Asymmetric auroral intensities in the Earth's Northern and Southern hemispheres

• Published in: Nature (London) Vol. 460; no. 7254; pp. 491 - 493
• Main Authors: Laundal, K. M, Østgaard, N
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 23-07-2009; Nature Publishing Group
• Subjects: Asymmetry; Auroras; Charged particles; Comparative analysis; Earth; Earth, ocean, space; Electric properties; Exact sciences and technology; External geophysics; Hemispheres; Humanities and Social Sciences; Ionospheric electron density; letter; Longitude; Magnetic fields; Magnetosphere; multidisciplinary; Photoionization; Physics of the magnetosphere; Satellites; Science; Science (multidisciplinary); Spots; Trapped particles; Norway; intensity; magnetic field; Southern Hemisphere; Field line; Aurorae; Northern Hemisphere; IMAGE satellite; Magnetic line; Charged particle; asymmetry; Auroral activity
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature08154

It is commonly assumed that the aurora borealis (Northern Hemisphere) and aurora australis (Southern Hemisphere) are mirror images of each other because the charged particles causing the aurora follow the magnetic field lines connecting the two hemispheres. The particles are believed to be evenly distributed between the two hemispheres, from the source region in the equatorial plane of the magnetosphere. Although it has been shown that similar auroral features in the opposite hemispheres can be displaced tens of degree in longitude and that seasonal effects can cause differences in global intensity, the overall auroral patterns were still similar. Here we report observations that clearly contradict the common assumption about symmetric aurora: intense spots are seen at dawn in the Northern summer Hemisphere, and at dusk in the Southern winter Hemisphere. The asymmetry is interpreted in terms of inter-hemispheric currents related to seasons, which have been predicted but hitherto had not been seen.