The High-Energy Tail of Energetic Electron Precipitation: Solar Wind Drivers and Geomagnetic Responses

Compositional NOx changes caused by energetic electron precipitation (EEP) at a specific altitude and those co-dependent on vertical transport are referred to as the EEP direct and indirect effect, respectively. The direct effect of EEP at lower mesospheric and upper stratospheric altitudes is linked to the high-energy tail of EEP (>300 keV). The relative importance of the two effects on NOx and their subsequent impact on ozone and dynamical changes at these altitudes remains unresolved due to inadequate particle measurements and scarcity of polar mesospheric NOx observations. An accurate parameterization of the high-energy tail of EEP is, therefore, crucial. This study utilizes EEP flux data from MEPED aboard the POES/Metop satellites from 2004 - 2014 to distinguish >30 keV events from >300 keV events. Data from the Northern and Southern Hemispheres (55-70oN/S) are combined in daily flux estimates. Flux peaks above the 90th percentile of the >30 kev flux are identified. The 33% highest and lowest associated responses in the >300 keV fluxes are labeled "E3 events" and "E1 events", respectively, resulting in 55 events of each type. A sub-selection of "overlapping events" is created based on similar >30 keV fluxes responses. Superposed epoch analysis of mesospheric NO density from SOFIE confirms an observable direct impact on lower mesospheric chemistry associated with E3 events. Elevated solar wind speeds persisting in the recovery phase of a deep Dst trough are characteristic of E3 events. A probability assessment identifies specific thresholds in the solar wind-magnetosphere coupling function (epsilon) and the geomagnetic indices Kp*10 and Dst, crucial for determining the occurrence or exclusion of E1 and E3 events. This study provides insight into which parameters are important for accurately modeling the high-energy tail of EEP.