Performance of Solar Proxy Options of IRI-Plas
Model for Equinox Seasons
, Tamara L. Gulyaeva
, and Feza Arikan
Department of Electrical and Electronics Engineering, Hacettepe University, Ankara, Turkey,
IZMIRAN, Moscow, Russia
International Reference Ionosphere (IRI) is the most acclaimed climatic model of the ionosphere.
Since 2009, the range of the IRI model has been extended to the Global Positioning System (GPS) orbital
height of 20,000 km in the plasmasphere. The new model, which is called IRI extended to Plasmasphere
(IRI-Plas), can input not only the ionosonde foF2 and hmF2 but also the GPS-total electron content (TEC).
IRI-Plas has been provided at www.ionolab.org, where online computation of ionospheric parameters is
accomplished through a user-friendly interface. The solar proxies that are available in IRI-Plas can be listed as
sunspot number (SSN1), SSN2, F10.7, global electron content (GEC), TEC, IG, Mg II, Lyman-α, and GEC_RZ. In
this study, ionosonde foF2 data are compared with IRI-Plas foF2 values with the Consultative Committee
International Radio (CCIR) and International Union of Radio Science (URSI) model choices for each solar proxy,
with or without the GPS-TEC input for the equinox months of October 2011 and March 2015. It has been
observed that the best ﬁtting model choices in Root Mean Square (RMS) and Normalized RMS (NRMS) sense
are the Jet Propulsion Laboratory global ionospheric maps-TEC input with Lyman-α solar proxy option for
both months. The input of TEC deﬁnitely lowers the difference between the model and ionosonde foF2
values. The IG and Mg II solar proxies produce similar model foF2 values, and they usually are the second and
third best ﬁts to the ionosonde foF2 for the midlatitude ionosphere. In high-latitude regions, Jet Propulsion
Laboratory global ionospheric map-TEC inputs to IRI-Plas with Lyman-α, GEC_RZ, and TEC solar proxies are
the best choices. In equatorial region, the best ﬁtting solar proxies are IG, Lyman-α, and Mg II.
The ionosphere plays a signiﬁcant role in Space Weather. The coupling of interplanetary and solar radiation
and solar wind from above, and the gravitational and seismic activity from below, shapes the structure of the
ionosphere. It is very important to model the trend and the variability of ionosphere due to their impact on
space and ground based communication, navigation, and positioning systems.
International Reference Ionosphere (IRI) is an international joint project of the Committee on Space Research
and the International Union of Radio Science (URSI), and it is dedicated to develop the climatic model of the
ionosphere since 1970s (Bilitza, 2001; Bilitza et al., 1993a, 1993b, 2011; Rawer et al., 1978). The IRI model pro-
vides ionospheric parameters such as electron density proﬁle, ion and electron temperatures, critical frequen-
cies, and maximum ionization heights of ionospheric layers (irimodel.org). The empirical and deterministic
model has been developed over the years with an intense collaborative effort in studies including but not
limited to Araujo-Pradere et al. (2004), Bilitza (2005), Bilitza & Reinisch (2008), Bilitza (2015), Galkin et al.
(2012), Maltseva et al. (2010), Oyeyemi and McKinnell (2008), and Wilkinson (2004), and it has been accepted
as the international standard in 2014 by the International Standardization Organization (ISO) (Gulyaeva &
Bilitza, 2012). The most recent version of IRI includes two new model options for the peak ionization height
of F2 layer, hmF2, and a revised representation of topside ion densities at very low and high solar activities
(Bilitza et al., 2017).
Since 2009, the vertical range of IRI model has been extended from 2,000 km to 20,000 km, the orbital height
of Global Positioning System (GPS) satellites. The new model, which can input total electron content (TEC)
values as well as F2 layer critical frequency, is called IRI extended to Plasmasphere (IRI-Plas) (Gulyaeva,
2011, 2012; Gulyaeva et al., 2011). The IRI model (and the IRI-Plas as one of the extensions to the plasma-
sphere) has been reinstated by ISO (ISO 16457:2014) as given in https://www.iso.org/standard/61556.html
in 2014. It has been shown in the literature that the assimilation of TEC into the model improves the repre-
sentation of current ionospheric state signiﬁcantly (Adebiyi et al., 2016, 2017; Bolaji et al., 2017; Ezquer
et al., 2017; Maltseva et al., 2013, 2015; Panda et al., 2015; Zakharenkova et al., 2015). The IRI-Plas model is
available at http://ftp.izmiran.ru/pub/izmiran/SPIM/ as a FORTRAN code.
SEZEN ET AL. 1441
Journal of Geophysical Research: Space Physics
• The online IRI-Plas model offers
automatic input of GIM-TEC and nine
new solar proxy options
• The model foF2 and hmF2 values are
compared with those of ionosondes in
midlatitude, high-latitude and
• Globally, GIM-TEC inputs with IG, Mg II,
or Lyman-alpha proxies provide the
smallest difference for foF2
Sezen, U., Gulyaeva, T. L., & Arikan, F.
(2018). Performance of solar proxy
options of IRI-Plas model for equinox
seasons. Journal of Geophysical
Research: Space Physics, 123, 1441–1456.
Received 10 NOV 2017
Accepted 18 JAN 2018
Accepted article online 23 JAN 2018
Published online 10 FEB 2018
©2018. American Geophysical Union.
All Rights Reserved.