Earth’s aurora: north–south asymmetry

New evidence suggests that the commonly held idea that the aurora borealis (in the Northern Hemisphere) and aurora australis (in the south) are mirror images of each other is not always the case. Aurora do tend to occur at the same time in northern and southern polar regions at locations connected by geomagnetic field lines, a connection that might be expected to link patterns, positions and timing of the two aurora. On 12 May 2001 two Earth observation spacecraft — IMAGE and Polar — were well placed to observe the two poles simultaneously. The resulting images have now been analysed and they provide clear evidence that the auroras can be asymmetric. The asymmetry may be caused by inter-hemispheric currents predicted to arise from conductivity differences, but not previously demonstrated.