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.