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arxiv: 1906.10460 · v1 · pith:TLGZX4OPnew · submitted 2019-06-25 · ⚛️ physics.space-ph

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

H. Nesse Tyss{\o}y , A. Haderlein , M. I. Sandanger , J. Stadsnes This is my paper

Pith reviewed 2026-05-25 16:03 UTC · model grok-4.3

classification ⚛️ physics.space-ph
keywords medium energy electron precipitationPOES MEPEDCMIP6Ap indexgeomagnetic stormsloss cone fluxcorotating interaction regions
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The pith

The Ap parametrization in CMIP6 underestimates medium energy electron precipitation fluxes during strong geomagnetic storms.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper compares loss-cone estimates of medium energy electron precipitation derived from POES/MEPED satellite detectors against the Ap-based model adopted for CMIP6 solar forcing. The Ap model relies on the 0° detector alone and therefore under-samples the full precipitating flux because of varying pitch-angle distributions. When the two detectors are combined with theoretical pitch-angle distributions, the resulting loss-cone fluxes exceed the Ap model values, especially during strong storms with Ap greater than 40 and throughout the longer duration of corotating interaction region storms. A reader would care because these electrons deposit energy in the atmosphere and the CMIP6 inputs are used in climate and chemistry models.

Core claim

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.

What carries the argument

Loss-cone flux estimates obtained by combining the 0° and 90° MEPED electron detectors with electron pitch-angle distributions taken from wave-particle interaction theory.

If this is right

  • The CMIP6 particle energy input carries a systematic underestimate during strong storms.
  • Atmospheric models driven by the Ap parametrization will understate energy deposition and chemical effects from medium energy electrons.
  • A solar-cycle bias arises because the model does not capture the full length of corotating interaction region storms.
  • The plateau at Ap > 40 limits the parametrization's usefulness for earlier solar cycles that experienced higher Ap values.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Revised parametrizations for particle precipitation in climate models could be tested against loss-cone estimates from combined-detector data.
  • The identified shortfall may affect calculations of NOx production and ozone response that rely on CMIP6 solar forcing.

Load-bearing premise

Electron pitch angle distributions from wave-particle interaction theory, when combined with the two MEPED detectors, give an accurate estimate of the true loss-cone precipitating flux.

What would settle it

Independent measurements of precipitating electron fluxes during an Ap > 40 geomagnetic storm that match the lower levels given by the Ap model rather than the higher loss-cone estimates.

Figures

Figures reproduced from arXiv: 1906.10460 by A. Haderlein, H. Nesse Tyss{\o}y, J. Stadsnes, M. I. Sandanger.

Figure 1
Figure 1. Figure 1: (left column) The Ap‐modeled integral fluxes >43 keV (top) and >114 keV (bottom) as function of L shell and Ap. (right column) The median of the Medium Energy Proton and Electron Detector loss cone integral fluxes >43 keV (top) and >114 keV (bottom) based on all data from all magnetic local time sec￾tors of the years 2003–2012 as function L shell and Ap. Journal of Geophysical Research: Space Physics 10.10… view at source ↗
Figure 2
Figure 2. Figure 2: The median of the Medium Energy Proton and Electron Detector loss cone integral fluxes >43 keV (right) and >114 keV (left) based on all data from all magnetic local time sectors as function of L shell and Ap separately for the years (a. b) 2003, (c, d) 2005, and (e, f) 2008. Journal of Geophysical Research: Space Physics 10.1029/2018JA025745 TYSSØY ET AL. 633 [PITH_FULL_IMAGE:figures/full_fig_p006_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Integral fluxes >43 keV based on the Ap model and MEPED LC fluxes in years (a) 2003, (b) 2005, and (c) 2008 for three different L shell values, 4.25, 5.25, and 7.75. The MEPED LC fluxes are calculated using median treating data below the noise floor to a not a number and by calculating mean values treating data below the noise floor as zero value. The daily Ap index is shown in the lower panels. MEPED = Me… view at source ↗
Figure 4
Figure 4. Figure 4: for a typical CIR storm in 2008. The peak Ap value does not exceed 27 and the modeled Ap fluxes nicely follow the rise in Ap on DOY 114. Differences in peak flux levels between the Ap model and MEPED LC measurements persist but are expected due to the likely underestimation of LC fluxes by the 0° detector. This discrepancy, is, how￾ever, increased during the recovery phase of the storm. Bound to the Ap ind… view at source ↗
Figure 1
Figure 1. Figure 1: For example, for high Ap values >40 the flux levels are not sys￾tematically different for L shells between 4 and 8. The flux levels do not reach a plateau but increase about an order of magnitude between Ap values 30 and 80. (For Ap > 80 the statistics is poor, and it is hard to eval￾uate the Ap dependence.) Figure 5b shows how the modeled >114‐keV flux depends on the Ap index for different L values. At L … view at source ↗
Figure 5
Figure 5. Figure 5: Illustration of the Ap sensitivity of the flux levels themselves for (a) the >43‐keV fluxes and (b) the >114‐keV fluxes. Journal of Geophysical Research: Space Physics 10.1029/2018JA025745 TYSSØY ET AL. 637 [PITH_FULL_IMAGE:figures/full_fig_p010_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Number of days during each year with a daily Ap index >40 from 1970 to 2016. The black dotted line indicates the solar cycle given by the F10.7 radio flux and the grey area marks years considered in the Ap model derivation. Journal of Geophysical Research: Space Physics 10.1029/2018JA025745 TYSSØY ET AL. 638 [PITH_FULL_IMAGE:figures/full_fig_p011_6.png] view at source ↗
read the original 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 $\sim$0$^{\circ}$ and $\sim$90$^{\circ}$ to the local vertical. Pitch angle anisotropy, which varies with particle energy, location, and geomagnetic activity, makes the 0$^{\circ}$ 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$^{\circ}$ 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.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 1 minor

Summary. The manuscript intercompares loss-cone medium-energy electron fluxes reconstructed from POES/MEPED 0° and 90° telescope counts using theoretical pitch-angle distributions against the Ap-based parametrization adopted for CMIP6 (v3.2). It concludes that the Ap model underestimates both the flux level and variability for Ap > 40 and introduces a systematic bias in the duration of corotating interaction region (CIR) storms, with implications for atmospheric forcing over a solar cycle.

