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.