Energetics and Alfvenic Coupling of a Poleward Boundary Intensification: A Polar Case Study

摘要

The poleward boundary intensification (PBI) is a common appearance at the poleward boundary of the auroral bulge and auroral oval. The PBI presented here occurred during the expansion phase of a small substorm with an auroral surge power of 6.5 GW. The auroral power of the PBI (1.1 GW) was similar to 17 of this value. The largest powers above the nominal auroral acceleration region at 5 R-E geocentric were carried by Alfven waves (1.7 GW) and Alfvenic electrons (0.7 GW), sufficient to account for the conjugate PBI auroral power. In contrast, the conjugate quasistatic, field-aligned current power (<0.3 GW) was not sufficient. Observed correlation between quasiperiodic Alfvenic pulses and auroral modulations strengthens our conclusion that the electromagnetic magnetosphere-ionosphere coupling of the PBI was dominantly Alfvenic, as opposed to electrostatic, thus causing Alfvenic aurora.