Diagnostics of Magnetic Substorms Using Satellite Observations of Magnetic Pulsations

Abstract

Abstract : This project has demonstrated that one class of magnetic pulsations known as stormtime Pc 5 waves is correlated with substorm onsets. Stormtime Pc 5 waves observed by geostationary satellites in the afternoon sector is characterized by oscillations of magnetic field with a period from 2 to 10 minutes, easily detected by magnetometers on communication or weather satellites. The estimated substorm onset times are found to be within 20 minutes of the actual substorm onset times. Geosynchronous satellites in the afternoon sector would detect these low frequency wave events about 2-4 hours after a substorm onset occurring at local midnight. The delay time depends on the propagation velocity, which varies from a few km/s up to 50 km/s. The disturbed region of a stormtime Pc 5 event has a longitudinal extent varying between 30 and 90 degrees. The study shows that stormtime Pc 5 waves have a wave amplitude confined with about 10 deg from the magnetic equator. The propagation velocity is found to increase with wave frequency and with the magnetic field inclination angle. Comparison of the statistical properties of stormtime Pc 5 waves with theoretical calculations of propagation velocity suggests that the propagation velocity of stormtime Pc 5 waves agrees better with the perpendicular group velocity of drift mirror mode. The propagation velocity of stormtime Pc 5 waves appears to be mainly determined by wave parallel wavelength, which is in turn determined by the inclination angle or the magnetic field topology. The obtained results about the propagation properties of magnetic pulsations during storm times is important for the satellite operation since it can be used to predict the plasma environment a synchronous satellite might encounter.