Multi-instrument observations of ULF wave-driven discrete auroral arcs propagating sunward and equatorward from the poleward boundary of the duskside auroral oval

Abstract

An investigation into how discrete frequency fast mode waves propagating sunward from the magnetotail may drive field line resonant Alfvén waves on closed field lines on the afternoon flank of the Earth’s magnetosphere is presented. Due to the morphology of the magnetic field lines on the flank, higher latitude poleward boundary auroral field lines map deeper into the magnetotail, implying that phase lags from mode coupling to sunward propagating fast mode waves in this stretched field geometry can overcome the standard poleward phase propagation of typical field line resonances, producing resonant Alfvén wave-driven discrete auroral arcs that propagate equatorward on closed field lines. A comparison is made between the predicted results and magnetometer, all sky camera and meridian scanning photometer observations of multiple east–west aligned discrete auroral arcs that propagate equatorward and sunward from the poleward boundary of the dayside auroral oval between 1400 and 1500 UT (approximately 1600 to 1700 MLT) on 3 January 1998. From this comparison, the conclusion is reached that the observations are consistent with the theoretical picture of discrete auroral arcs being driven by Alfvénic waves on closed field lines, the Alfvén waves being excited by discrete frequency fast mode waves propagating sunward from the magnetotail in the flank waveguide of the outer magnetosphere.