Search

We analyze the properties of relativistic (>700 keV) electron precipitation (REP) events measured by the low-Earth-orbit (LEO) POES/MetOp constellation of spacecraft from 2012 through 2023. Leveraging the different profiles of REP observed at LEO, we associate each event with its possible driver: waves or field line curvature scattering (FLCS). While waves typically precipitate electrons in a localized radial region within the outer radiation belt, FLCS drives energy-dependent precipitation at the edge of the belt. Wave-driven REP is detected at any MLT sector and L shell, with FLCS-driven REP occurring only over the nightside–a region where field line stretching is frequent. Wave-driven REP is broader in radial extent on the dayside and accompanied by proton precipitation over 03–23 MLT, either isolated or without a clear energy-dependent pattern, possibly implying that electromagnetic ion cyclotron (EMIC) waves are the primary driver. Across midnight, both wave-driven and FLCS-driven REP occur poleward of the proton isotropic boundary. On average, waves precipitate a higher flux of >700 keV electrons than FLCS. Both contribute to energy deposition into the atmosphere, estimated of a few MW. REP is more associated with substorm activity than storms, with FLCS-driven REP and wave-driven REP at low L shells occurring most often during strong activity (SML* < −600 nT). A preliminary analysis of the Solar Wind (SW) properties before the observed REP indicates a more sustained (∼5 h) dayside reconnection for FLCS-driven REP than for wave-driven REP (∼3 h). The magnetosphere appears more compressed during wave-driven REP, while FLCS-driven REP is associated with a faster SW of lower density. These findings are useful not only to quantify the contribution of >700 keV precipitation to the atmosphere but also to shed light on the typical properties of wave-driven vs FLCS-driven precipitation which can be assimilated into physics-based and/or predictive radiation belt models. In addition, the dataset of ∼9,400 REP events is made available to the community to enable future work. [ABSTRACT FROM AUTHOR]

Whistler mode waves in the plasmasphere and plumes drive significant losses of energetic electrons from the Earth's radiation belts into the upper atmosphere. In this study, we conducted a survey of amplitude‐dependent whistler wave properties and analyzed their associated background plasma conditions and electron fluxes in the plasmasphere and plumes. Our findings indicate that extremely large amplitude (>400 pT) whistler waves (a) tend to occur at L > 4 over the midnight‐dawn‐noon sectors and have small wave normal angles; (b) are more likely to occur during active geomagnetic conditions associated with higher fluxes of anisotropic electrons at 10 s keV energies; and (c) tend to occur at higher latitudes up to 20° with increasing amplitude. These results suggest that extremely large amplitude whistler waves in the plasmasphere and plumes could be generated locally by injected electrons during substorms and further amplified when propagating to higher latitudes. Plain Language Summary: Whistler mode waves are known as one of the primary drivers of precipitating energetic electrons from the Earth's radiation belts into the upper atmosphere. We utilize plasma wave observations from the Van Allen Probes mission and conduct a survey of whistler mode waves inside the plasmasphere and plumes, which are plasma regions surrounding the Earth and filled with high‐density cold electrons. Statistical results indicate that extremely large amplitude whistler waves are more likely to occur at large L shells (L shell is defined as the distance from magnetic field lines to the center of the Earth at the magnetic equator) in the post‐midnight sectors during active geomagnetic conditions associated with high fluxes of tens of keV electrons exhibiting anisotropic pitch angle distributions (with a flux peak in the direction that is perpendicular to the background magnetic field). These waves tend to occur at higher latitudes with increasing amplitude. Results suggest that these waves could be generated locally by injected electrons during substorm activity and may be further amplified when propagating to higher latitudes. Key Points: Van Allen Probes wave measurements are used to statistically analyze the whistler waves in the plasmasphere or plume regionsExtremely large amplitude (>400 pT) whistler waves tend to occur at L shells >4 over 0–18 hr MLT with small wave normal angles (<10°)Larger amplitude whistler waves are observed during more active substorm activities and higher magnetic latitudes [ABSTRACT FROM AUTHOR]

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 this direct effect on NOx, ozone, and atmospheric dynamics 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. Data from both hemispheres (55-70° N/S) are combined in daily flux estimates. 164 peaks above the 90th percentile of the > 30 keV flux are identified. These peaks are categorized into absolute E1 and E3 events representing weak and strong > 300 keV responses, respectively. A subset of absolute E1 and E3 events with similar > 30 keV responses is termed overlapping events. Additionally, relative E1 and E3 events are determined by the relative strength of the > 300 keV response, scaled by the initial > 30 keV flux. A comparison between E1 and E3 events aims to identify solar wind and geomagnetic conditions leading to high-energy EEP responses and to gain insight into the conditions that generate a high-energy tail, independent of the initial > 30 keV flux level. Superposed epoch analysis of mesospheric NO density from SOFIE confirms an observable direct impact on lower mesospheric chemistry associated with the absolute E3 events. A probability assessment based on absolute events identifies specific thresholds in the solar wind- magnetosphere coupling function (epsilon) and the geomagnetic indices Kp*10 and Dst, capable of determining the occurrence or exclusion of absolute E1 and E3 events. Elevated solar wind speeds persisting in the recovery phase of a deep Dst trough appear characteristic of overlapping and relative E3 events. This study provides insight into which parameters are important for accurately modeling the high-energy tail of EEP. [ABSTRACT FROM AUTHOR]