Local geomagnetic indices and the prediction of auroral power

摘要

The aurora has been related to magnetometer observations for centuries and to geomagnetic indices for decades. As the number of stations and data processing power increases, just how auroral power (AP) relates to geomagnetic observations becomes a more tractable question. This paper compares Polar ultraviolet imager AP observations during 1997 with a variety of indices. Local time (LT) versions of the SuperMAG auroral electrojet (SME) are introduced and examined, along with the corresponding upper and lower envelopes (SMU and SML). Also, the east-west component, B_E, is investigated. We also consider whether using any of the local indices is actually better at predicting local AP than a single global index. Each index is separated into 24 LT indices with a sliding 3 hmagnetic local time (MLT) window. The ability to predict AP varies greatly with LT, peaking at 19:00 MLT, where about 75% of the variance (r~2) is predicted at 1min cadence. The aurora is fairly predictable from 17:00 MLT to 04:00 MLT, roughly the region in which substorms occur. AP is poorly predicted from auroral electrojet indices from 05:00 MLT to 15:00 MLT, with theminimum at 10:00–13:00 MLT. In the region of high predictability, the local index which works best is B_E (east-west), in contrast to long-standing expectations. However, using global SME is better than any local index. AP is best predicted by combining global SME with a local index: B_E from 15:00 to 03:00 MLT and either SMU or SML from 03:00 to 15:00 MLT. In the region of the diffuse aurora, it is better to use a 30min average than the cotemporaneous 1min SME value, while from 15:00 to 02:00 MLT, the cotemporaneous 1 min SME works best, suggesting a more direct physical relationship with the auroral circuit. These results suggest a significant role for discrete auroral currents closing locally with Pedersen currents.