We explore the relationship between mid‐latitude and synchronous orbit magnetic signatures and the location of the auroral surge at the onset of three isolated magnetospheric substorms. Mid‐latitude data come from the Air Force Geophysics Laboratory Magnetometer Network, synchronous orbit data from the satellites GOES 2 and 3, and auroral data from Defense Meteorological Satellite Program auroral images and auroral magnetograms. We find that the surge forms with its western edge ∼1 hour west of the longitude where the major axis of the mid‐latitude Pi 2 polarization ellipse is along magnetic north and where the D component perturbation of the magnetic bay is near zero. These observations are in qualitative agreement with a current wedge consisting of a localized upward current in the west and a longitudinally distributed current in the east. At synchronous orbit the longitude of the surge head appears to separate a region to the west where the magnetic field becomes more taillike from one to the east where the magnetic field becomes more dipolar.

Some features of Pi 2 pulsations and magnetic bays observed on the ground using the mid‐latitude Air Force Geophysics Laboratory (AFGL) Magnetometer Network previously have been shown to agree with ideas concerning the development of a substorm current wedge during isolated substorm onsets. In particular, the H and D component magnetic bay perturbations and the azimuths of the horizontal component of the Pi 2 polarization ellipse observed by the AFGL Network have been used to locate the approximate center and azimuthal extent of the substorm current wedge. In this paper we apply this technique to a well‐defined substorm to locate the substorm current wedge position relative to the GOES 2 and 3 synchronous satellites at L ≃ 6.6 and the nearby SCATHA satellite at L ≃ 8.1 to explain the magnetic features observed by those satellites. We find that the two satellites within the current wedge, at a position just after local midnight, simultaneously observe a dipolarization of the background field configuration beginning at the time of the substorm onset; however, the impulsive, irregular oscillations frequently observed at substorm onset are only observed by one of the satellites. The other satellite within the wedge observes a similar disturbance after a 3‐minute delay which may be attributed to an intensification or movement of currents in the downward current portion of the substorm current wedge. The satellite west of and outside the current wedge observes no significant change in the magnetic field during the event. These observations illustrate the difficulties of interpreting single‐satellite measurements of substorm effects. If magnetic data from only the satellite west of the wedge had been available, the substorm would have gone undetected. Furthermore, an incorrect substorm onset time could have been deduced from one of the satellites within the wedge.

Pi 2 pulsations are often used to indicate the start of the substorm expansion phase. In this report the relationship between the Pi 2 polarization pattern observed at a mid‐latitude longitudinal chain of stations and synchronous orbit magnetic activity is explored. Eighteen single‐ and multiple‐substorm‐onset intervals, consisting of 55 Pi 2's, are examined using data from the Air Force Geophysics Laboratory Magnetometer Network and the synchronous orbit satellites GOES 2 and 3. Magnetic fluctuations at synchronous orbit are found to be enhanced when the satellite is near the Pi 2 pattern center, defined as the longitude where the major axis of the polarization ellipse is along the H axis. The pattern center is also observed to separate regions of dipolarization and more taillike magnetic signatures. East of the pattern center the field inclination becomes larger, i.e., more dipolelike, while west of the center the field inclination becomes smaller, i.e., more taillike. Although regions of substorm activation, as determined by the Pi 2 pattern, move between onsets during multiple‐onset events, no consistent azimuthal motion was found.

On March 9, 1978, a sounding rocket launched from Poker Flat, Alaska, at 2200 LT, made a four-component measurement of a 0.5 Hz hydromagnetic wave as the payload crossed the poleward boundary of a quiet homogeneous auroral arc. An energy flux of •10 -6 W/m z was observed propagating upward with a left-handed polarization within the arc, and a flux 6 times greater was observed propagating downward with a righthanded polarization on the arc boundary. The waves were identified as shear mode Alfv•n waves. Various models for the source of the free energy are discussed with the conclusion that the most likely production mechanism was either the electromagnetic or electrostatic Kelvin-Helmholtz instability.

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