July 29, 1977, Magnetospheric studies: Impulsive waves, global dynamics and geomagnetic indices
The day in question included intervals of intense geomagnetic activity, with an initial impulsive response to an interplanetary shock followed by numerous substorms. The latter half of the day was of special interest because the activity was limited to high latitudes in the northern polar cap, where it was substantial. The immediate response of the magnetosphere to changes in the solar wind (shock or other) was considered in studies of impulsive waves, which were traced through the magnetosphere to the ground and interpreted in terms of fast-mode wave propagation. The geometry and microstructure of the magnetopause, following the arrival of an interplanetary shock, were analyzed with data from near-geostationary satellites. The global magnetic geometry was modeled for the entire day. Plasma sheet convection was monitored at low and high altitudes. A model of particle convection during the first quarter of the day gave important evidence that the convection electric field penetrated to small radial distances for extended intervals. A large substorm at midday was unusually well documented with data from geostationary spacecraft and ground observatories. In reviewing those data this paper addresses the question of control of the local time of substorm onset. A model is presented that relates the local time of substorm onset to the sector of the tail earliest stressed following the onset of dayside reconnection. The late-day data provided evidence of lobe magnetic field reconnection when the solar wind magnetic field was pointing north. This paper marshals the evidence for different reconnection patterns and introduces an alternative pattern not previously considered.
- Research Organization:
- Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California Los Angeles, California 90024
- OSTI ID:
- 6706576
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 87:A8
- Country of Publication:
- United States
- Language:
- English
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