The Big Picture: Synoptic Views of Auroral Particle Precipitation

Global images and composite views of auroral energy deposition into the ionosphere come from UV imagers (such as on Polar) and from low-altitude polar orbiting satellites, such as the DMSP series. The advantages and disadvantages of each technique are briefly reviewed. Then a series of contrasts in the behavior of particle precipitation are drawn. These are (1) Ion versus electron precipitation; (2) Diffuse auroral precipitation versus discrete auroral precipitation; (3) Dayside versus nightside precipitation; (4) Sunlit versus darkness; and (5) Geomagnetically active times versus quiet times. For example, ion precipitation is supplies approximately 20 percent of the precipitating energy to the ionosphere, declining during times of increasing geomagnetic activity. The relative importance of diffuse versus discrete aurora is still not adequately investigated, but (despite occasional guesses to the contrary) the two appear to be roughly comparable in precipitating energy input to the atmosphere.