ALF - A Probabilistic Auroral Location Forecast derived from Far-Ultraviolet Auroral Boundaries and Geomagnetic Activity

Using auroral boundaries determined from far ultraviolet images of the aurora (Chisham et al., 2022), we have examined auroral occurrence with respect to magnetic latitude, local time and the Kp index. Our results show that auroral occurrence is highly correlated (R²>90%) with Kp between values of 0o and 5o. We use linear fits between occurrence and Kp to build a probabilistic Auroral Location Forecast (ALF) which gives the likelihood of the aurora occuring at a given magnetic latitude and local time for any level of Kp. The model includes both correlated relationships between Kp and occurrence at low latitudes and anti-correlated relationships between Kp and occurrence at high latitudes, enabling the model to replicate behaviour expected within the expanding-contracting polar cap paradigm. The model also shows higher variability in the location of the auroral boundary close to the interface between the upward Region 2 currents and downward Region 1 currents. Validation of the model returns high Brier Skill Scores for both the range of Kp used in the model creation (Kp=0 – 5, Brier Skill Score = 0.569) and the range unseen by the model (Kp=6 – 9, Brier Skill Score = 0.532) indicating that the model is skillful in predicting the location of the aurora. The results of our analysis and outputs of ALF may be of interest to space weather professionals and ‘aurora chasers’ in determining the likelihood of aurora being present, particularly when coupled with forecasts of the Kp index.