Auroral activity and ion distribution associated with magnetotail earthward-propagating dipolarization fronts

Earthward-propagating dipolarization fronts (DFs) are often found to be associated with magnetotail reconnection and Bursty Bulk Flows (BBFs) in the tail. Recently the THEMIS observations show a DF propagating over 10RE from the mid-tail region to the near-Earth tail region and THEMIS All-Sky Imager data shows a north-south auroral form and intensification of westward auroral zone currents. In this study, we examine THEMIS in situ and ground-based NORSTAR Meridian Scanning Photometers (MSP) observations of DFs in the tail and simultaneously observed changes in the proton aurora. We find that Earthward-moving DFs are often associated with intensification of proton aurora when the THEMIS spacecraft are conjugate to the meridian of the MSP. The proton aurora intensifications are transient and in some cases detached from the background proton precipitation. It is also found that right before the DFs the ion distribution is anisotropic in the field-aligned direction (mostly Earthward) and the ion energy increases. These observations suggest that the plasma sheet protons can be reflected and energized by the Earthward-moving DFs as DFs propagate through the magnetotail. These energized protons are reflected back to the stretched magnetic field in front of DFs and can be scattered into the loss-cone to precipitate into the ionosphere. We postulate that this population of ions is the source of the intensification of proton aurora observed on the ground.