Multipoint observations of global magnetospheric compressions

The magnetic field experiment on the Viking satellite detected long‐period compressional oscillations with amplitudes ranging from 2 to 5 nT and periods ranging from 7 to 23 min on nine Viking orbits covering a wide range of polar and subauroral latitudes during the period from March to August 1986. We present a case study of an event on June 18, 1996, in which similar long‐period pulsations were also observed by a global network of more than 50 ground magnetometers and by the GOES‐5 and GOES‐6 spacecraft. The magnetic field variations throughout the auroral, midlatitude, and equatorial regions, at Viking, GOES‐5, and GOES‐6 were approximately in phase, whereas the variations at some morningside stations were a half‐wave period out of phase. We interpret these long‐period oscillations as evidence for periodic compressions and inflations of the magnetosphere driven by solar wind pressure pulses. The relative time delays of the peak variations observed by GOES‐5, GOES‐6, Viking, and the ground‐based stations are consistent with an event originating on the prenoon magnetopause whose signatures spread both poleward and antisunward on both sides of local noon.