Observations of differences between regions of current flowing into and out of the ionosphere

Abstract

A correlative study of field‐aligned currents, upflowing ions and electrostatic shocks has been made using data from the S3‐3 satellite. Upflowing ions with pitch angle distributions that are peaked at an angle to the magnetic field ("conics") are observed in all auroral current regions, but upflowing ions with distributions peaked along the field ("beams") are seen only in upward current regions. Thus, indirect evidence for parallel electric fields is seen in regions of upward current, but not in regions of downward current. Electrostatic shocks are usually observed in the current sheet associated with the polar cap convection boundary. In the evening, when this current is upward, shocks are largest. Indirect evidence for parallel electric fields is seen in regions of upward current, but not in regions of downward current. The altitude and magnetic local time dependence of upflowing ions and electrostatic shocks may be explained by the physical consequences of the differing particle populations carrying current into and out of the ionosphere. The data suggest that current‐driven turbulence plays a crucial role in energizing particles in the auroral zone.