Reliability of Matching AMPERE Field-Aligned Current Boundaries with
SuperDARN Lower Latitude Ionospheric Convection Boundaries During
Geomagnetic Storms
Abstract
High-latitude ionospheric convection is a useful diagnostic of solar
wind-magnetosphere interactions and nightside activity in the
magnetotail. For decades, the high-latitude convection pattern has been
mapped using the Super Dual Auroral Radar Network (SuperDARN), a
distribution of ground-based radars which are capable of measuring
line-of-sight (l-o-s) ionospheric flows. From the l-o-s measurements an
estimate of the global convection can be obtained. As the SuperDARN
coverage is not truly global, it is necessary to constrain the maps when
the map fitting is performed. The lower latitude boundary of the
convection, known as the Heppner-Maynard boundary (HMB), provides one
such constraint. In the standard SuperDARN fitting, the HMB location is
determined directly from the data, but data gaps can make this
challenging. In this study we evaluate if the HMB placement can be
improved using data from the Active Magnetosphere and Planetary
Electrodynamics Response Experiment (AMPERE), in particular for active
time periods when the HMB moves to latitudes below 55°. We find that the
boundary as defined by SuperDARN and AMPERE are not always co-located.
SuperDARN performs better when the AMPERE currents are very weak (e.g.
during non-active times) and AMPERE can provide a boundary when there is
no SuperDARN scatter. Using three geomagnetic storm events, we show that
there is agreement between the SuperDARN and AMPERE boundaries but the
SuperDARN-derived convection boundary mostly lies ~3°
equatorward of the AMPERE-derived boundary. We find that disagreements
primarily arise due to geometrical factors and a time lag in expansions
and contractions of the patterns.