Morphology and Dynamics of Auroral Arc

Abstract:

A magnetic substorm is the result of an explosive release of energy on the night-side magnetosphere due to the coupling of the solar wind and interplanetary magnetic field (IMF) with the Earth’s magnetic field resulting in a storage of energy in the night side magnetosphere. The consequential auroral substorm is characterized by a rapid brightening and poleward expansion of the aurora following the release of energy in the night-side magnetosphere. Two predominant hypotheses exist which predict the sequence of events leading to substorm onset and the physical mechanism responsible for triggering this onset, the near-Earth neutral line (NENL) and current disruption models (CD). The NENL model suggest that onset is the result of magnetic reconnection between 10-20 Earth radii in the magnetotail. The CD model suggests onset is the result plasma instabilities forming inside of 10 Earth radii. This study examines a newer model presented by Nishimura et al. (2010, JGR), which suggests that enhanced earthward plasma flows from the distant magnetotail to the near-Earth region lead to sub-storm onset, which is manifested in the aurora by a poleward boundary intensification (PBI) and equatorward motion of a North-South auroral feature. The purpose of this study is to determine and identify the poleward-most and equatorward-most arcs, as well as the morphology of the aurora in order to develop a more complete picture of the auroral substorm and ultimately test the three substorm models described above. Preliminary results demonstrate that equatorward motion of the onset arc during the growth phase is typical and that no distinct North-South arcs exist during the growth phase. Future research will include characterizing the intensity and tracking the brightness of the arcs comparatively as well as the motion within the arc.