Abstract
AbstractThis paper presents observations of polar cap arc substructure down to scale sizes of meters and temporal resolution of milliseconds. Two case studies containing polar cap arcs occurring over Svalbard are investigated. The first occurred on 4 February 2016 and is consistent with formation on closed field lines; the second occurred on 15 December 2015 and is consistent with formation on open field lines. These events were identified using global‐scale images from the Special Sensor Ultra‐violet Spectrographic Imager (SSUSI) instruments on board Defense Meteorological Satellite Program (DMSP) spacecraft. Intervals when the arcs passed through the small‐scale field of view of the Auroral Structure and Kinetics (ASK) instrument, located on Svalbard, were then found using all sky images from a camera also located on Svalbard. These observations give unprecedented insight into small‐scale polar cap arc structure. The energy and flux of the precipitating particles above these arcs are estimated using the ASK observations in conjunction with the Southampton Ionospheric model. These estimates are then compared to in situ DMSP particle measurements, as well as data from ground‐based instrumentation, to infer further information about their formation mechanisms. This paper finds that polar cap arcs formed on different magnetic field topologies exhibit different behavior at small‐scale sizes, consistent with their respective formation mechanisms.
Highlights
Polar cap arcs occur at high latitudes in the typically dim polar cap region
This paper finds that polar cap arcs formed on different magnetic field topologies exhibit different behavior at small‐scale sizes, consistent with their respective formation mechanisms
The arcs were classified as consistent with occurrence on different magnetic topologies in each event, based on the associated particle precipitation and if there were observed in Sensor Ultra‐violet Spectrographic Imager (SSUSI) images from one or both hemispheres
Summary
Polar cap arcs occur at high latitudes in the typically dim polar cap region. They are correlated with quiet magnetospheric conditions and northward Interplanetary Magnetic Field (IMF) (Berkey et al, 1976; Gussenhoven et al, 1984). Large‐scale polar cap arcs, such as the theta aurora discovered by Frank et al (1982), have been found to be associated with particle precipitation of the same energy and brightness as that seen over the auroral oval Such precipitation, including both ion and electron signatures, has been recorded by many authors when investigating polar cap aurora using high‐altitude spacecraft images, for example, Frank et al (1982) and Fear et al (2014). Carlson and Cowley (2005) suggest that weaker polar cap arcs viewed from the ground are distinct from the larger scale arcs viewed from space and are driven by a different formation mechanism They state that any modest mechanism which can drive shear flow across open field lines could accelerate polar rain to high enough energies to produce polar cap aurora on these open field lines.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
