This report deals with micropulsation data measured at Fort Churchill and at the near-conjugate stations of Byrd and Great Whale River during the conjugate-point experiment by Stanford University and Pacific Naval Laboratory. All three stations are in the auroral zones; and the data, though discontinuous, cover the period from 1961 to 1963.On the assumption that near-coincidence in time of events should be displayed at two conjugates, attention has been concentrated on the times of occurrence of the relatively numerous polar sudden commencements which often introduce the negative bays. There is a striking and very persistent diurnal variation, with maximum occurrence in the hours 03 to 04 G.M.T., which shows at all three stations, but most clearly at the two conjugates.A small time difference, of about one minute on the average, is apparent between events measured at Byrd and those at Great Whale. There is a tendency for the events to be preceded by a quiet period, and they correspond to sudden changes shown on local magnetograms, and lead to a similar diurnal variation of the magnetic elements H, D, and V. A similar pattern appears in the sudden changes of ionospheric absorption shown on the riometer records from Cape Jones, which is about 180 km from Great Whale Rive; but adequate data for individual time differences are lacking. The coincidence of nighttime active auroras and micropulsation polar-storm commencements measured at the same station seems to be very close. The quiet daytime auroras often show coincident pulsations of light intensity of the same period as the regular (Pc type) micropulsations.
Correction [to “On the poleward expansion of ionospheric absorption regions triggered by sudden commencements of geomagnetic storms”]
