THE RELATIONSHIP BETWEEN ELECTROSTATIC SHOCKS AND KINETIC ALFVEN WAVES

Auroral satellites and sounding rockets frequently observe large elect ric fields perpendicular to the magnetic field that have a narrow scal e length perpendicular to the magnetic field if they are interpreted a s spatial structures. These fields have been variously attributed to e lectrostatic shock structures or to kinetic Alfven waves. These two mo dels can be distinguished by considering the ratio of the magnetic fie ld perturbation to the electric field. This ratio is calculated within the context of the electrostatic approximation, the fully kinetic Alf ven wave dispersion relation considered by Lysak and Lotko [1996], and the cold fluid model including ionospheric reflection presented by Ly sak [1991, 1993]. Results for this model show that the ratio of the el ectric to magnetic field is not always equal to the Alfven speed, espe cially for structures that are very narrow in the direction perpendicu lar to the magnetic field. These narrow structures have electric field s that are enhanced with respect to the Alfvenic value, and thus may a ppear as electrostatic.