Auroral-zone geomagnetic micropulsations with periods of 5 to 30 seconds

Abstract

Observations of geomagnetic micropulsations with periods of 5 to 30 seconds were carried out for a year at College, Alaska. The average activity of micropulsations in the auroral zone was 4.5 times that in the middle latitudes. The average amplitude of the activity in Alaska maximized at about 0.65 γ near 0600 LMT; the minimum of 0.24 γ occurred at about 1900 LMT. There was a general association of micropulsations with the magnetic index K. Empirical relationships of magnetic pulsations with auroral coruscations of 3914 A emission, auroral ionospheric absorption, and electron bremsstrahlung were mentioned. Micropulsation storms are associated with negative bay disturbances and are related to auroral-zone electron bremsstrahlung increases as well as ionospheric absorption phenomena. The average field pulsation amplitudes maximize at the outset of such disturbances at the first indication of a rapid increase in the ionospheric current. The gross current systems measured as negative bays in H reach a maximum value more slowly than the pulsations. The electron bremsstrahlung and ionospheric density enhancements gradually maximize later in the storm development when the position of the gross current system has extended close to the observing station. All evidence seems to indicate that the micropulsation storms result from an ionospheric current system set up at times of primary electron bombardment.