Intercomparison of the POES/MEPED Loss Cone Electron Fluxes With the CMIP6 Parametrization

Abstract

Quantitative measurements of medium energy electron (MEE) precipitation (>40 keV) are a key to understand the total effect of particle precipitation on the atmosphere. The Medium Energy Proton and Electron Detector (MEPED) instrument on board the NOAA/Polar Orbiting Environmental Satellites (POES) has two sets of electron telescopes pointing ~0° and ~90° to the local vertical. Pitch angle anisotropy, which varies with particle energy, location, and geomagnetic activity, makes the 0° detector measurements a lower estimate of the flux of precipitating electrons. In the solar forcing recommended for Coupled Model Intercomparison Project (CMIP) 6 (v3.2) MEE precipitation is parameterized by Ap based on 0° detector measurements hence providing a general underestimate of the flux level. In order to assess the accuracy of the Ap model, we compare the modeled electron fluxes with estimates of the loss cone fluxes using both detectors in combination with electron pitch angle distributions from theory of wave‐particle interactions. The Ap model falls short in respect to reproducing the flux level and variability associated with strong geomagnetic storms (Ap > 40) as well as the duration of corotating interaction region storms causing a systematic bias within a solar cycle. As the Ap‐parameterized fluxes reach a plateau for Ap > 40, the model's ability to reflect the flux level of previous solar cycles associated with generally higher Ap values is questioned. The objective of this comparison is to understand the potential uncertainty in the energetic particle precipitation applying the CMIP6 particle energy input in order to assess its subsequent impact on the atmosphere.

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

“…The analysis presented here provides a detailed comparison between satellite >30-keV electron precipitation flux measurements, VLF phase-inferred fluxes, and the CMIP6 predictive flux model during one large geomagnetic storm. The finding that the CMIP6 model of predicted electron precipitation (ApEEP) underrepresents geomagnetic storm-time fluxes is consistent with previous analysis undertaken by Nesse Tyssøy et al (2019), although the underestimate is found to be small. Realistic electron precipitation fluxes, as inferred from VLF signal analysis and POES observations during the storm, could be as large as a factor of 1.7 higher than currently estimated by the ApEEP predictive model (Matthes et al, 2017).…”

“…In our study, the MLT version of the ApEEP model is required in order to compare against the specific VLF propagation path analyzed. However, van de Kamp et al (2018) showed that the ApEEP_MLT model-predicted fluxes, when zonally averaged, generated fluxes equivalent to that of the non-MLT model used in CMIP6, so we can assume the conclusions of Nesse Tyssøy et al (2019) to also be valid for the ApEEP_MLT modelpredicted fluxes. Figure 9 shows 24-hr average >30-keV electron precipitation fluxes determined using the ApEEP_MLT model, VLF phase perturbations, and the longitudinally restricted POES >30-keV measurements.…”

“…Nesse Tyssøy et al (2019) concluded that the CMIP6 >30-keV fluxes are potentially underrepresented during geomagnetic storms with large Ap and provide a general underestimate because of the limitations of the POES electron precipitation telescope (Nesse Tyssøy et al, 2016). We note that the ApEEP model-predicted fluxes used in CMIP6 analysis does not include any MLT variability, while the ApEEP_MLT does.…”

“…Nesse Tyssøy et al (2019) concluded that the ApEEP model >30-keV fluxes are potentially too low during geomagnetic storms with Ap > 40 nT, partly because of pitch angle anisotropy within the bounce loss cone (BLC). However, Rodger et al (2013) used satellite electron precipitation observations combined with ground-based riometer absorption to show that the BLC was isotropic during high flux EEP events, that is, indicating strong diffusion.…”

Outer Van Allen belt trapped and precipitating electron flux responses to two interplanetary magnetic clouds of opposite polarity

“…Both telescopes have a 30 • angle of view and records electron flux in three energy channels: > 30 keV, > 100 keV, and > 300 keV. Unfortunately, the use of POES for electron precipitation measurements have several significant problems, such 150 as proton contamination and varying detector efficiency that are both well-documented in the literature (e.g., Asikainen and Mursula, 2013;Rodger et al, 2010b;Tyssoy et al, 2019). The POES data used here has been corrected for these instrumental problems (Asikainen and Mursula, 2011;Asikainen et al, 2012;Asikainen and Mursula, 2013).…”