"Interaction of the solar plasma with hot boundary layers at high latitudes of geomagnetic trap: dynamic transfer processes and acceleration"
Sergey Savin (IKI)
Abstract:
On the basis of recent experimental data we study mechanisms of the plasma penetration into the geomagnetic trap: diffusion, viscosity, pulse penetration of plasma jets and finite-gyroradius
effects. At high latitudes over polar cusps, both from the data and from the modeling, in the regions with minimum in magnetic field magnitude the listed above mechanisms are the most
effective. Gyro-viscous friction of the magnetic field lines at the magnetopause results in a normal stress, which is able to shift the magnetopause position; the ratio of the gyro-viscous and Maxwellian stress is proportional to the bulk flow velocity and to the magnetic magnitude in the minus 3d power that maximizes the action
of the stress at the outer cusp boundary. Similar magnetic-field dependence of the plasma diffusion coefficients, both for resonant interaction of the ions with electrostatic ion-cyclotron waves and for non-resonant interactions with kinetic Alfven waves (cf. percolation), results
in the diffusion through the outer-cusps boundaries, which is strong enough to populate the dayside magnetosphere by the solar
plasma. Exploration of the plasma flow interactions with hot boundary layers at high latitudes of geomagnetic trap demonstrates the importance of the nonlinear interact
ion of the waves, reflected from the boundary, with disturbances of the incident
flow. In the case of the small magnetic forces, interference pattern is
formed, which includes standing wave-packets of electric field. Inertial drift in the inhomogeneous electric fields provides the plasma jet acceleration upon magnetosonic
speed; the jets can carry almost half of the flow momentum. The residual flow in the outer boundary layer decelerates down to Alfvenic
velocity. We present data from Interball-1 and Cluster missions, which demonstrate finite-gyroradius and surface-charge effects at magnetopause, along with a brief retros
pective of the solar plasma penetration through the polar cusps.