MULTIPOINT RECONNECTION IN THE NEAR-EARTH MAGNETOTAIL - CDAW-6 OBSERVATIONS OF ENERGETIC PARTICLES AND MAGNETIC-FIELD

The Coordinated Data Analysis Workshop (CDAW 6) substorm event at 1054 UT on March 22, 1979, is studied using energetic particle (> 20 keV) data from the medium-energy particle experiment of ISEE 1 as well as high-resolution magnetometer data of ISEE 1 and 2. These analyses cast new light on the structure and temporal evolution of the plasma sheet near 15 R(E) during the substorm. These changes are generally consistent with predictions from the near-Earth reconnection model of substorms, modified to include subsidiary plasma and field structure on scales of a few Earth radii. In particular, the onset of streaming flow, nearly aligned with magnetic field lines, of energetic ions and electrons in all available energy channels and its reversal and subsidence are closely correlated with substorm phases. The energetic particles (which are isotropic during the growth phase) begin streaming tailward right after the expansion onset. They reverse their sense of flow in the midexpansion phase. The magnetic field variations suggest that two small magnetic island structures embedded within the plasma sheet moved tailward past the spacecraft shortly after the substorm expansion onset. These structures may be signatures of small-scale multisite reconnection associated with the formation of the near-Earth neutral line. Some magnetic and particle signatures not anticipated in the description of the substorm based on a two-dimensional model of the neutral line are discussed and shown to be reasonable for plausible extensions of the model.