A study of dayside auroral bright spots seen by the Viking Auroral Imager

Abstract

Instantaneous Viking optical images at UV Lyman‐Birge‐Hopfield wavelength are used to study the occurrence of dayside auroral bright spots versus the upstream solar wind parameters observed by the IMP 8 spacecraft. A survey study of 68 passes indicates that dayside auroral bright spots are most likely observed in the afternoon sector, most commonly have one to four spots simultaneously, and most commonly are separated by 0.25‐0.75 MLT. They also occur most commonly with the following solar wind conditions: high speed (>500 km/s), low density, B y < 0, and interplanetary magnetic field in the radial direction; but they have no dependence on B z , B x , or solar wind pressure. This suggests that dayside auroral bright spots are caused by alternating field‐aligned current regions that map to plasma vortices formed in the magnetospheric boundary layer by the Kelvin‐Helmholtz instability.