A survey of the equatorial pitch angle distributions of energetic electrons is provided for all local times out to radial distances of 20 RE on the night side of the earth and to the magnetopause on the day side of the earth. In much of the inner magnetosphere and in the outer magnetosphere on the day side of the earth, the normal loss cone distribution prevails. The effects of drift shell splitting (that is, the appearance of pitch angle distributions with minimums at 90°, called butterfly distributions) become apparent in the early afternoon magnetosphere at extended distances, and the distribution is observed in to 5.5 RE in the nighttime magnetosphere. Inside ∼9 RE the pitch angle effects are quite energy dependent. Beyond ∼9 RE in the premidnight magnetosphere during quiet times the butterfly distribution is often observed with j⊥/j∥ < 1/100. It is shown that these electrons cannot survive a drift to dawn without being considerably modified. The role of substorm activity in modifying these distributions is identified.

Paper number 7A0794. 0148-0227/78/027A-0794505.00 663 substorm expansions then make only small contributions to the total convection pattern.Similarly, the ground magnetic disturbances may then be caused mainly by SqP currents and enhanced currents due to strong particle precipitation rather than by substorm-associated current wedges.During this quasi-steady state the tail reconnection rate appears nearly to balance the dayside merging rate, allowing most energy extracted from the solar wind to be released continuously rather than to be first stored in the tail.It seems that a large-scale substorm expansion may be triggered if this convection mode is perturbed, for instance, bY a significant reduction of the imposed convection electric field. Sergeev, 1977; Kokubun et al., 1977]. This activity seems to occur during long intervals of auroral zone bay activity and southward pointing interplanetary magnetic field (IMF). The relation between conditions in the solar wind and magnetospheric activity, in particular, the occurrence and magnitude of substorms, have been studied extensively [e.g., Rostoker and F•lthammar, 1967; Nishida, 1968; Arnoldy, 1971; Kokubun, 1971; Foster et al., 1971; Coroniti and Kennel, 1972; Akasofu et al., 1973; Caan et al., 1973; Akasofu, 1975]. A southward turning of the IMF (i.e., B z < O) proves to be of major importance, since it results in enhanced merging between interplanetary and geomagnetic field lines, enhanced magnetospheric convection, and a buildup of magnetic energy in the tail lobes. During quiet times, energy is thought to be released at a low rate as open field lines are reconnected across the neutral sheet in the distant tail and convected toward the inner magnetosphere. An explosive release of larger amounts of energy occurs during substorm expansion Sakurai, T., and T. Saito, Magnetic pulsations Pi 2 and substorm onset, Planet. Space Sci., 24, 573, 19 76. Sergeev, V. A., On the state of the magnetosphere during prolonged period of southward orientated IMF, Phys. Solarterrestris, in press, 1977. Schindler, K., A theory of the substorm mechanism, J. Geophys. Res., 79, 2803, 1974. Troshichev, 0. A., B. M. Kuznetsov, and M. I. Pudovkin, The current systems of the magnetic substorm growth and explosive phases, Planet. Space Sci., 22, 1403, 1974. Vasyliunas, V. M., Theoretical models of magnetic field line merging, 1, Rev. Geophys. Space Phys., 13, 303, 1975. Electron pitch angle distribution throughout the magnetosphere as observed on Ogo 5, J. Geophys. Res., 78, 164, 1973a.

Particle flux variations associated with low‐frequency hydromagnetic waves have been examined by using Ogo 5 data obtained with the Lockheed ion mass spectrometer, the Lawrence Livermore Laboratory electron and proton spectrometers, the University of California at Los Angeles (UCLA) energetic electron spectrometers, and the UCLA flux gate magnetometer. It was found that quasi‐periodic perturbations in the thermal ion (E ≤ 600 eV), energetic electron (E ≥ 50 keV), and proton (E ≥ 100 keV) fluxes were usually associated with the occurrence of Pc 5 waves in the region of L = 6–11. Amplitudes of perturbations in the ion density, inferred from the assumption that the ambient cold plasma was at rest, often reached 10–50 ions/cm³. The ion density variations were usually found to be either 90° or 270° out of phase with the magnetic perturbations. It is concluded that these large apparent perturbations of ion density are attributable to drift velocity variations of the ambient plasma induced by hydromagnetic waves. From the phase differences between the thermal particle flux and the magnetic field variations it is argued that the time‐averaged Poynting flux of Pc 5 waves along the ambient magnetic field is approximately zero; this indicates that Pc 5 waves are standing waves along the field line. Flux modulations of the energetic electrons and protons are more complicated than those of the thermal ions. The relative phase of the variations is often found to depend on the energy of the particles. We have found that the proton modulations are usually larger in the morning than in the afternoon, while electron modulations dominate in the afternoon. This fact is consistent with an azimuthal phase velocity of the Pc 5 waves directed from noon to midnight in both the morning and the afternoon and indicates that drift motions of energetic particles can interact strongly with the oscillations of field lines; these observations are consistent with the energy source of the Pc 5 oscillations originating mainly from the Kelvin‐Helmholtz instability at the magnetopause as suggested in recent theories.

Bursts of energetic protons, 100–1300 keV, were observed on Ogo 5 in the magnetosheath and upstream wave region beyond the earth's bow shock during periods of generally enhanced solar and magnetic activity in 1968. From these data, we present the first comprehensive study of energetic protons in the magnetosheath. These magnetosheath protons are found to be directional with the peak flux directed downstream. Typical downstream‐to‐upstream flux ratios are from 10/1 to 20/1 in most regions but often as great as 100/1 near the afternoon magnetopause. The fluxes correlate roughly with magnetic activity. The downstream flux can be expressed as j(> 100 keV) = 500 × 100.412Kp/cm² sr s to about an order of magnitude. Peak unidirectional fluxes near the magnetopause are often similar in spectra and intensity to the peak intensities of trapped fluxes in the nearby magnetosphere. Enhanced proton fluxes occur in the sheath in correlation with depressions in the sheath magnetic field and in correlation with enhanced turbulence. Often at such times, magnetopause boundary layer effects are observed. Energetic proton bursts, in agreement with earlier observations (Lin et al., 1974), are also observed in the upstream wave region beyond the shock, predominately on the morning side of the earth. They correlate well with the wave observations; however, on occasion, they are offset as much as 10 min in time. Directional observations indicate downstream‐to‐upstream directed flux ratios of 10/1 as being typical of the upstream wave region. The directional anisotropies in both the sheath and the upstream wave regions are largely explained by combinations of the Compton‐Getting effect, proton flux spatial gradients, and the free streaming of protons along field lines from an upstream source region. Possible sources of the energetic magnetosheath protons are magnetospheric escape or the energization of low‐energy protons in the magnetosheath, shock, and/or upstream wave region. No strong preference is presently ascribed to any one source.

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