The International Reference Ionosphere Model: A Review and Description of an Ionospheric Benchmark

Abstract

The terrestrial ionosphere is a plasma, that is, an ionized gas consisting of free electrons and ions. It is part of the Earth's atmosphere and is produced by solar radiation ionizing the neutral gas constituents. Only a small fraction of the neutral atmosphere is ionized. Typical ratios of electron to neutral gas density are 10 −2 at the top of the ionosphere (at a height of about 1,000 km), 10 −3 at the height of the ionospheric absolute electron density maximum (located roughly between 200 and 450 km of height), and 10 −8 at the bottom of the ionosphere (at a height of about 100 km). These limits mark the altitude boundaries of the ionosphere but they must not be considered fixed. They are highly variable in both space and time, in particular this is the case for the upper limit which marks the separation between the ionosphere below it and the plasmasphere above it (

What to Do When the F10.7 Goes Out?

“…The use of Equation 4is not a problem in NeQuick as users input an F10.7 value that is then converted to R12 v1 ; however in the IRI, both F10.7 and R12 v1 are required by various submodules (e.g., F10.7 used by , Shubin (2015), Fejer et al (2008) and R12 v2 by Altadill et al (2013) and Scotto et al (1997) [for a complete list see Table 8 of Bilitza et al (2022)]). Returning to our previous example of the behavior of the IRI during the March 2022 F10.7 interruption, one could attempt to mitigate the errors caused by the reversion to the NOAA F10.7 forecast by applying one of the many relationships above to determine a synthetic F10.7 that could be manually inputted with the model call.…”

“…The solar radio flux at 10.7 cm, known as F10.7, is one of the most commonly used indices of solar activity. It is used to drive both statistical and first principles models of the ionosphere and thermosphere and finds use in a wide range of applications spanning radio communications and navigation modeling (e.g., Warrington et al., 2009; ITU‐R P.2297‐0, 2013; Datta‐Barua et al., 2014; Themens et al., 2021), remote sensing (e.g., Yeo et al., 2015; Ruck & Themens, 2021; Thomas & Shepherd 2022), solar physics (e.g., Tapping & Morgan, 2017; Brooks et al., 2017), and space environment climate and modeling (Matthes et al., 2017; Chapman et al., 2018; Kodikara et al., 2018; Elvidge & Angling, 2019; Nugent et al., 2020; Bilitza et al., 2022). F10.7 is used as a proxy for the solar extreme ultraviolet (EUV) forcing of the upper atmosphere and has been measured since 1947 (K. F. Tapping, 2013).…”

What to do when the F10.7 goes out?

“…The use of Equation 4is not a problem in NeQuick as users input an F10.7 value that is then converted to R12 v1 ; however in the IRI, both F10.7 and R12 v1 are required by various submodules (e.g. F10.7 used by Danilov et al (1995), Shubin (2015), Fejer et al (2008) and R12 v2 by Altadill et al (2013) and Scotto et al (1997) [for a complete list see Table 8 of Bilitza et al (2022)]). Returning to our previous example of the behaviour of the IRI during the March 2022 F10.7 interruption, one could attempt to mitigate the errors caused by the reversion to the NOAA F10.7 forecast by applying one of the many relationships above to determine a synthetic F10.7 that could be manually inputted with the model call.…”

“…Warrington (2009), ITU-R P. 2297-0 (2013), Datta-Barua (2014), Themens and Jayachandran (2016)), remote sensing (e.g. Yeo et al (2015), Ruck and Themens (2021), Thomas and Shepherd (2022)), solar physics (Tapping and Morgan (2017), Brooks et al (2017)), and space environment climate and modelling (Matthes et al (2017), Chapman et al (2018), Kodikara et al (2018), Elvidge and Angling (2019), Nugent et al (2020), Bilitza et al (2022)). F10.7 is a proxy for the solar extreme ultraviolet (EUV) forcing of the upper atmosphere and has been measured since 1947 (K. F. Tapping, 2013).…”

“…Without redundant systems, many critical space weather architectures suddenly become unavailable, or, perhaps worse, generate output using "default values" of F10.7 (for example an F10.7 of 100) which can also be used for forcings in forecasts, potentially producing substantial errors without suitable warnings. For example, both the International Reference Ionosphere (Bilitza et al, 2022) and the Empirical Canadian High Arctic Ionospheric Model (Themens et al, 2017) immediately revert to the use of NOAA long-term F10.7 forecasts if measured values are not available. On March 18 th , 2022, resorting to these forecasts constituted an immediate error of ~14 sfu, increasing to an error of ~70 sfu just ten days later as an active region rotated onto the disk.…”