CUTLASS observations of convection in the cusp region

The Finnish radar of CUTLASS has been operational since February 1995. Between 0620 and 0800 UT on August 25 1995, a region of ionospheric scatter, which was limited to only a few degrees of magnetic latitude, moved poleward at a rate of some 7 degrees per hour. The line of sight velocity measurements on a special high time resolution beam indicate a flow reversal boundary which moved poleward throughout the interval. Flow was towards (away from) the radar on the poleward (equatorward) side of the boundary. The flow towards the radar along this beam was at a high speed, >800 m s−1, while the speed away from the radar was less than 200 m s−1. Spatial plots indicate high speed flow away from the radar in the west of the field of view. A tentative interpretation is that the high speed flow is caused by lobe cell reconnection while the low speed flow is associated with either the contraction of the polar cap or due to viscous processes at the magnetopause.

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