Modeling Stable Auroral Red (SAR) Arcs at Geomagnetic Conjugate Points: Implications for Hemispheric Asymmetries in Heat Fluxes

摘要

Stable auroral red (SAR) arcs provide opportunities to study inner magnetosphere-ionosphere coupling at midlatitudes. An imaging system at a single-site obtains evidence of seasonal variations in SAR arc brightness and occurrence rates using events widely separated in time, as observed during different geomagnetic storms. The first SAR arc observed using two all-sky imagers at geomagnetic conjugate points described seasonal effects at the same time for the same storm (Martinis, Mendillo, et al., 2019, https://doi. org/10.1029/2018JA026018). Here we report on modeling studies that enable specification of the roles of local "receptor conditions" in each hemisphere, plus the division of driving energy from a single source region into conjugate ionospheres. The geomagnetic storm of 1 June 2013 produced SAR arcs observed by conjugate all-sky imagers yielding 73 Rayleighs (R) at Millstone Hill (L = 2.64) in the summer hemisphere,and 300 R during local winter at Rothera (L = 2.92). With incoherent scatter radar data not available to specify input conditions, we offer a new simulation approach using non-incoherent scatter radar observations to specify local receptor conditions. These include a combination of semiempirical models (International Reference Ionosphere and MSIS) calibrated by local ionosonde and DMSP satellite data. We find that the driving mechanism (heat conduction entering the ionosphere) is not an equal partition of energy from the ring current source region, but one that is weaker in the summer hemisphere where the local receptor conditions are poised to produce fainter SAR arcs. The relationship between SAR arcs and recently discovered STEVE events are discussed and require further study.