Auroral Phenomena in an Integral-Invariant Coordinate System

Isochasms of auroral phenomena, when plotted in geomagnetic dipole coordinates, are approximately circular and centered on the poles. However, a significant longitude dependence remains. The B, L and R, λ integral-invariant coordinate systems, originated by Mcllwain, have proved successful in ordering satellite measurements of the radiation belts. The spatial occurrence of aurora has been compared with isolines of L but the R, λ system appears better suited to such plots. The evidence for a close relationship between auroral absorption and electron precipitation from the radiation belts is reviewed, and in accordance with this relationship it is shown that the R, λ coordinate system provides a convenient longitude-independent representation of the northern auroral absorption zone.