SIMULTANEOUS OBSERVATION OF A TRAVELING VORTEX STRUCTURE IN THE MORNING SECTOR AND A FIELD LINE RESONANCE IN THE POSTNOON SECTOR

Radar observations suggesting ULF field line resonances impulsively excited via a cavity or waveguide mode were obtained simultaneously in the dawn (Bistatic Auroral Radar System (BARS)) and postnoon (Sweden and Britain Radar-Auroral Experiment (SABRE)) sectors. The primary data used to study this event are from both the European Incoherent Scatter magnetometer cross and Subauroral Magnetometer Network magnetometer arrays in the postnoon sector and from the Canadian Auroral Network for the Origin of Plasmas in the Earth's Neighborhood Program Unified Study (CANOPUS), MAgnetometer, RIometer and tellurics Array (MARIA), the GOES 7 magnetometer, and the neural network classification of Defense Meteorological Satellite Program (DMSP) particle data in the dawn sector. In the postnoon sector (Scandinavia) a decaying field line resonance was observed following a more complicated initial interval. The resonance period was 326 s (3.07 mHz). However, in the dawn sector the response was dominated by the initial interval in which the characteristics of a traveling vortex system were observed. The subsequent disturbance in this sector was of lesser amplitude and without discerned pattern. The field-aligned current(s) of the traveling vortex structure was (were) at about 65° Eccentric Dipole Field Line (EDFL) latitude (approximately 68° International Geomagnetic Reference Field (IGRF)). The DMSP neural network data, however, indicate this position to have been well within the magnetosphere. GOES 7 was on a field line which was connected to the ionosphere near the MARIA meridian line at about 62.5° EDFL latitude (approximately 65.5° IGRF), just equatorward of the traveling vortex structure. It observed a magnetic disturbance which was initially driven and followed directly by a damped sinusoid signature of the azimuthal component. The frequency during this decay was 4.45 mHz (225-s period). Values of ∑p, the height-integrated Pedersen conductivity for both the postnoon and GOES 7 damped segments were deduced. These were low, particularly if the disturbances were in the second harmonic along the field line as suggested by GOES 7 data, and perhaps imply an additional loss mechanism. Although substantially understood, this pulsation event had distinctly different characteristics in the two time sectors and displayed many puzzling features. In particular, it was significantly more complicated than our initial anticipation of global excitation of field line resonances via a cavity or waveguide mode.