A STUDY OF AURORAL MOTIONS FROM ALL-SKY CAMERA RECORDS

Abstract

A study of horizontal motions of visual aurorae as recorded by a 35-mm all-sky camera at Springhill (geographic 45.2 °N., 75.5 °W.; geomagnetic 56.5 °N., 6.9 °W.) near Ottawa has been carried out. The number of occurrences of motions in all the four geomagnetic directions, east, west, north, and south appears to reach its peak within a range of speed from 0 to 150 m/sec and tends to decrease with increase in speed. Very large speeds seem more frequently to be associated with motions to the west and to the south. The distribution curve of speed with the time of night appears to have two peaks, one before and another after midnight, in all the four cases. Auroral motion is predominantly westward in the early part of the night and eastward in the late hours of the night. The reversal of motion from westward to eastward direction seems to be a systematic process, the declining and inclining portions of the two curves as a function of time meeting each other somewhat before local midnight.Auroral speeds either along or perpendicular to geomagnetic parallels of latitude increase nearly linearly with the horizontal and vertical components of the magnetic disturbance vector.