Propagation of BBF Driven Pi1/2 Waves to the Inner Magnetosphere and the Ionosphere
Monday, 15 December 2014: 3:28 PM
Localized fast flows that impinge on the inner magnetosphere from the plasma sheet are observed to oscillate on time scales of minutes. The compression ahead of these flows will launch fast mode waves, while the velocity shears at the edges of these flows directly excite shear Alfvén waves. These waves, which are coupled by gradients in the Alfvén speed, have been suggested as a source for the Pi1 and Pi2 waves that are observed at both high and low latitudes in the ionosphere. A new three-dimensional model for the propagation of ULF waves in the dipolar region of the magnetosphere has been developed to model these coupled wave modes. This model includes a height-distributed ionospheric conductivity so that ionospheric fields can be realistically modeled, as well as a direct calculation of ground magnetic fields that can be compared with ground magnetometers. Results from this model show that a plasmaspheric resonance can be set up by waves with periods about 1 minute, and that field line resonances can be excited both inside and outside the plasmasphere. Waves from a source at 10 Earth radii reach the ionosphere with time delays between high and low latitudes of tens of seconds, with implications for the timing of substorm phenomena observed by spacecraft and by ground magnetometers and radars.