Plasma injection and transport in the mid‐altitude polar cusp

DE‐1 hot plasma observations in the mid‐altitude polar cusp have shown evidence of a significant velocity filtering phenomenon which is consistent with a latitudinally narrow region of plasma injection located at a geocentric distance of about 8 R E (in a dipole approximation). Plasma convection from the injection region into the polar cap results in a ‘V’‐shaped log E vs. α o relation at geocentric distances near 4 R E . This velocity filtering effect allows the measurement of much smaller flow velocities (∼10 km/s) than have heretofore been possible with hot plasma measurements. The flows thus determined are consistent with ionospheric flows measured nearly simultaneously by the DE‐2 spacecraft, although the magnitudes of the higher altitude flows are higher by a factor of 2 or more than an ∼r 3/2 dipole‐field mapping would predict.