Two mechanisms for dayside polar cap auroral emissions under northward IMF

A localised region of auroral emissions in the dayside region of thehigh-latitude polar cap, known as a cusp spot, has been traditionallyassociated with northward interplanetary magnetic field (IMF)conditions. We compare contemporaneous auroral emissions with fieldaligned current configurations under a variety of IMF magnitudes andorientations. We observe dayside polar cap emissions in the LymanBirge Hopfield band, associated with upward field aligned currentsunder northward IMF, and at all IMF magnitudes. These emissions arenot associated with the standard cusp spot. The local time location ofthis emission is dependent on the By component of the IMF. We proposethat two mechanisms act to produce aurora emissions within the polarcap. The first results in the traditional cusp spot through directmagnetosheath precipitation on open field lines, which is general observedthrough Lyman-alpha emissions. The second is associated with region 0upward field aligned currents that arise from tension forces on newlyreconnected field lines in the magnetosphere lobes. We compare ourstatistical study with individual cases of cusp spot emission. Weinvestigate the control of the solar wind on each type of polar capemission and show that both the solar wind density and speed play asignificant role in the detection of these emissions.