Parallel electric fields in dispersive shear Alfven waves in the dipolar magnetosphere

Existing theories do not explain large parallel electric fields that are as sociated with keV electron precipitation in auroral arcs. The MHD electron response results in an electrical conductivity in the low altitude magnetos phere that is two orders of magnitude greater than is required. We suggest a new mechanism for forming parallel electric fields based on a nonlocal el ectron response to standing shear Alfven waves on dipole magnetic fields. E lectron trapping is the primary cause of a significant reduction in the col lisionless electron conductivity and consequent enhancement of parallel ele ctric fields in the 1 - 4 mHz frequency range.