Alfven Modulation of Substorm Magnetotail Transport
This work explores the proposition that magnetic field resonances
modulate the evolution of particle and magnetic flux in the Earth's
magnetotail. Coordinated high- and low-altitude measurements during
several substorms show periodic variations of magnetic field, plasma,
and high energy particle flux in the magnetotail with a frequency and
phase that correlate well with those of magnetic field oscillations in
the near-tail and pulsations measured by ground-based stations. The
pulsation's frequency is in the Pc 5 range. The example presented here
occurred during the substorm of May 19-20 of 1996 that was chosen as
the first ISTP/GGS campaign for the ground-based and theory
investigations. These observations complement recent findings of a
correlation between periodic geosynchronous dipolarizations and
nightside pulsations. We discuss the possibility of feedback between
the near-Earth resonant cavity modes and the onset of dipolarizations,
current disruption, and neutral line formation.
Four panels of elevation scan data from the Sondrestrom
incoherent scatter radar showing the evolution of the polar cap and
surge boundaries during a substorm expansion on May 20, 1996. Each
panel shows data in a tangent plane (ground range versus altitude)
in the magnetic meridian.