The E-bin Model: an AE-based Empirical Model of Auroral Precipitation with a New Cumulative-energy Binning Method

Abstract:

A new auroral precipitation model was constructed based on 1.5 years of POLAR ultraviolet imager (UVI) data and parameterized by the Auroral Electrojet (AE) index. The equatorward and poleward boundary in each magnetic local time (MLT) bin was identified, and 19 cumulative energy bins, from 5%-95%, were identified and used to track the latitudinal distribution of the aurora. The model finds a nearly linear relationship between boundary locations and AE in each MLT sector, with the aurora getting wider and moving more equatorward on the nightside, and becoming narrower and moving only slightly equatorward on the dayside. The modeled peak intensity of the aurora is also almost linearly related to AE, with the peak in intensity moving from pre-midnight to post-midnight as activity increases. Field-aligned current sheet-like structures are visible around midnight in the model from 350 nT < AE < 600 nT. The nightside-to-dayside ratio of hemispheric power (HP) increases from ~1.3 to ~3.4 as AE grows to 650 nT and stays around 3.4 above. Comparisons between measurements of the aurora on 17 March 2013 from the Special Sensor Ultraviolet Spectrographic Imagers (SSUSI) and the results from three models (Fuller-Rowell & Evans (1987) model, OVATION prime (Newell et al., 2014), and the E-bin model) showed that the E-bin model specified the most confined patterns with the highest energy flux, agreed with the spatial and temporal evolution of SSUSI energy flux to a high degree, and predicted HP better during higher activities (SSUSI HP > 20 GW).