A possible explanation of interhemispheric asymmetry of Equatorial Plasma Bubbles in airglow images

Equatorial plasma bubbles resulting from equatorial spread F are well known to be aligned along the Earth's geomagnetic fields. During the geomagnetic storm on 17 March 2015, all-sky airglow observations from Tirunelveli (8.7 degrees N, 77.8 degrees E, 1.7 degrees N dip latitude) showed an apparent interhemispheric asymmetry in the tilt of the equatorial plasma bubbles. In this work we further investigate this case and provide a possible explanation for the asymmetry. We suggest that a variation in the altitude of the airglow layer across the image can cause the observed asymmetry. If the airglow layer is at a higher altitude in the northern portion of the image, then this would explain the observed asymmetry. This variation in the airglow layer can be caused by a variation in the height of the ionosphere. We show through modeling and ionosonde observations that it is likely that there is a variation in the airglow altitude within the field of view of the images on this night.