Auroral Characteristics Related to AU&AL Indices

Abstract

Auroral images of the N2 Lyman‐Birge‐Hopfield emissions from Polar Ultraviolet Imager (UVI) for 1.5 years are used to investigate the auroral characteristics related to the AU and AL indices that represent the directly driven and unloading processes in the solar wind‐magnetosphere‐ionosphere coupling, respectively. Findings include: (a) Growing AL mainly relates to the nightside aurora and tends to keep the general auroral morphology. (b) As AU increases, the aurora brightens and expands more globally, especially in the midnight to postmidnight sector. (c) The regional auroral power (AP), equatorward boundary, poleward boundary, and peak intensity change quasi‐linearly with intensifying AU and AL. (d) The rates of change depend on the MLT and AU/AL levels. The same dataset has been used to construct the empirical Feature Tracking of Auroral Precipitation (FTA) model which specifies the global energy flux and mean energy determined by the AE index (FTA‐AE). As an extension of FTA‐AE, the relationships of the auroral emission with the AU&AL indices were derived to construct the FTA‐AU&AL model which specifies a more consistent aurora during different magnetospheric driving modes compared to FTA‐AE. Comparisons of AP from the Defense Meteorological Satellite Program Special Sensor Ultraviolet Spectrographic Imagers (SSUSI) measurements and empirical auroral models show that the FTA‐AE and ‐AU&AL models predicted larger AP than the Fuller‐Rowell and Evans (1987) model and the OVATION‐prime model did. As the activity level increased, all four models tended to underestimate the AP but the FTA APs increased relatively faster and were therefore more consistent with the data.