Dynamics of long-period magnetic activity and energetic particle precipitation during the May 15, 1997 storm

Abstract

The large-scale behavior of quasi-steady magnetic activity and energetic particle precipitation and their variations in the nominal Pc5-6/Pi3 band (1.7– 10 mHz ) during the main phase of the intense magnetic storm on May 15, 1997, is studied using data from an array of magnetic and riometer stations in the Northern Hemisphere. The global azimuthal structure of magnetic and cosmic noise absorption disturbances at ∼64° geomagnetic latitude is revealed with the help of MLT-UT diagrams. The ionospheric westward electrojet intensifies in the morning sector and the eastward electrojet intensifies in the evening sector. Intense storm-related ULF magnetic activity is evident in two regions: in the early morning hours and in the evening sector. In the dawn sector, the westward electrojet intensification and ULF magnetic pulsations are accompanied by concurrent variations of cosmic noise absorption. In the dusk sector, where observations at two magnetic stations with small separations (<10°) are available, the data indicate small-scale structure of storm-related Pi3 pulsations with longitudinally sunward propagation, as might be expected according to the injected proton drift. The small-scale meridional pattern of ULF-modulated electron precipitation during the substorm interval as determined from the IRIS riometer in Scandinavia indicate poleward propagation in the dawn sector. The results suggest that the physical mechanism of long-period magnetic disturbances observed during the main phase of a magnetic storm is different from common dawn Pc5 pulsations and is related to the injection of energetic electrons and protons into the early morning and dusk sectors of magnetosphere, correspondingly. This difference is important for the modeling of relativistic electron energization by ULF waves.