Simultaneous ground-satellite observations of structured Pc 1 pulsations

Structured Pc 1 pulsations are investigated using simultaneous multipoint ground-satellite observations recorded on September 10, 1986, during Viking orbit 1103. The multipoint Pc 1 observations were acquired using the Viking magnetic field experiment at 13,550 km altitude from L = 5.1 to 5.5 and three Finnish ground stations at Rovaniemi, Ivalo, and Kilpisjarvi. These stations are all located within 30 min magnetic local time and 1 degrees in latitude of the ionospheric field line footprint of the Pc 1 source field line. Structured Pc 1 pulsations between 0.5 and 1.0 Hz were observed both on the ground and in space at similar frequencies, with similar frequency dispersion, and with a similar repetition period. The wave source region, based on Viking Langmuir probe observations, was just inside the plasmapause. The wave transit time between Viking and the ground was 12 +/- 2 s, where Viking leads the ground. This implies that the waves propagate downward from Viking to the ground, consistent with previous downward Poynting flux estimates.