Conjugate observations of an electron precipitation event associated with the sudden commencement of a magnetic storm

The ionospheric absorption resulting from excess ionization in the lower ionosphere by energetic electrons precipitated during the sudden commencement of 0555 UT, August 11, 1967, has been observed by riometers. The data from Kotzebue, Alaska, and its conjugate at Macquarie Island demonstrate the close conjugacy of precipitation. An Alaskan north-south chain of riometers shows that the peak sc flux occurred at about L = 6.5. Taken together, the data indicate that the sc electrons are precipitated from the dayside trapping region by some pitch angle diffusion mechanism.