Nightside Auroral H+ and O+ Outflows Versus Energy Inputs During a Geomagnetic Storm.

The recalibrated FAST/TEAMS data is used to study the response of O+ and H+ outflow to energy inputs in the nightside aurora during the 24–25 September 1998 geomagnetic storm, the same storm studied by Strangeway et al. (2005), https://doi.org/10.1029/2004JA010829. In contrast to the cusp, the Poynting flux and electron precipitation energy input are not as well correlated on the nightside, so their effects on outflow can be differentiated. The O+ outflow shows a strong correlation with both the Alfvénic Poynting flux (r = 0.71) and the soft electron precipitation (r = 0.69), while the H+ outflow only correlates well with the electron number flux (r = 0.74). This indicates that the auroral H+ outflow is close to its limiting flux without additional wave acceleration, while the outflow for the heavier O+ ion is increased by additional wave acceleration. Plain Language Summary: Geomagnetic activity can cause electrons to precipitate into the ionosphere in the nightside auroral region. It can also deliver electromagnetic wave energy to the same region. The electron precipitation can both heat and further ionize the ionosphere, leading to ions moving up along the field line. The wave energy can further accelerate the ions. If the ions are accelerated enough by these processes, they will flow out along the magnetic field, escaping the ionosphere. This paper finds that the H+ outflow increases with increased precipitating electrons in the nightside aurora. The O+ outflow increases with both electron precipitation and wave acceleration. Key Points: Electron precipitation and Poynting flux are less correlated on the nightside than the cusp, so their effects on outflow can be distinguishedO+ outflow is correlated with both Poynting flux and electron precipitation, while H+ is only correlated with electron precipitationParameterization of the outflow dependence is consistent between the dayside cusp and the nightside auroral regions [ABSTRACT FROM AUTHOR]