Particle and field data from a 4100-km-altitude satellite pass through a 1.3-mHz field line resonance, identified by ground-based optical, magnetic and radar signatures, are compared with results from a two-fluid MHD-gyrokinetic simulation, including dispersively and resistively sustained parallel electric fields. It is shown that the resonance powers spatially adjacent up- and down-going suprathermal-electron fluxes, a 10-km-scale auroral arc and an imbedded electrostatic shock. Alfv¿n wave dispersion and anomalous plasma resistivity are key elements in the interpretation of the event. ¿ 1998 American Geophysical Union