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HF radar backscatter which has been artificially-induced by a high power RFfacility has been demonstrated to provide ionospheric electric field data ofunprecedented temporal resolution and accuracy. Here such data, induced bythe SPEAR high power radar on Svalbard, are used to investigate ULF waveprocesses observed by the CUTLASS HF radars. Observations are presented ofboth waves with a large-scale nature, driven externally to the magnetosphereand those with small azimuthal scale lengths, driven by wave-particleinteractions. For ULF wave events with large azimuthal scale lengths anexcellent agreement in the observed wave polarisation ellipse is foundbetween the radar observations and ground-based magnetometer data. Incontrast, for the small scale events, no ground-based magnetic counterpart isobserved. Indeed the data from the two CUTLASS radars seem inconsistent, andeach radar must be interpreted separately, as the spatial resolution of theradars is sufficient to resolve the wave characteristics along the radarbeams, but insufficient to resolve the wave characteristics across the beams.A high azimuthal wave number (m) wave with a period of 300 s andm~−60 is observed to occur over Svalbard at ~14:00magnetic local time. This confirms the existence of waves driven bywave-particle interactions with trapped particle populations in the outermagnetosphere. A comparison of the observed wave characteristics withprevious, lower latitude, observations suggests that these high latitudewaves have a similar azimuthal scale size to those generated in the innermagnetosphere; the azimuthal wave number of −60 observed in the present studyis comparable to previous values of −20– −50, but suggests an increase ofm with latitude. A similar energy source in drifting protonpopulations is also suggested, but with lower characteristic proton energiesof 10 keV implicated at high latitude, compared to the 20–60 keV energiesinvoked for previous lower latitude observations

Bistatic observations of large and small scale ULF waves in SPEAR-induced HF coherent backscatter