Global auroral power as an index for geospace disturbances

Abstract

We propose to use global auroral power (in gigawatt) as a new geospace activity index, GAP. The auroral power is inferred from auroral luminosity in the N2 Lyman‐Birge‐Hopfield bands (λ ∼1700 ± 100 Å) observed by the ultraviolet imager on the Polar satellite. We demonstrate, on the basis of one‐day's worth of data, that GAP correlates well with the 1‐min quick‐look auroral electrojet AEQL index (r = 0.85). We also propose a local‐time auroral keogram (LAK) to illustrate dynamic evolution of global auroral energy deposition. The combination of GAP and LAK provides a powerful tool for morphological study of aurora on a global scale. The importance of these new indices is demonstrated by an analysis of substorm onset timing in comparison with the AE index. It is found that the auroral onset often precedes the magnetic onset, indicated by the AEQL index.