| 21 Aug 2025
A comparison of modeled daytime E-regions from E-PROBED and PyIRI with ionosonde observations
Abstract. While the F-region is the primary focus of many ionospheric models because it contains the peak electron density, the E-region is an important region for ionospheric conductivities and high-frequency radio propagation. This study analyzes modeled E-regions from the newly developed PyIRI and E-PROBED models. A long-term comparison of E-region predictions from E-PROBED and PyIRI with ionosonde observations is performed for three sites spanning low- (Fortaleza, Brazil), mid-(El Arenosillo, Spain), and high-latitudes (Gakona, Alaska). Modeled foE and hmE trends are compared against a combination of manually-scaled and automatically-scaled ionograms using ARTIST-5 for the period 2009–2024 for El Arenosillo and Gakona, and 2015–2024 for Fortaleza. Measured and modeled virtual heights are compared for a subset of the ionograms through the use of a numerical ray-tracer. Overall, the models showed reasonable agreement with the ionosonde observations, with solar cycle, seasonal, and diurnal trends well captured for foE. E-PROBED generally overestimates foE with Mean Absolute Relative Errors (MRAEs) peaking around 70 % at dusk, while PyIRI showed close agreement with ionosonde foE resulting in MRAE peaks around 10 %. The hmE predictions showed weaker agreement, with a 15–20 km overestimate from E-PROBED when compared against auto-scaled ionograms, and a constant hmE prediction of 110 km for all times from PyIRI. However, manually-scaled hmE estimates show close agreement with E-PROBED predictions, indicating that great care must be taken when using auto-scaled hmE. Modeled virtual heights derived from E-PROBED and PyIRI show reasonable agreement with ionosonde observations, providing confidence in altitude-integrated electron density profiles. A slight bias exists between the modeled and measured virtual heights, and the direction of the bias reverses for manual- versus auto-scaled ionograms, demonstrating that auto-scaled uncertainties are also present in the virtual height observations. Overall, these results indicate that E-PROBED and PyIRI provide reasonable E-region estimates and may be used for practical applications that require modeled E-region parameters.
Reviewer Report for Emmons et al.
The present manuscript investigates the reproducibility of the ionospheric E-region as simulated by two recently developed models, PyIRI and E-PROBED, through comparative validation against ionosonde observations. The analysis encompasses three geographically distinct stations representative of different latitude regimes: Fortaleza, Brazil (low latitude); El Arenocillo, Spain (mid latitude); and Gakona, United States (high latitude). Long-term observational datasets spanning the interval from 2009 to 2024 were employed as the reference standard. The evaluation was conducted with respect to three fundamental parameters of the E-region: the critical frequency (foE), peak height (hmE), and virtual height.
The results indicate that both models are capable of reproducing solar cycle, seasonal, and diurnal variations in foE, with PyIRI exhibiting particularly strong consistency with observational data. In contrast, E-PROBED demonstrates a systematic overestimation of foE, most notably during dusk hours where the discrepancy becomes most pronounced. With regard to hmE, PyIRI is constrained by its constant altitude at 110 km, which makes it difficult to capture temporal or spatial variability of E-region. E-PROBED exhibits a mean overestimation of approximately 15 km, although comparison with manually scaled ionograms suggests relatively good performance. For virtual height, both models exhibit general agreement with ionosonde data, confirming the feasibility for estimating integrated electron density profiles within the E-region.
Overall, this study convincingly demonstrates both the strengths and limitations of PyIRI and E-PROBED, while simultaneously identifying issues related to automated scaling uncertainties and avenues for further model refinement. Clarification of certain aspects, particularly those related to figure presentation, the interpretation of dusk offsets, and the treatment of scaling discrepancies, would further enhance the clarity and readability of the manuscript. I therefore recommend publication subject to minor revisions after addressing the specific comments below: