Micropulsations at Near Conjugate Stations in the Auroral Zones and their Association with Other Ionospheric Phenomena

Abstract

After a short and incomplete review of previous work, this report deals with the results of the joint operation with Stanford University at Fort Churchill, Great Whale River and its near conjugate at Byrd Station.

On the assumption that data recorded at conjugate points will be very similar and will occur nearly simultaneously, attention has been focused on the micropulsation and magnetograph “events” which occur quite frequently and introduce Birkeland’s Polar Elementary Storms. These have adequately sudden commencements to enable them to be timed with an accuracy of about 1/2 minute for a single micropulsation event. These events are preceded by a quiet interval and followed by bays, or DP’s.

There is a pronounced difference between the daytime and the nighttime regimes, records of the former often being of regular (Pc) shapes and the latter nearly always of irregular shape (Pt) with components of much higher frequency (riders). The duration of these riders is seldom longer than eight minutes. Simultaneous auroral events and activity also show similar differences between the daytime and nighttime regimes and the evidence suggests the same is also true of ionospheric absorption and hiss.

All these ionospheric events occur simultaneously when measured at the nearconjugate sites of Great Whale and Byrd and sometimes also at Churchill. They occur most frequently in the two hours ending 04 G.M.T. which is not far from geomagnetic midnight at Great Whale. The events can also be recorded on sensitive micropulsation instruments in middle latitudes, presumably as “leakage” currents from the auroral electrojets. Those which include the higher frequency riders, which also appear nearly simultaneously with the negative H events in the auroral zones, have a pronounced maximum of occurrence at Victoria about midnight local mean time. The events can also sometimes be recognized on mid-latitude magnetograms as small perturbations if it is known from other sources when to look for them.

It is suggested that the opportunity exists of examining in more detail the relative importance of local mean and geomagnetic time in the incidence of these events in different longitudes around the globe and the difference in form between daytime and nighttime events.

In the frequency range of 0.005 to 3 cps, with which this report is almost entirely concerned, the balance of evidence is that conjugate points in the auroral zones are of fleeting duration in the sense that points which are conjugate one day are not necessarily conjugate next day or next week.

It seems that the origin of the events lies within the magnetosphere, but a direct relation with fluctuations in the solar wind cannot be excluded.