DIPOLE-FIELD TYPE MAGNETIC DISTURBANCES AND AURORAL ACTIVITIES
The characteristics of the magnetic field components at Agincourt have been calculated for a current system produced by an electric dipole located in the region of auroral activity near Ottawa. It is noted that, irrespective of the orientation of the dipole, the horizontal magnetic field component rotates in the clockwise and anticlockwise senses for motion of the dipole towards the east and the west respectively, when the dipole is situated in the north half of the sky as seen from the observing station.Next, the magnetograms obtained at Agincourt have been studied at those times of the night when auroral activity was recorded in the all-sky camera photographs at Springhill near Ottawa. It is noted that the horizontal magnetic field describes a loop during a particular phase of auroral activity because of its gradual growth and decay. The distributions of clockwise and anticlockwise rotations with respect to local time are found to be very similar in many respects to those of auroral motions to the east and west respectively. The sense of rotation of the loop is predominantly anticlockwise in the early part of the night and clockwise in the late hours of the night.It is found that eastward and westward orientations of the dipole are the most probable ones. The direction of movement and the initial location of the predominant auroral form in the sky are found to tally well with those of the dipole deduced from a study of the magnetograms.It seems that there is a time sequence relationship between successive phases of auroral activity and changes of characteristics of the loops described by the horizontal magnetic field vector. The area of a loop and the maximum magnitude of the field vector in the loop appear to be related to the brightness and horizontal extent of the auroral forms.