Storm after-effects observed at Ushuaia and Kerguelen

D-region disturbances have been detected at mid-latitudes after intense magnetic storms by means of a wide range of radiowave signals. Two different mechanisms have been suggested to account for these storm ‘after-effects’: one implies precipitation of energetic electrons from the radiation belt; the other, transport of neutral constituents from the auroral zones.This paper presents observations of abnormal enhancements of ionospheric absorption arising after two major magnetic storms occurring in March and April 1976. The measurements were made at Ushuaia (54.8°S, L = 1.7) and at Kerguelen (49.4°S, L = 3.7). The former were obtained by means of the pulse reflection method (A1) at MF and the latter by the riometer technique. It is shown that electron precipitation can explain the effects observed at Kerguelen but not those at Ushuaia which also depart significantly from the ‘winter anomaly’ trend observed at that site. The abnormal ionization at Ushuaia is attributed to transport from the southern auroral zone.