| It is shown that the interaction of the
interplanetary magnetic field (IMF), when it has southward component, with the
geomagnetic field leads to the formation of an enhanced pressure layer (EPL)
near the magnetopause. Currents flowing on the boundary between the EPL and the
magnetosheath prevent the IMF from penetrating the magnetosphere. However, the
outward boundary of the EPL is unstable. The interchange instability permanently
destroys the EPL. Separate filaments of the EPL move away from the Earth. New
colder plasma of the magnetosheath with a frozen magnetic field replaces the
hotter EPL plasma, and the process of EPL formation and destruction repeats
itself.
The instability increment is calculated for various magnitudes
of the azimuthal wave number, ky, and curvature radius of the
magnetic field lines, Rc. The disturbances with R-1e≤ky≤4R-1e
(where Re is the Earth's radius) and Rc≅Re
are the most unstable.
A possible result of the interchange instability of the EPL
may be patchy reconnection, displayed as flux transfer events (FTEs) near the
magnetopause. |