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The aurora is a readily visible phenomenon of interest to many members of the public. However, the aurora and associated phenomena can also significantly impact communications, ground-based infrastructure, and high-altitude radiation exposure. Forecasting the location of the auroral oval is therefore a key component of space weather forecast operations. A version of the OVATION-Prime 2013 auroral precipitation model (Newell et al., 2014, https://doi.org/10.1002/2014sw001056) was used by the UK Met Office Space Weather Operations Centre (MOSWOC). The operational implementation of the OVATION-Prime 2013 model at the UK Met Office delivered a 30-min forecast of the location of the auroral oval and the probability of observing the aurora. Using weather forecast evaluation techniques, we evaluate the ability of the OVATION-Prime 2013 model forecasts to predict the location and probability of the aurora occurring by comparing the forecasts with auroral boundaries determined from data from the IMAGE satellite between 2000 and 2002. Our analysis shows that the operational model performs well at predicting the location of the auroral oval, with a relative operating characteristic (ROC) score of 0.82. The model performance is reduced in the dayside local time sectors (ROC score = 0.59) and during periods of higher geomagnetic activity (ROC score of 0.55 for Kp = 8). As a probabilistic forecast, OVATION-Prime 2013 tends to underpredict the occurrence of aurora by a factor of 1.1–6, while probabilities of over 90% are overpredicted.

The open magnetic flux content of the magnetosphere varies during substorms as a result of dayside and nightside reconnection. The open flux can be calculated from the area of the polar cap, delineated by the open-closed field line boundary (OCB). This study presents a superposed epoch analysis of the location of the OCB and the change in the magnetic flux content in individual nightside MLT sectors during substorm growth, expansion, and recovery phases. Far ultraviolet (FUV) observations from the IMAGE satellite are used to derive a proxy of the OCB location. In the hour prior to substorm onset, the total nightside flux content increases by up to 0.12 GWb on average, resulting in an equatorward expansion of the OCB. Following substorm onset, the OCB contracts toward the pole as the open magnetic flux content decreases by up to 0.14 GWb on average, but the rate of decrease of the total nightside open flux content differs by 5–66% between the three IMAGE far ultraviolet instruments. The OCB does not contract poleward uniformly in all nightside magnetic local time (MLT) sectors after substorm onset. Close to the substorm onset MLT sector, the OCB contracts immediately following substorm onset; however, the OCB in more dawnward and duskward MLT sectors continues to expand equatorward for up to 120 minutes after substorm onset. Despite the continued increase in flux in these sectors after substorm onset, the total nightside flux content decreases immediately at substorm onset, indicating that the nightside reconnection rate exceeds the dayside rate following substorm onset.