Two barium plasma injections into the northern magnetospheric cleft

Barium plasma was injected into the northern magnetospheric cleft twice during January, 1975. Lofted by rockets launched after local magnetic noon from Cape Parry, NWT, Canada, high‐explosive shaped charges compressed hollow barium cones to generate vapor jets moving upward with initial velocities near 13 km/s parallel to the geomagnetic field. Barium plasma streaks created by solar photoionization of the vapor were convected through the polar magnetosphere and were observed optically from airborne and ground‐based sites until about 40 min after injection. Numerous indicators were monitored to determine the degree of magnetospheric disturbance; ionosondes at Cape Parry and Sachs Harbour, NWT, monitored latitudinal cleft motions preceding rocket launch. Spectrometers in the payloads recorded charged‐particle fluxes during both flights. The first injection occurred poleward in the cleft with subsequent plasma convection antisunward across the polar cap; the second occurred centrally with plasma convection duskward at constant magnetic latitude.