Auroral Power and Magnetic Wave Activity During Substorms

The broadband acceleration of auroral electrons has both been associated with ULF wave activity and shown statistically to increase in occurrence at substorm expansion phase onset. In this paper, we show that auroral and magnetic fluctuations immediately prior to auroral break-up are intimately related, possessing the same initiation time and location, and frequency content. We present specific case studies and statistics of the evolution of ground-based and in-situ magnetic wave power and ground-based auroral intensity throughout the late growth phase and expansion phase of the substorm cycle. We show strong evidence that some substorm-related auroral enhancements are clearly and demonstrably linked to the evolution of ULF wave power, whilst interestingly some auroral forms are not. We discuss the implications of these results with regards to the possible drivers of auroral acceleration in the magnetosphere.