Riometer and HF radar signatures of polar patches

Polar patch was the name given originally to a spatially limited enhancemen t of the 630-nm emission observed in the dark polar cap. More recently, the term has been applied to related phenomena observed by other experimental techniques. The interrelationship between patches observed by differing met hods has yet to be determined fully. In this paper the signatures of a seri es of polar patches observed by Halley HF radar and the South Pole broad-be am and imaging riometers are presented. Most frequently, the HF radar patch signature immediately precedes that of the riometer polar patch signature. The interpretation is that the leading edge of the electron concentration structure that forms the patch is steeper than its trailing edge. On a few occasions, HF radar polar patch signatures coincide with the trailing edge of riometer patches and sometimes are seen throughout the riometer patch. H alley digital ionosonde data are used to show that riometer patches are mor e common over South Pole when the maximum I; region plasma concentration is considerably in excess of 5 x 10(11) m(-3), which often occurs in the afte rnoon plasma convection cell.