Identifying the evolution of Southern Hemisphere poleward moving auroral forms (PMAFs) in the context of plasma convection and magnetic reconnection

Abstract

In this study we examine the dynamic evolution of Southern Hemisphere auroral precipitation patterns, specifically poleward moving auroral forms (PMAFs). The spatial, structural, and temporal characteristics of these events have been linked to underlying magnetopause-boundary layer flux transfer events which are responsible for the generation of these ionospheric transient forms. We present five case studies of Southern Hemisphere PMAFs using optical data for 630.0 nm and 427.8 nm wavelengths from the US Automatic Geophysical Observatory Network in Antarctica. Emphasis is put on the unique capabilities of two-dimensional optical data when it comes to studying PMAFs in the context of pulsed magnetic reconnection. In a detailed examination of three PMAFs recorded in 2007, we have found that their motion closely follows the underlying plasma convection patterns as determined from backscatter radar data, which in turn are governed by the interplanetary magnetic field (IMF) configuration. Of particular interest are periods when the positive IMF By component causes an asymmetric convection pattern which is biased toward the dawn region. These cases are consistent with the expected antisymmetric nature of the northern and southern hemisphere convection. In addition, we present two “pseudo” PMAFs which are actually independent auroral arcs executing poleward motions and occurring when the IMF Bz was positive. Using two-dimensional images instead of one-dimensional keograms or meridian scanning photometer recordings, we were able to distinguish these arcs from PMAFs. The misidentification of these arcs as PMAFs would cause inconsistencies with the theories of cusp aurora dynamics and magnetic reconnection, and some previous studies may have included such non-PMAF events.