Electrostatic Solitary Waves Associated with Magnetic Reconnection

Y. Omura (Radio Science Center for Space and Atmosphere, Kyoto University)

Electrostatic solitary waves (ESW) are frequently observed 
in the plasma sheet boundary layer of the Earth's magnetotail, as
reported by GEOTAIL and other recent spacecraft.  Particle simulations
have clarified that ESW are generated as a result of coherent nonlinear
evolution of beam-plasma instabilities such as electron two-stream
instability,  bump-on-tail instability, and Buneman instability.  One of
the possible mechanisms of electron beam formation is acceleration of
electrons in the process of magnetic reconnection. Meandering motion of
the current sheet can also cause an effective induction electric field,
resulting in the localized acceleration of electrons and ions in the
opposite directions. Although the Buneman instability diffuses the
accelerated electrons, a substantial part of the thermal electrons are
not trapped by large electrostatic potentials formed by the instability,
traveling freely along the magnetic field line as an electron beam. They
subsequently cause the bump-on-tail instability, interacting with the
unperturbed background plasma.  We review the observations, simulations,
and theories of ESW, and discuss the implication of plasma wave
observations in the study of magnetic reconnection.