... The midlatitude stable red auroral red (SAR) arcs are well known examples of electron heating in the upper F - region (400 km) of the Earth's ionosphere that produces red aurora (see low-latitude aurorae ). ... The ultimate energy source of SAR arcs can be found in the magnetospheric ring current region. ... Since SAR arcs occur in the low-density trough region, this energy input is distributed among fewer electrons than in the surrounding area and can result in highly elevated electron temperatures...