A statistical survey of dayside pulsed ionospheric ̄ows as seen by the CUTLASS Finland HF radar

Nearly two years of 2-min resolution data and 7to 21-s resolution data from the CUTLASS Finland HF radar have undergone Fourier analysis in order to study statistically the occurrence rates and repetition frequencies of pulsed ionospheric ̄ows in the noon-sector high-latitude ionosphere. Pulsed ionospheric ̄ow bursts are believed to be the ionospheric footprint of newly reconnected geomagnetic ®eld lines, which occur during episodes of magnetic ̄ux transfer to the terrestrial magnetosphere ± ̄ux transfer events or FTEs. The distribution of pulsed ionospheric ̄ows were found to be well grouped in the radar ®eld of view, and to be in the vicinity of the radar signature of the cusp footprint. Two thirds of the pulsed ionospheric ̄ow intervals included in the statistical study occurred when the interplanetary magnetic ®eld had a southward component, supporting the hypothesis that pulsed ionospheric ̄ows are a reconnection-related phenomenon. The occurrence rate of the pulsed ionospheric ̄ow ̄uctuation period was independent of the radar scan mode. The statistical results obtained from the radar data are compared to occurrence rates and repetition frequencies of FTEs derived from spacecraft data near the magnetopause reconnection region, and to ground-based optical measurements of poleward moving auroral forms. The distributions obtained by the various instruments in di€erent regions of the magnetosphere were remarkably similar. The radar, therefore, appears to give an unbiased sample of magnetopause activity in its routine observations of the cusp footprint.