Electron Precipitation From the Outer Radiation Belt During the St. Patrick's Day Storm 2015: Observations, Modeling, and Validation

Abstract

Recently, a model for medium‐energy (30–1000 keV) radiation belt‐driven electron precipitation (ApEEP) has been put forward for use in decadal to century‐long climate model runs as part of the Climate Modelling Intercomparison Project, phase 6 (CMIP6). The ApEEP model is based on directly observed precipitation data spanning 2002–2012 from the constellation of low‐Earth‐orbiting Polar Operational Environmental Satellites (POES). Here, we test the ApEEP model's ability using its magnetic local time variant, ApEEP_MLT, to accurately represent electron precipitation fluxes from the radiation belts during a large geomagnetic storm that occurred outside of the span of the development data set. In a study of narrowband subionospheric very low frequency (VLF) transmitter data collected during March 2015, continuous phase observations have been analyzed throughout the entire St. Patrick's Day geomagnetic storm period for the first time. Using phase data from the U.K. transmitter, call‐sign GVT (22.1 kHz), received in Reykjavik, Iceland, electron precipitation fluxes from L = 2.8 to 5.4 are calculated around magnetic local noon (12 MLT) and magnetic midnight (00 MLT). VLF‐inferred >30‐keV fluxes are similar to the equivalent directly observed POES fluxes. The ApEEP_MLT >30‐keV fluxes for L < 5.5 describe the overall St. Patrick's Day geomagnetic storm‐driven flux enhancement well, although they are a factor of 1.7 (1.3) lower than POES (VLF‐inferred) fluxes during the recovery phase. Such close agreement in >30‐keV flux levels during a large geomagnetic storm, using three different techniques, indicates this flux forcing are appropriate for decadal climate simulations for which the ApEEP model was created.

HEPPA III Intercomparison Experiment on Electron Precipitation Impacts: 1. Estimated Ionization Rates During a Geomagnetic Active Period in April 2010

“…The MEE ionization rate data set therein is based on the POES MEPED observations, and it uses the geomagnetic Ap index as a proxy to provide an extended time series beyond the satellite observation period (van de Kamp et al, 2016). There is, however, an ongoing debate to what extent this approach gives a representative flux level (Clilverd et al, 2020;Mironova et al, 2019;Nesse Tyssøy et al, 2019;Pettit et al, 2019). The discrepancies between the different ionization rate estimates might to a large extent be attributed to the different choices made in dealing with the instrumental challenges.…”

The Predictive Capabilities of the Auroral Electrojet Index for Medium Energy Electron Precipitation

“…The MEE ionization rate dataset therein is based on observations from the Medium Energy Proton and Electron Detector (MEPED) instrument on board the NOAA/Polar Orbiting Environmental Satellites (POES), and the geomagnetic Ap index is used as a proxy to provide an extended time series beyond the satellite observation period (van de Kamp et al, 2016). There is, however, an active discussion to what extent this approach gives a representative flux and ionization rate level (Mironova et al, 2019;Nesse Tyssøy et al, 2019;Pettit et al, 2019;Clilverd et al, 2020). The CMIP6 flux is a general underestimate, largely ascribed to the use of the vertical (0°) detector on MEPED which only covers a small fraction of the loss cone (Nesse Tyssøy et al, 2019).…”

Impacts of UV Irradiance and Medium-Energy Electron Precipitation on the North Atlantic Oscillation during the 11-Year Solar Cycle

“…The ApEEP model was specifically designed for long-term climate runs spanning outside of time periods when satellite precipitation measurements exist. In their study validating the APEEP model forcing, [55] recommended using EEP from direct POES measurements during time periods when such observations exist, and as applied here through ISSI-19. To allow for easy use of the ISSI-19 ionization rates in atmosphere and climate simulations, they were prepared consistent with the ApEEP dataset.…”