Elsevier

Advances in Space Research

Volume 55, Issue 8, 15 April 2015, Pages 1914-1927
Advances in Space Research

The International Reference Ionosphere – Status 2013

https://doi.org/10.1016/j.asr.2014.07.032Get rights and content

Abstract

This paper describes the latest version of the International Reference Ionosphere (IRI) model. IRI-2012 includes new models for the electron density and ion densities in the region below the F-peak, a storm-time model for the auroral E-region, an improved electron temperature model that includes variations with solar activity, and for the first time a description of auroral boundaries. In addition, the thermosphere model required for baseline neutral densities and temperatures was upgraded from MSIS-86 to the newer NRLMSIS-00 model and Corrected Geomagnetic coordinates (CGM) were included in IRI as an additional coordinate system for a better representation of auroral and polar latitudes. Ongoing IRI activities towards the inclusion of an improved model for the F2 peak height hmF2 are discussed as are efforts to develop a “Real-Time IRI”. The paper is based on an IRI status report presented at the 2013 IRI Workshop in Olsztyn, Poland. The IRI homepage is at IRImodel.org.

Introduction

The International Reference Ionosphere (IRI) is an international project that was initiated by the Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI) with the goal of establishing a standard representation of the plasma parameters in Earth’s ionosphere. Such a model of the ionosphere is important for the many applications that rely on electromagnetic waves traveling through the ionosphere including telecommunication, GPS, earth observation from space (e.g., satellite altimetry), radio astronomy and many more, because all of these applications need to correct for the retarding and refractive effect of the ionosphere on the probing signal. At the request of COSPAR and URSI, IRI is an empirical model being based on the majority of the available and reliable ground and space observations and avoiding as much as possible dependence on the still evolving theoretical understanding. But theoretical considerations can be helpful in bridging data gaps and for internal consistency checks. COSPAR’s prime interest in IRI is as a general description of the ionosphere as part of the terrestrial environment for the evaluation of environmental effects on spacecraft and experiments in space. URSI’s prime interest is in the electron density part of IRI for defining the background ionosphere for radiowave propagation studies and applications. With COSPAR and URSI the IRI project has the backing from the major international unions representing space-based ionospheric observations (COSPAR) and ground-based ionospheric observations (URSI). IRI development has benefitted greatly from the synergism between these two communities that are represented about evenly in the IRI Working Group and during bi-annual IRI Workshops. The current membership roster of the IRI Working Group is listed in Table 1. Progress of the IRI project is documented in several dedicated issues of the journal Advances in Space Research with selected papers from these workshops (see http://irimodel.org/docs/asr_list.html for references). The model has undergone a continuous improvement process that resulted in the release of major new editions of the model about every five years (Rawer et al., 1975, Rawer et al., 1978, Rawer et al., 1978, Rawer et al., 1981, Bilitza, 1986, Bilitza, 1990, Bilitza, 1997, Bilitza, 2001, Bilitza and Reinisch, 2008).

An important goal of geospace science is to develop predictions and forecast capabilities in support of human presence and technical endeavors in geospace. Data-based models like IRI are an important element of this undertaking because they compress the large volume of observational evidence in mathematical form combining different data sources and different techniques. One particular advantage over theoretical models is the very fact that they do not depend on the evolving theoretical understanding of the heliospheric environment. There are several examples where effects were already included in IRI before they were fully understood and included in theoretical models. One example is the distinct longitudinal variation with 4 maxima (wave number 4 structure) of the F-peak electron density that was first reported by Benkova et al. (1990) based on Interkosmos 19 topside sounder data and later with IMAGE/EUV observations (Immel et al., 2006), and then confirmed with data from CHAMP (Lühr et al., 2007) and TOPEX (Scherliess et al., 2008). While theoretical models still struggle to include this phenomenon in their modeling framework, IRI already includes a smoothed version of this phenomenon (McNamara et al., 2010); a smoothing effect is to be expected since IRI is based on monthly averages. Other examples are the midlatitude evening anomaly (Weddell Sea anomaly) observed by the Super Dual Auroral Radar Network (SuperDARN) radars that is well captured by IRI (de Larquier et al., 2011) and the occurrence of ionospheric plasma caves under the Equatorial Ionization Anomaly (EIA) (Lee et al., 2012).

A disadvantage of empirical models is the strong dependence on the underlying data base. Regions and time periods not well covered by the data base will result in diminished reliability of the model in these areas. So, for example, conditions during the most recent solar minimum in 2008/2009 were very different from earlier minima. The minimum was lower and more extended than earlier minima and as a result IRI being built with the data from earlier minima overestimated the plasma densities during the minimum period (Lühr and Xiong, 2010, Bilitza et al., 2012).

In this article we will first present the changes that led to IRI-2012 version of the model and then will discuss two important activities towards future improvements: a better representation of the F peak height hmF2 and the development of a Real-Time IRI.

Section snippets

IRI-2012

The latest version of the IRI model, IRI-2012, includes several important improvements and new additions that lead to a more accurate representation of (1) the electron density and ion composition in the region from the F2 peak down to the E peak, (2) the solar cycle variation of the electron temperature, (3) the storm effects in the auroral E-region, and will for the first time include the representation of auroral oval boundaries and their magnetic storm induced movement to lower latitudes.

Ongoing activities towards future improvements of IRI

Comparisons with IRI are often one of the first data evaluation tasks when a new data source becomes available. The goal is to compare the new ground or space data set with the prior empirical evidence accumulated in the IRI model. When consistent discrepancies are found and the reliability of the data is confirmed then efforts begin to improve IRI with this new data source. A number of IRI improvement efforts are currently underway we will focus here only on the two most important ones: a more

Conclusions

This paper is based on a status report given at the 2013 IRI Workshop in Olsztyn, Poland. It reviews the changes that were introduced with the release of the IRI-2012 version of the model and discusses two important ongoing activities, an improved representation of the F-peak height hmF2 and the development of a Real-Time IRI. IRI continues to evolve and IRI users will benefit from the many improvements introduced with IRI-2012:

  • (a)

    A new model for the bottomside electron density resulting in a 32%

Acknowledgments

IRI is the result of modeling efforts by IRI Working Group members. All these contributions are essential for the IRI success and are highly acknowledged by the author. I also want to acknowledge the many users of the model who have provided valuable feedback. A special thank you to Man-Lian Zhang who provided the Hainan ionosonde data used in Fig. 1.

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