Ion-driven instabilities in the solar wind: Wind observations of 19 March 2005.
Intervals of enhanced magnetic fluctuations have been frequently observed in the solar wind. But it remains an open question as to whether these waves are generated at the Sun and then transported outward by the solar wind or generated locally in the interplanetary medium. Magnetic field and plasma measurements from the Wind spacecraft under slow solar wind conditions on 19 March 2005 demonstrate seven events of enhanced magnetic fluctuations at spacecraft-frame frequencies somewhat above the proton cyclotron frequency and propagation approximately parallel or antiparallel to the background magnetic fieldBo. The proton velocity distributions during these events are characterized by two components: a more dense, slower core and a less dense, faster beam. Observed plasma parameters are used in a kinetic linear dispersion equation analysis for electromagnetic fluctuations atk x Bo= 0; for two events the most unstable mode is the Alfvén-cyclotron instability driven by a proton component temperature anisotropy T⊥/T||> 1 (where the subscripts denote directions relative toBo), and for three events the most unstable mode is the right-hand polarized magnetosonic instability driven primarily by ion component relative flows. Thus, both types of ion anisotropies and both types of instabilities are likely to be local sources of these enhanced fluctuation events in the solar wind.
Space Science Institute Boulder Colorado USA.
S Peter
SP
Gary
Goddard Planetary Heliophysics Institute University of Maryland College Park Maryland USA; NASA Goddard Space Flight Center Greenbelt Maryland USA.
Lan K
LK
Jian
Southwest Research Institute San Antonio Texas USA.
Thomas W
TW
Broiles
Harvard Smithsonian Center for Astrophysics Cambridge Massachusetts USA.
Michael L
ML
Stevens
Space Science Institute Boulder Colorado USA.
John J
JJ
Podesta
Department of Atmospheric, Oceanic, and Space Sciences University of Michigan Ann Arbor Michigan USA.
Justin C
JC
Kasper
instabilities; solar wind