Coordination Of The Geosynchronous And Auroral Substorms

Abstract

Studies using data from the ATS-5 geosynchronous spacecraft revealed a clear relationship between midnight region injection events near the spacecraft and auroral displays near the ATS magnetic conjugate point (Hones et al., 1971a; Mende et al., 1972; Eather et al., 1976; Mende and Shelley, 1976). A comparison of ATS-5 particle and magnetic field data with all-sky photographs taken at the conjugate point, Great Whale River, indicated that an injection at geostationary orbit generally corresponded to the brightening of the onset arc when the spacecraft was in the midnight sector (Akasofu et al., 1974). Results such as this whetted the collective appetite. How closely can the initial onset and injection be related to one another in time, do the onset and injection start on the same field field line, does the westward propagation of dipolarization correspond to the westward surge, can one relate the fine structures of the auroral expansion and the dipolarization? As time passed, increasingly precise answers have been given to these and similar questions, and auroral and geosynchronous substorm phenomenology has become more tightly integrated. In this chapter, we sample some of the evidence that supports this statement. The GEOS 2 spacecraft was stationed with its magnetic conjugate point near Kiruna, Sweden, so that the conjugate aurora could be studied with the extensive network of ground-based observatories in Scandinavia (Knott, 1975; Knott et al., 1979). In the first part of this chapter, we review some of the correlation studies carried out in the GEOS 2 project. In one particular series of four substorms, it was found that the dipolarization occurred at the same time as the aurora brightened and expanded poleward over the ground conjugate region (Section 14.2). In another case, a dispersionless injection at GEOS 2 corresponded to an intensification of the auroral X-ray band in Scandinavia (Section 14.2). Westward surges at the auroral conjugate point were associated with dipolarization at the spacecraft on a statistical basis (Section 14.3). Finally, the close relationship between both the auroral and geostationary substorm phenomena was extended to small spatio-temporal scales.