Substorm‐induced energetic electron precipitation: Morphology and prediction

Abstract

Key Points:• Model substorm precipitation is validated with ground-based observations • All four types of riometer spike event emerge in the model results • Model can predict precipitation hours after a substorm onset is detected AbstractThe injection, and subsequent precipitation, of 20 to 300 keV electrons during substorms is modeled using parameters of a typical substorm found in the literature. When combined with onset timing from, for example, the SuperMAG substorm database, or the Minimal Substorm Model, it may be used to calculate substorm contributions to energetic electron precipitation in atmospheric chemistry and climate models. Here the results are compared to ground-based data from the Imaging Riometer for Ionospheric Studies riometer in Kilpisjärvi, Finland, and the narrowband subionospheric VLF receiver at Sodankylä, Finland. Qualitatively, the model reproduces the observations well when only onset timing from the SuperMAG network of magnetometers is used as an input and is capable of reproducing all four categories of substorm associated riometer spike events. The results suggest that the different types of spike event are the same phenomena observed at different locations, with each type emerging from the model results at a different local time, relative to the center of the injection region. The model's ability to reproduce the morphology of spike events more accurately than previous models is attributed to the injection of energetic electrons being concentrated specifically in the regions undergoing dipolarization, instead of uniformly across a single-injection region.

Utilizing the Heliophysics/Geospace System Observatory to Understand Particle Injections: Their Scale Sizes and Propagation Directions

“…Precipitating energetic electrons (~≥30 keV) can reach the D region of the atmosphere where collision frequencies are high enough to affect ionization rates and attenuate high‐frequency radio waves as they pass through the ionosphere. Previous studies have shown that if flux conditions for strong pitch angle scattering are met, meaning, that the Kennel‐Petschek limit is exceeded (Kennel & Petschek, ), integrated electron flux >30 keV is correlated with riometer absorption observed at the spacecraft's magnetic foot point (Baker et al, ; Beharrell et al, ; Clilverd et al, ; Kellerman et al, ; Spanswick et al, ). Spanswick et al () determined that if the riometer absorption ramps up and peaks within 3 min, the signature is correlated with a dispersionless injection in space.…”

Self‐Consistent Modeling of Electron Precipitation and Responses in the Ionosphere: Application to Low‐Altitude Energization During Substorms

“…Transient structures in the ionosphere, including sudden enhancement of ionization in the low-altitude D region (e.g., Cresswell-Moorcock et al, 2013;Rodger et al, 2012), have important implications to terrestrial atmosphere dynamics, including ozone loss (e.g., Seppälä et al, 2015). The low-altitude structures can be attributed to solar proton events between 1 and 100 MeV in energy (e.g., Clilverd et al, 2005;Reagan & Watt, 1976) or energetic electron precipitation from the magnetosphere (e.g., Beharrell et al, 2015;McGranaghan, Knipp, Matsuo, et al, 2015;Oyama et al, 2017;Sivadas et al, 2017). There have been extensive reports that the Geophysical Research Letters 10.1029/2018GL078828 energetic electrons in the ring current/radiation belts and plasma sheet can precipitate into the ionosphere through various mechanisms (e.g., Fu et al, 2011;Horne et al, 2003;Jordanova et al, 2008;Li et al, 2017Li et al, , 2013Newell et al, 2009;Ni et al, 2008;Su et al, 2017;Thorne et al, 2010).…”

Substorm‐induced energetic electron precipitation: Impact on atmospheric chemistry

“…Magnetospheric substorms are short‐lived reconfigurations of the geomagnetic field and result in energetic electron precipitation (EEP) into the atmosphere lasting several hours [ Akasofu , ; Cresswell‐Moorcock et al , ]. Electron precipitation energies during substorms can occur from 20 keV to 1 MeV, although typically the range is 20–300 keV [ Beharrell et al , ]. During the substorm injection process, electron precipitation is initially detected at L ∼6 [ Cresswell‐Moorcock et al , ] and expands equatorward and poleward with time.…”