North-south Asymmetry in Dayside Auroras Associated With Local Sunlight Conditions
Abstract
It is well known that the dayside aurora is closely associated with the coupling of the solar wind and the magnetosphere, whereas the nightside aurora is closely associated with magnetotail dynamics. In the last two decades, large amounts of auroral data have been collected and enabled the discovery of the auroral sunlight effect, in which not just the nightside aurora but also the dayside aurora varies with solar insolation but in the opposite sense - nightside auroras are suppressed in sunlight and dayside auroras are enhanced in sunlight. All previous results were concluded based mainly on optical observations from the Northern Hemisphere (e.g., Polar) and on combined north-south in situ particle measurements (e.g., DMSP). It is not known if the effect of solar insolation exists in the Southern Hemisphere. The present study explores the symmetry and asymmetry of the dayside aurora from the Northern and Southern Hemispheres under sunlit and dark conditions. We analyze a large number of Earth disk images in far ultraviolet (FUV) acquired by the Global UltraViolet Imager (GUVI) on-board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite from 2002 to 2007. It is found that the intensity of dayside aurora, in terms of the energy flux of precipitating electrons, is larger when the hemisphere is in sunlight (solar zenith angle: SZA < 108°) and is smaller when the hemisphere is in darkness (SZA > 108°). This trend is independent of the solar wind driving, suggesting a pure solar insolation effect. Because auroras are mainly produced by electron precipitation, this north-south asymmetry suggests a larger (smaller) field-aligned current flowing out of the sunlit (dark) hemisphere, and suggests a voltage generator in the dayside magnetosphere that produces dayside auroras.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMSM11B3272M
- Keywords:
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- 0310 Airglow and aurora;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 2704 Auroral phenomena;
- MAGNETOSPHERIC PHYSICS;
- 2716 Energetic particles: precipitating;
- MAGNETOSPHERIC PHYSICS;
- 2772 Plasma waves and instabilities;
- MAGNETOSPHERIC PHYSICS