Propagation of Pi2 pulsations in a dipole model of the magnetosphere

Abstract

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 simulation of the propagation of ULF waves in the dipolar region of the magnetosphere has been developed to study these coupled wave modes. This model includes a height-resolved ionospheric conductivity so that ionospheric fields can be more realistically determined, as well as a direct calculation of ground magnetic fields to compare with ground magnetometers using an inductive ionosphere model. Results from this model show that a plasmaspheric resonance can be set up by waves with periods about 1 min and that field line resonances can be excited both inside and outside the plasmasphere. The use of the inductive ionosphere model leads to the conclusion that even a uniform Hall conductivity can break the dawn-dusk symmetry of the convection pattern. 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.

Signal propagation time from the magnetotail to the ionosphere: OpenGGCM simulation

“…As the waves pass through the plasma sheet boundary layer (PSBL) or near the Earth, they encounter both strong density and field gradients, where the fast compressional mode will covert to the shear Alfvén mode. The fast‐Alfvén mode conversion in the PSBL and the magnetic lobes was also observed in Polar satellite data [ Keiling et al , ] and MHD simulations [ Allan and Wright , ; Lysak and Song , ; Lysak et al , ].…”

A Statistical Study of Pi2 Pulsations Observed in the Upper Ionosphere Using Swarm Magnetic Field Data

“…We found that the B z power is a decreasing function of latitude, whereas B x and B y powers are increasing functions. According to numerical studies of plasmaspheric resonances (Lysak et al, 2015;Teramoto et al, 2011), the compressional wave trapped in the plasmasphere is confined in a dipole latitude rage of −40 • < MLAT < 40 • . The cross phases between B z and H are distributed near 0 • without depending on the latitude of the satellite, whereas the B x − H cross phases are near 0 • in the Northern Hemisphere and about 180 • in the Southern Hemisphere.…”

Anharmonic oscillatory flow braking in the Earth's magnetotail

“…For instance, Lysak et al [2015] have investigated propagation of a damped sine wave with about 1 min period from the near-Earth plasma sheet (X ≈ −10 R E ) down to the low-altitude ionospheric boundary placed at 100 km. They have revealed that ULF waves can propagate through the inner magnetosphere, and a compressional pulse at −10 R E can excite both shear-mode field line resonances and fast-mode plasmaspheric resonances.…”