Comparisons of Polar satellite observations of solitary wave velocities in the plasma sheet boundary and the high altitude cusp to those in the auroral zone

Characteristics of solitary waves observed by Polar in the high altitude cusp, polar cap and plasma sheet boundary are reported and compared to observations in the auroral zone. The study presented herein shows that, at high altitudes, the solitary waves are positive potential structures (electron holes), with scale sizes of the order of 10's of Debye lengths, which usually propagate with velocities of a few thousand km/s. At the plasma sheet boundary, the direction of propagation can be either upward or downward; whereas at the leading edge of high altitude cusp energetic particle injections, it is downward. For these high altitude events, explanations based on ion modes and on electron modes are both examined, and the electron mode interpretation is shown to be more consistent with observations.