The Association of High‐Latitude Dayside Aurora With NBZ Field‐Aligned Currents. Issue 5 (11th May 2018)

• Record Type: Journal Article
• Authors: Carter, J. A.; Milan, S. E.; Fogg, A. R.; Paxton, L. J.; Anderson, B. J.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 5(2018)
• Page Start: 3637
• Page End: 3645
• Publication Date: 2018-05-11
• Subjects: aurora -- field‐aligned current -- ionosphere -- high‐latitude auroral emissions; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2017JA025082
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: The relationship between auroral emissions in the polar ionosphere and the large‐scale flow of current within the Earth's magnetosphere has yet to be comprehensively established. Under northward interplanetary magnetic field (IMF) conditions, magnetic reconnection occurs at the high‐latitude magnetopause, exciting two reverse lobe convection cells in the dayside polar ionosphere and allowing ingress of solar wind plasma to form an auroral "cusp spot" by direct impact on the atmosphere. It has been hypothesized that a second class of NBZ auroras, High‐latitude Dayside Aurora, are produced by upward field‐aligned currents associated with lobe convection. Here we present data from the Special Sensor Ultraviolet Spectrographic Imager instrument and from the Active Magnetosphere and Planetary Electrodynamics Response Experiment, from January 2010 to September 2013, in a large statistical study. We reveal a northward IMF auroral phenomenon that is located adjacent to the cusp spot and that is colocated with a region of upward electrical current in the clockwise‐rotating lobe cell. The emission only occurs in the sunlit summer hemisphere, demonstrating the influence of the conductance of the ionosphere on current closure. In addition, fast solar wind speed is required for this emission to be bright. The results show that dayside auroral emission is produced by IMF‐magnetosphere electrodynamic coupling, as well as by direct impact of the atmosphere by the solar wind, confirming the association of High‐latitude Dayside Aurora with NBZ currents. Plain Language Summary: Under certain incoming solar wind conditions, patches of aurora are sometimes found not in the main bright auroral oval but inside the normally otherwise dark polar cap region. These patches of auroral emissions are colocated with regions of upward flowing electrical current. We present a study of these emissions using nearly 3 years of data from both the North and South Hemispheres, combining simultaneous observations of the polar cap at ultraviolet wavelengths, and measurements of field‐aligned currents. This builds on the previous work of other authors, who observed these auroral emissions in the Northern Hemisphere only. The upward current associated auroral emissions occur when the incoming interplanetary magnetic field is northward and are shown to only be observable in the summer hemisphere. This implies a dependence on the conductance of the ionosphere, via photoionization, on the appearance of these auroras. Key Points: High‐latitude aurora and distributions of field‐aligned current from both hemispheres are compared under northward IMF conditions These high‐latitude auroras are co‐located with upward NBZ field‐aligned current The auroral emissions are only observed in the summer hemisphere, confirming a hypothesis of Frey (2007)