the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 25 Feb 2026
Reevaluation of EISCAT plasma parameters during the May 2024 geomagnetic storm using O+ ratios from AMIE-driven SD-WACCM-X
Abstract. We present a reevaluation of EISCAT plasma parameters during the May 2024 geomagnetic storm, applying the ion composition from an AMIE-driven SD-WACCM-X simulation instead of the standard IRI model. This resulted in significant deviations of F1 region electron densities (up to 15 %), electron temperature (40 %), and ion temperatures (30 %) from the original analysis. Basic correlations of plasma parameter deviations and differences in ion composition indicate the possibility of deriving a correction model if the presented approach is extended to a large measurement database. Parameter uncertainties are also shown to be affected by the reevaluation (5 % – 10 %), and the general relations of parameter uncertainty, ion composition differences, and absolute ion composition profiles are investigated. It is shown that in the F1 region, the plasma parameter deviations are notably larger than the uncertainty range. Incorrect assumptions about the ion composition can have a significant impact on the accuracy of ISR measurements, and that has important consequences for the possible application of ISR data in data assimilation. Advantages and disadvantages compared to previously presented approaches regarding the ion composition issue are discussed. The main advantage of the presented method is that the physics-based background enables debiasing of EISCAT plasma parameters from standard analysis.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Annales Geophysicae.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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RC1: 'Comment on egusphere-2026-823', Anonymous Referee #1, 03 May 2026
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The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-823/egusphere-2026-823-RC1-supplement.pdfReplyCitation: https://doi.org/
10.5194/egusphere-2026-823-RC1 -
RC2: 'Comment on egusphere-2026-823', Anonymous Referee #2, 04 May 2026
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The manuscript is well written and covers an important topic for incoherent scatter radar (ISR) spectra fitting to obtain plasma parameters, specifically the ion composition estimate used when performing the spectra fits. By using a model run from WACCM-X the authors are able to improve the plasma parameter fits from the Guisdap software package during the May 2024 Superstorm using the EISCAT Svalbard 42m radar. There are 2 runs of the WACCM-X model, one driven by 'Heelis' which is effectively driven by the Kp-Index, and one driven by 'AMIE' which is data driven from an extensive set of different ionospheric and geomagnetic measurements. The authors only use the AMIE driven model when presenting the results.
The authors make suggestions to use the re-analysis technique on the larger EISCAT dataset. This is currently not reinforced by their analysis, though it could be with further analysis and information. The following further analysis is suggested:
1) Using WACCM-X with Heelis to obtain the plasma parameter fits and comparing the results with the WACCM-X AMIE driven model derived fits.
2) Using the full profile incoherent scatter fit provided in, e.g., Virtanen et al. 2021, and comparing with the results here. The study presented here is a perfect opportunity to compare the full profile fits to the model driven fits. This would be appreciated by the greater community, with hopefully good agreement between the methods. Virtanen et al., 2021, provides functions that should be usable in the Guisdap software, and it should not be an insurmountable amount of work to re-process this period of data with that software.
Virtanen, I. I., Tesfaw, H. W., Roininen, L., Lasanen, S., & Aikio, A. (2021). Bayesian filtering in incoherent scatter plasma parameter fits. Journal of Geophysical Research: Space Physics, 126, e2020JA028700. https://doi.org/10.1029/2020JA028700
3) Including a few days with different geomagnetic conditions to determine how the WACCM-X model driven ISR spectra fit results compare with the IRI model spectra fits during less geomagnetically active days.
It should be stated, that even without this additional analysis the manuscript still has merit. It is only that there is the potential for a much improved study that can be used as a basis for what techniques to use when determining ionospheric parameters from the incoherent scatter spectra when the ion composition is unknown.
Therefore, it is suggested that the authors either present the manuscript as is, and remove some of the suggestions without the proper validation of the statements, or provide an impactful study with some additional figures and comparisons that will be greatly appreciated by the community. It is for this reason that 'Major Revisions' has been suggested.
Please find comments corresponding to the specific lines below.
Lines 91-92: This manuscript is highlighting the re-analysis technique for ISR spectra fitting using the WACCM-X model, and in lines 91-92 it is even mentioned that the Heelis-driven model is more applicable to the re-analysis of the EISCAT measurements in general. The manuscript does not show any results from using the Heelis-driven WACCM-X model though, even though the authors have the data available. It is difficult to determine if the claims of using WACCM-X with Heelis-driving is suitable. Please include the results from Heelis-driven WACCM-X Guisdap spectra fitting and compare with the AMIE-driven WACCM-X Guisdap results.Lines 114-115: The scope of the paper is the May 2024 superstorm, but the manuscript argues for the technique to be applied to the general dataset. More days with different geomagnetic conditions should be investigated before making this claim.
Lines 168-169: It is claimed that a validation of BAFIM is difficult, but the data presented here is a great opportunity to compare the techniques and potentially validate both. BAFIM was developed for Guisdap and therefore should be able to be used in the ISR spectra fitting analysis without too much difficulty.
Lines 172-173: The correction function presented has not been sufficiently analysed for different geomagnetic conditions to know if it is suitable. And even then, it potentially only 'corrects' one parameter, T_e. The other parameters do not show such a linear response. Ideally, EISCAT would generate the different incoherent scatter spectra fits with well defined and documented input conditions and make those results available to the users.
Lines 188-189: It is stated that the Heelis-driven WACCM-X would have to be used for EISCAT ISR spectra corrections but there are no results presented from this, even though the authors have the data available. Further, there is a claim that the correction model would be applicable to all researchers but there are no results showing that such a correction model is viable for different geomagnetic conditions. Please expand the analysis to address these statements.
Citation: https://doi.org/10.5194/egusphere-2026-823-RC2
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