Magnetic local time dependency on cusp ion velocity dispersions in the mid-altitude cusp

Observations of cusp ion velocity dispersions made by the TIMAS instrument on the Polar spacecraft in the mid-altitude cusp during intervals of northw ard interplanetary magnetic field (IMF) reveal a clear ordering with magnet ic local time (MLT). Between 1100 and 1300 MLT the injected ion velocity in creased with invariant latitude for 78% of the cusp crossings, between 0900 and 1100 MLT this percentage reduced to 35% and between 1300 and 1500 MLT the percentage reduced to 57%. In contrast similar observations made during intervals of southward IMF revealed no MLT dependency. Between 0900 and 15 00 MLT the injected ion velocity increased with invariant latitude for only 17% of the observed cusp crossings. We suggest that the difference in the MLT dependency between northward and southward IMF can be best explained by the different characteristics of polar convection patterns for sub-solar a nd lobe reconnection.