A Possible Explanation of Interhemispheric Asymmetry of Equatorial Plasma Bubbles in Airglow Images

Abstract

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 • N, 77.8 • E, 1.7 • 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.

Stepping Into an Equatorial Plasma Bubble With a Swarm Overfly

“…As a consequence, symmetric EPBs occurrence are usually expected. However, inter-hemispheric asymmetry of the EPB occurrence has been reported in the literature as due to different growth rates between the two hemispheres, due to different ionospheric backgrounds (Dai et al, 2023), or inter-hemispheric differences in the neutral winds during two equinoxes (Hickey et al, 2020;Maruyama et al, 2009;Nishioka et al, 2008), or variation in the height of the ionosphere. Barros et al (2022) reports that, in the Brazilian sector, ∼30% of the nights the EPBs presented an apparent inter-hemispheric asymmetry that is also the case of the considered event.…”