Observation and Modeling of Energetic Particles at Synchronous Orbit on July 29, 1977

In the 12 hours following a worldwide storm sudden commencement at 0027 UT on July 29 there was a series of at least four magnetospheric substorms, the last and largest of which exhibited an expansion phase onset at ∼1200 UT. Data from six spacecraft in three general local time groupings (0300, 0700, and 1300 LT) were examined, and vector magnetic field data and energetic electron and ion data from ∼15 keV to >2 MeV were employed. Four primary types of studies were carried out: (1) timing and morphology of energetic particle injections; (2) variation of particle phase space densities f(µ = p²/2mB), using local magnetic field and particle flux data; (3) measurement of boundary motions, using high-energy ion gradient anisotropies; and (4) adiabatic modeling, which included injection, large-scale convection, corotation, and gradient drifts. For the 1200 UT substorm it is concluded that there was a substantial flux dropout in a broad sector near local midnight because of a large-scale boundary motion, followed by a recovery to a predropout configuration. There were then several subsequent injection events with distinct onsets (extending as far eastward as 0300 LT), for which ion anisotropy information suggests an inward motion of particles from outside of geostationary orbit. Particle drift information reveals that these particles drifted azimuthally completely around the earth. It is also concluded from the phase space density studies that ‘fresh’ particles with magnetic moments of up to at least several hundred MeV/gauss were injected near geostationary orbit. The present adiabatic convection model can explain the observed injection of large magnetic moment particles from the plasma sheet into synchronous orbit, although physical elements of the normal model must be altered somewhat.