A study of ionospheric absorption in conjugate regions produced by storm sudden commencements and sudden impulses in the geomagnetic field

Riometer data from Syowa, Antarctica, and Reykjavik, Iceland, were analyzed for the occurrence of sudden commencement (sc) and sudden impulse (si) absorption events over a 35-month period (February 1967 to December 1969). The results of this study include the fraction of sc and si that produce ionospheric absorption at L = 6.3, the fraction of sc and si events that show absorption effects in conjugate regions, and the magnetic local time distributions of these events. The occurrence probability for conjugate events, plus other spatial features of these events, suggests a scale size of ∼6 × 104 km for solar plasma at the boundary of the magnetosphere.