HIGH-ALTITUDE BOTTOMSIDE BUBBLES

The ion drift meter on the polar orbiting DMSP F-10 spacecraft observe d bubble-like features near the magnetic equator that have remarkably continuous transitions in ion concentration (N(i)) and drift velocity, where there is a high positive correlation between upward velocity an d decreased N(i). This is in marked contrast to the virtually disconti nuous transitions that are characteristics of most bubbles. We conclud e that these new features were probably observed on the bottomside of the F-layer at DMSP altitudes (750 - 850 km), much higher than normall y accepted values. These observations were made during Feb.-Mar.-Apr. of 1991, when N(i) exceeded 10(6) cm-3 on nearly every equator crossin g.