This animation illustrates how magnetic reconnection in the magnetotail triggers the onset of substorms. THEMIS observations for the first time showed that the onset of a substorm follows a specific pattern: tail reconnection is followed by rapid aurora brightening and extension toward the poles. The result is a redistribution of the electrical currents flowing in near-Earth space.
Posted in 'Watching the northern lights form' at http://www.sciencenews.org/view/generic/id/34425/title/Watching_the_northern_lights_form
Video courtesy of Walt Feimer NASA,GSFC