Auroral particle precipitation and Birkeland Currents

Correlated measurements that provide information on Birkeland (field aligned) currents are reviewed. Because of the obvious importance of field‐aligned electric fields with regard to Birkeland currents, the last section of the paper is devoted to a presentation of recent data on the observations of field‐aligned auroral electron fluxes and monoenergetic peaks in the spectrum. Experimental data cannot yet define the overall magnetospheric pattern of the Birkeland current system. The largest body of data regarding these currents comes from polar‐orbiting satellites. These data indicate that current sheets are associated with auroral displays and that field‐aligned electron fluxes on the order of 1‐keV energy are significant charge carriers for the conventional current out of the atmosphere. Rocket observations verify that electrons responsible for the production of auroral forms carry a significant fraction of the current necessary to produce local magnetic effects that require Birkeland currents for their explanations. There are a few measurements that suggest that the return current might be carried by low‐energy electrons (less than a few hundred electron volts) streaming out of the atmosphere.