SubAuroral Red Arcs Generated by Inner Magnetospheric Heat Flux and by SubAuroral Polarization Streams

Subauroral red (SAR) arcs are commonly observed ionospheric red line emissions. They are usually attributed to subauroral electron heating by inner magnetospheric heat flux (IMHF). However, the role of IMHF in changing the ionosphere‐thermosphere (IT) still remains elusive. We conduct controlled numerical experiments with the Thermosphere‐Ionosphere Electrodynamic General Circulation Model (TIEGCM). Coulomb collisional heat flux derived with the Comprehensive Inner Magnetosphere Ionosphere (CIMI) model and empirical subauroral polarization streams (SAPS) are implemented in TIEGCM. The heat flux causes electron temperature enhancement, electron density depletion, and consequently SAR arcs formed in the dusk‐to‐midnight subauroral ionosphere region. SAPS cause more substantial plasma and neutral heating and plasma density variations in a broader region. The maximum enhancement of subauroral red line emission rate is comparable to that caused by the heat flux. However, the visibility of SAR arcs also depends on the relative enhancement to the background brightness. The Earth's topside atmosphere is subject to energy inputs from the magnetosphere and solar wind. In addition to the Joule heating generated by high latitude plasma convection and energy flux carried by precipitating magnetospheric particles, magnetospheric energy can be also deposited in the ionosphere‐thermosphere via heat flux, that is, energy flows carried by low‐energy thermal electrons. When hot ions in the ring current collide with the cold plasma in the plasmasphere, heat conduction occurs and the resultant heat flux is transported along geomagnetic field lines to the footprint ionosphere. The additional heating raises the electron temperature in the subauroral ionosphere and modifies the ionosphere‐thermosphere states. This study uses first‐principles inner magnetosphere model and ionosphere‐thermosphere model to illustrate the thermodynamic coupling effects between the topside ionosphere and the magnetosphere, and compare the relative significance between the heat flux and plasma convection due to electrodynamic coupling. The numerical experiments show that the heat flux primarily increases electron temperature while subauroral plasma flow heats up both plasma and neutrals. Despite different physical mechanisms, the heat flux and subauroral plasma convection make comparable contributions to red line emission rates in the subauroral region. Inner magnetospheric heat flux increases subauroral ionospheric electron temperature and depletes the density to form subauroral red arcsCompared to subauroral polarization streams, the heat flux heating effects are only confined to electrons in the subauroral regionThe heat flux produces negligible impacts on ions and neutrals compared to subauroral polarization streams Inner magnetospheric heat flux increases subauroral ionospheric electron temperature and depletes the density to form subauroral red arcs Compared to subauroral polarization streams, the heat flux heating effects are only confined to electrons in the subauroral region The heat flux produces negligible impacts on ions and neutrals compared to subauroral polarization streams