Wave- particle interaction as a general mechanism for magnetosheath flow energy transient dissipation
Abstract
We compare Interball-1, Polar and Cluster data on nonlinear perturbations over outer cusp. Magnetosheath flow interacts with a high-beta cusp through reflected waves, detected as sunward bursts in Poynting flux. The waves have 3- wave phase coupling with both enhanced magnetosheath and local Alfvenic fluctuations. It results in plasma jets, accelerated up to magnetosonic speed, and trigger a cascade-like energy chaotization of up to 40% of the magnetosheath kinetic energy. This striking impulsive momentum loss qualitatively differs from bow shock or reconnection processes. It is followed by decelerated Alfvenic flows; a momentum balance is conserved only on time scales of the Alfvenic flows (1/f ~ 12 minutes). Waves at f ~ 1.3 mHz are capable of synchronizing interactions throughout boundary layers, i.e. being a mechanism for self-organization of fluctuations there. Kinetic energy of the jets substantially exceeds the magnetic energy at magnetopause, which should result in the magnetopause deformation and driven reconnection. Incident `fresh' magnetosheath plasma senses standing electric field wave-trains, in which it is accelerated by inertial drift. Small-scale current sheets with anomalous statistics of field-rotation angles are generated due to opposite drift motion of electrons and ions, which is a feature of intermittent turbulence. We compare the measured spectra of fluctuations with that of a model nonlinear system with the intermittent chaotic behavior. A kind of wave-particle interaction is operating at transient small-scale current sheets with surface charges. At scales of ion gyroradius it infers Hall dynamics, so that electric fields of the surface serves as a mechanism for momentum coupling through the current sheets and leads to acceleration of ions with large (in comparison with the sheet width) gyroradius. At borders of large diamagnetic cavities this mechanism can lead to mass exchange and acceleration/ heating of magnetosheath particles. At the larger scales the transient electric field accelerates (via the inertial drift) incident plasma along magnetopause in the downtail direction. In this way the plasma excess is removed and local mass balance is established at the magnetopause. Work was supported by INTAS grant 03-51-4872.
- Publication:
-
35th COSPAR Scientific Assembly
- Pub Date:
- 2004
- Bibcode:
- 2004cosp...35.2355S