Significance. If the reconstructed fluxes are shown to be robust, the result would identify a concrete limitation in the CMIP6 solar-particle forcing that affects atmospheric chemistry and dynamics simulations during strong geomagnetic activity. The work performs an external comparison against independent satellite measurements rather than deriving results by internal fitting, which is a methodological strength.

major comments (2)
  1. [Methods] Methods section (loss-cone flux estimation): the reconstruction combines the two MEPED detectors with pitch-angle distributions taken from quasi-linear theory of chorus/EMIC scattering, yet no cross-validation against independent datasets (FIREBIRD, BARREL, or Van Allen Probes) or test-particle simulations is reported for the Ap > 40 or slot-region events. Because the central claim attributes all reported discrepancies to the Ap parametrization, this unverified assumption is load-bearing.
  2. [Results] Results (Ap > 40 regime): the claim that the Ap model reaches a plateau and therefore underestimates fluxes during strong storms rests on the accuracy of the theoretical-PAD reconstruction; without demonstrated robustness of that reconstruction under the same conditions, the reported bias cannot be unambiguously assigned to the CMIP6 parametrization.
minor comments (1)
  1. [Abstract] Abstract: the statement that the Ap model 'falls short in respect to reproducing the flux level and variability' would be strengthened by an explicit reference to the figure or table that quantifies the underestimation factor.

Simulated Author's Rebuttal

2 responses · 1 unresolved

We thank the referee for the constructive comments on the validation of the loss-cone flux reconstruction. The points raised are well taken and we address them point-by-point below, indicating planned revisions to the manuscript.

read point-by-point responses

  1. Referee: [Methods] Methods section (loss-cone flux estimation): the reconstruction combines the two MEPED detectors with pitch-angle distributions taken from quasi-linear theory of chorus/EMIC scattering, yet no cross-validation against independent datasets (FIREBIRD, BARREL, or Van Allen Probes) or test-particle simulations is reported for the Ap > 40 or slot-region events. Because the central claim attributes all reported discrepancies to the Ap parametrization, this unverified assumption is load-bearing.

    Authors: We acknowledge that the manuscript does not present new cross-validation of the theoretical pitch-angle distributions against independent datasets such as FIREBIRD, BARREL, or Van Allen Probes for Ap > 40 or slot-region conditions. The PADs are taken from established quasi-linear theory of chorus and EMIC scattering as applied in prior POES-based studies. To address the concern we will revise the methods and discussion sections to include an expanded description of the assumptions, cite supporting literature on the theory's application to high-activity periods, and explicitly note the lack of direct validation under the strongest storm conditions. A full new cross-validation study lies outside the scope of this intercomparison. revision: partial

  2. Referee: [Results] Results (Ap > 40 regime): the claim that the Ap model reaches a plateau and therefore underestimates fluxes during strong storms rests on the accuracy of the theoretical-PAD reconstruction; without demonstrated robustness of that reconstruction under the same conditions, the reported bias cannot be unambiguously assigned to the CMIP6 parametrization.

    Authors: We agree that the attribution of discrepancies to the Ap parametrization depends on the reconstruction. The manuscript shows the Ap model saturating for Ap > 40 while the combined-detector estimates continue to increase and exhibit greater variability. In revision we will qualify the conclusions by adding explicit discussion of reconstruction uncertainties in the results section and by softening the language around sole attribution to the CMIP6 model, while retaining the observational comparison as evidence of a behavioral difference between the two approaches. revision: partial

standing simulated objections not resolved
  • New cross-validation against FIREBIRD, BARREL, or Van Allen Probes for Ap > 40 and slot-region events cannot be performed without substantial additional analysis not present in the original manuscript.

Circularity Check

0 steps flagged

No significant circularity; external intercomparison against independent data and theory

full rationale

The paper compares the existing CMIP6 Ap parametrization (derived in prior external work from 0° MEPED data) against loss-cone flux estimates constructed from dual-telescope counts plus pitch-angle distributions taken from established quasi-linear wave-particle theory. No parameters are fitted inside the target equations, no self-citation supplies the load-bearing uniqueness or ansatz, and the reconstruction is not defined in terms of the Ap model itself. The derivation chain therefore remains self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the domain assumption that theoretical pitch-angle distributions can be combined with the two MEPED telescopes to recover the loss-cone flux; no free parameters or invented entities are introduced in the abstract.

axioms (1)
  • domain assumption Electron pitch angle distributions from theory of wave-particle interactions can be used to estimate loss cone fluxes from the combination of 0° and 90° MEPED detectors.
    Invoked in the abstract to generate the loss-cone flux estimates used as the comparison benchmark.

pith-pipeline@v0.9.0 · 5863 in / 1303 out tokens · 43213 ms · 2026-05-25T16:03:53.549576+00:00 · methodology

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Reference graph

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