ELECTRON INERTIAL EFFECTS ON GEOMAGNETIC-FIELD LINE RESONANCES

A three-dimensional compressible resistive magnetohydrodynamic simulat ion code, with inclusion of the fully generalized Ohm's law, has been developed to study the nonlinear evolution of field line resonances in Earth's magnetosphere. A simple Cartesian box model of an inhomogeneo us plasma with straight geomagnetic field lines is used, and the Alfve n velocity increases monotonically from the magnetopause boundary laye r toward Earth. A monochromatic fast mode compressional oblique wave i s applied from the direction of the magnetopause boundary layer, pumpi ng energy into the magnetosphere. The fast mode wave, while propagatin g toward Earth, is partially reflected at the turning point (located a t radial distances between 8 and 10 R(E) in the equatorial plane) and then couples to shear Alfven waves, leading to the formation of large- amplitude field line resonances near Earth. The field line resonances are observed to narrow to several electron inertia lengths within seve ral wave periods of the driver wave, and electron inertial effects bec ome important at this stage. Final profiles near the resonance are ver y similar to Airy functions, indicating that electron inertial effects become important before possible nonlinear effects. The electron iner tial effects lead to oscillating parallel electric field which might b e potential accelerators for electrons in some types of auroral arcs.