Simple Pi burst micropulsation events and associated aurora at two sites in Alaska

Type Pi magnetic-field pulsation bursts were selected for which the associated aurorae were relatively simple and stable and occurred in the ionosphere between College and Fort Yukon in alaska. Power spectral-density traces for College and Fort Yukon H and D were computed and were studied relative to the aurora and to more complex events presented in earlier studies. The power spectral-density traces associated to simpler aurora were found to be consistent with the assumption of simpler 3-dimensional current systems as generators of the Pi waves. The spectra of associated precipitation pulsations had a peak near 10 mHz in common with the magnetic field spectra in all events, and also near 3 mHz in one event. The precipitation pulsations at 3 and 10 mHz may have enhanced the magnetic spectra at those frequencies through modulation of the ionospheric resistance to the current. (author)