THE DAYSIDE AURORAL-ZONE AS A HARD TARGET FOR COHERENT HF RADARS

Observations from the CUTLASS Finland coherent HF radar on 23 February 1996 are employed to demonstrate that changes in propagation mode fro m 1/2 F to 1 1/2 F and back again, determined from elevation angle mea surements, do not significantly alter the ranges over which ionospheri c backscatter is observed. This indicates that the latitudinal extent of backscatter in the dayside auroral oval and cusp region correspond to the boundaries of geophysical processes, as opposed to limits in th e illumination of the F region ionosphere by the radar. Hence, the HF radar technique is confirmed as an excellent diagnostic of the cusp an d other dayside regions.