A STUDY OF DAYSIDE AURORAL BRIGHT SPOTS SEEN BY THE VIKING AURORAL IMAGER

Instantaneous Viking optical images at UV Lyman-Birge-Hopfield wavelen gth are used to study the occurrence of dayside auroral bright spots v ersus the upstream solar wind parameters observed by the IMP 8 spacecr aft. 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 separate d by 0.25-0.75 MLT. They also occur most commonly with the following s olar wind conditions: high speed (>500 km/s), low density, B-y < 0, an d 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 magnetospher ic boundary layer by the Kelvin-Helmholtz instability.