COMPARISON OF BOUNDARIES FOR HF AURORAL BACKSCATTER AND VHF SCINTILLATION

A study is described of the equatorwards boundary of high-latitude ion ospheric irregularities using measurements obtained by two different e xperimental techniques. Auroral traces observed on backscatter ionogra ms from an HF radar have been used to identify the boundary of the dec ametre scale-size irregularities responsible for the coherent backscat ter. Simultaneous observations of scintillation on the 150 MHz signals from NNSS satellites have enabled the boundary for irregularities in the sub-kilometre scale regime to be located. Comparisons of the resul ts from the two techniques indicate that reconciliation between bounda ry positions can be made in only about 50% of the cases considered. In general the scintillation boundary lies on average well polewards of that identified by the HF radar, suggesting that caution should be exe rcised in the mapping of irregularity boundary positions.