Nightside Auroral H+ and O+ Outflows versus Energy Input During a Geomagnetic Storm

Recalibrated FAST/Time-of-Flight Energy, Angle, and Mass Spectrograph (TEAMS) data is used to investigate the correlations between the H⁺ and O⁺ outflows from the nightside auroral oval zone and the parameters related to energy input to the Earth's ionosphere. The data is collected during the 24 - 25 September 1998 geomagnetic storm following a coronal mass ejection (CME) event. Those parameters include the Alfvénic Poynting flux (S_ac) associated with waves at frequencies from 0.125 to 0.5 Hz, the quasistatic Poynting flux (S_dc) measuring the fluctuations with frequencies below 0.125 Hz, the omni-directional number flux of electrons (f_en), the omni-directional energy flux of the electrons (f_ee), the density of electrons in the loss cone (n_ep, given by Strangeway et al., 2005, doi:10.1029/2004JA010829), and the amplitude of the extreme low frequency (ELF) waves at frequencies from 30 Hz to 20 kHz (A_ELF). The Poynting flux is calculated as E_V×δB_west/μ₀, thus indicates the input electromagnetic energy to the ionosphere. This study is a follow-on to the studies of Strangeway et al., 2005 and Zhao et al. 2020 (doi:10.1029/2020GL086975), which examined the correlations between energy input and outflows in the cusp region for the same storm. On the nightside, energetic precipitating electrons and strong plasma convection are usually seen. In this study, (1) Empirical models of the outflow flux as a function of the parameters are constructed. (2) The H⁺/O⁺ outflow ratio is calculated to study its response to the energy input. (3) In addition, relationships between the strength of the convection and the energy input are also evaluated. Empirical models on the nightside are of interest and important for simulating ions of ionospheric origin being transported directly to the plasma sheet.