A model of the magnetospheric substorm
IT is generally recognised that the Earth's magnetic tail and the plasma sheet play a vital role in the processes responsible for the observational phenomenon known as the magnetospheric substorm. Many different models1–5 of substorm behaviour have been described with differing degrees of success, and to propose another requires some justification. A new model, if it is to be useful, must do two things. It must be specific enough to make quantitative theoretical analysis possible, and it must fit the morphological features more completely or in a more elegant way than other models. In addition, it should be distinctive enough from other models to be separated from them by observational tests. I believe the model presented here has those properties.
Incoherent scatter radar observations during August 4–7, 1972
E- and lower F-region data obtained by the incoherent scatter radar of Chatanika, Alaska were used to analyze the height-integrated Hall and Pedersen conductivities, electric fields, ionospheric currents, electron densities, and rate of heating of the neutral atmosphere by particle precipitation and by electric current dissipation during the period of intense solar flares, August 4-7, 1972. Although the magnetosphere was unusually disturbed magnetically, the radar data were in general not particularly larger than those seen during more quiet periods. Chatanika seemed to be in the auroral oval during nearly the whole of the time period studied, implying a greatly expanded size of the oval.
Magnetic field variations in the near geomagnetic tail associated with weak substorm activity
Magnetic field observations obtained with the UCLA Ogo 5 fluxgate magnetometer on an inbound pass, during which the satellite remained close to the magnetic meridian and traveled almost parallel to and approximately 2 Rr above the expected position of the neutral sheet, are used to illustrate the variations in the configuration of the tail field during weak substorm activity. Beyond 10 Rr from the earth, changes to dipolar fields are accompanied by a reduction in field strength presumably due to plasma sheet expansion. Within approximately 10 Rr changes to a more dipolar field are accompanied by no change or by an increase in field strength. In both regions, these changes are accompanied by turbulence or noise. Occasional twisting of the field out of the usual magnetic meridian is also observed. Magnetic field measurements taken with the synchronous equatorial satellite ATS 1 show that the magnetic signature of the expansion phase of a substorm as observed at 6.6 Rr on the night side of the earth is an increase in the magnitude of the field from a depressed state accompanied by a return to a more dipolelike field [Cummings et al., 1968; Lezniak and Winckler, 1970]. Changes in the configuration of the magnetic field in the geomagnetic tail in the region from 25 to 33 Rr behind the earth at times of auroral zone activity were recently described by Fairfield and Ness [1970]. They find that close to the expected position of the neutral sheet these changes consist of a gradual increase of field magnitude, probably associated with a thinning of the plasma sheet, followed by a rapid decrease of the field magnitude, presumably as the plasma sheet expands. Simultan