Variations in the dayside and nightside auroral luminosity during the substorm activity on October 15, 1986 are examined using images obtained by the ultraviolet (UV) imager on board the Viking spacecraft. It is observed that the intensity and dynamic behavior of the localized auroral emissions around the 14 MLT sector can be comparable to that found for nightside discrete arc structure seen during auroral-breakup conditions. For the event studied in this paper, spatial periodicities in luminosity are observed in both the dayside and nightside auroral oval during substorm activity with the azimuthal separation between bright spots on the dayside being approximately 1.5 hours of MLT in the postnoon quadrant and approximately 0.5 hour of MLT in the midnight sector. However, we have no direct evidence that these groups of spots are necessarily linked causaly. We suggest that such features could be a manifestation of a Kelvin--Helmholtz instability located at the sites of a velocity shear zone. ¿American Geophysical Union 1987