains an anisotropic temperature distribution and embedded magnetic field. The magnetic field has a sector structure which slowly varies in a manner that resembles the evolution of magnetic features on the solar surface. As the solar wind encounters planetary bodies in its path, the nature of its interaction depends on the size and magnetic properties of the bodies. The solar wind creates a bow shock similar to that at earth as it interacts with Venus, and probably also with Mars. At Venus the plasma is apparently not diverted by a magnetic field, but by the planetary, ionosphere. At Mars the plasma is diverted either by a weak magnetic field or by an ionosphere. Further studies near earth have led to an explanation of the earth's bow shock in terms of hydromagnetic and ion waves. Energetic electrons (>400 kev) have been found in the neutral sheet of the geomagnetotail. The absence of thermal plasma in the earth's outer magnetosphere, beyond the plasmapause, has been explained in terms of a large‐scale convection field. The solar wind interaction with the moon is of an entirely different character. No bow shock is found, and the interplanetary magnetic field appears to convect through the moon. A single‐particle model of the interaction appears adequate to explain the observed phenomena, including the region behind the moon that is void of plasma but contains an enhanced magnetic field. Energetic electrons (20 kev to several Mev), protons (500 kev to 200 Mev), and α particles produced in solar flares have been studied in conjunction with solar X rays and radio bursts. It is now believed that these particles are not necessarily produced in an impulsive event during the flash phase of the flare; proton precursors have been found in some events, and it appears that energetic particles continue to leave the vicinity of the flare for hours or even days. These particles propagate preferentially along interplanetary magnetic field lines. Thus, their velocity distribution is generally anisotropic as long as the injection continues.
Empirical values for radial diffusion coefficients have been calculated for electrons in the range 50–100 kev from L = 4 to L = 7 on the basis of equilibrium fluxes determined from Explorer 12 data. It has been assumed that the principal loss mechanism for these electrons is pitch‐angle scattering by whistlers. The diffusion coefficients derived from the data are several orders of magnitude larger than that expected from Kellogg‐Parker diffusion. Typical values for D1 are 2 RE/day at L = 4.5, 85 RE/day at L = 5.5, and −25 RE/day at L = 6.5. Typical values for D2 are 3 RE²/day at L = 4.5, 63 RE²/day at L = 5.5, and 11 RE²/day at L = 6.5. Also, a sharp peak in the value of D2 occurs at L = 5.75, and D1 changes sign at this point. It is suggested that large‐scale magnetospheric electric fields, of order 1 or 2 mv/m and possibly arising from field‐line merging in the geomagnetic tail, may be responsible for much of this diffusion.
The McIlwain (B, L) coordinate system for describing physical points within the magnetosphere is modified to take account of magnetospheric distortions arising from symmetric ring currents, their associated induction fields, and a constant magnetopause boundary field on the day side of the earth. The goal in making such a modification is to develop a general procedure whereby stormtime magnetospheric distortions may be separated out of satellite particle data, making it possible to observe some of the more subtle aspects of particle behavior that otherwise may be hidden by larger effects. To demonstrate the usefulness of the modified (B, L) system, some new cases of Explorer 12 particle detector data are presented in which the particle configuration appears to be undergoing radial diffusion when plotted in the standard (B, L) system. However, when the counting rates are replotted in the modified system that accounts for ring currents, the diffusion is no longer evident. These cases are thus at least partially explained as being the effect of gross motion of the field lines themselves, rather than particle motion through the field lines.
The purpose of this Letter is to present data indicating the existence of long‐period large‐amplitude variations in the radial positions of the magnetopause on the sunlit side of the earth. During its 112‐day lifetime, the Explorer 12 satellite reported on some 100 passages through the magnetospheric boundary (magnetopause). Data on these boundary crossings have been presented by Cahill and Amazeen [1963], Freeman et al. [1963], Freeman [1964], Konradi and Kaufmann [1965], and Cahill and Patel [1966]. Several of these reports have drawn attention to the occasional existence of ‘multiple boundary crossings.’ These multiple crossings have been interpreted as evidence for rapid movement of the magnetopause past the spacecraft [Freeman, 1964; Konradi and Kaufmann, 1965; and Cahill and Patel, 1966]. Cahill and Patel [1966] have suggested that the boundary motion could, on occasion, be periodic. We hereby examine further the evidence for such a periodicity and report the period derived from one set of two complete cycles to be of the order of ½ hour.
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