Volume 14, Number 3, September 1998
By Dieter Bilitza
The International Reference Ionosphere (IRI) is a joint project of the Committee of Space Research (COSPAR) and the International Union of Radio Science (URSI). IRI is the international standard for the representation of ionospheric temperatures and densities. Since 1992 the IRI Working Group, a team of two dozen ionospheric experts, has been headed by Dieter Bilitza (NSSDC/RSTX). The model is the most frequently requested model out of the NSSDC models archive. (Roughly one third of the approximately 3,000 accesses to the FTP site per month are for the IRI model.) IRI can be run on line using the NSSDC-developed Web interface.
Several research groups are involved worldwide in efforts to improve the IRI model. Results and recommendations are presented during annual workshops and the Working Group decides then which changes and additions should be included in the next version of the model. The last meeting was held during the COSPAR Scientific Assembly in Nagoya, Japan, this summer. This article briefly lists the most important ongoing activities and the decisions made at the Nagoya meeting.
A major improvement of the IRI electron density profile in the middle ionosphere was accomplished through a special task force activity at the International Center for Theoretical Physics (ICTP) in Trieste, Italy, under the leadership of S. Radicella (ICTP), B. Reinisch (University of Massachusetts at Lowell) and D. Bilitza (NSSDC/RSTX). Based on ionosonde data from low latitudes the new model provides an improvement of 30% and more at the magnetic equator. The topside will be the next focus of this task force activity. Inclusion of a plasmaspheric model has been on the IRI agenda for some time. First M. Rycroft (U.K.) and then I. Kimura (Japan) have spearheaded IRI activities in this direction. A likely candidate for the first IRI plasmaspheric model is that developed by D. Gallagher based on DE 1 data.
In the lower ionosphere the IRI team has been very active and has benefited from modeling efforts in Russia (A. Danilov), Austria (M. Friedrich), Switzerland (E. Kopp), and Germany (W. Singer). Compilation of rocket data are the prime data base in this region. Indirect measurements from the ground are helping to resolve issues related to seasonal and solar cycle variations. Because of the data scarcity and the sometimes conflicting results, discussions have been often heated, and the group now has decided to allow three different options (models by Friedrich et al., Danilov et al., and Mechtley and Bilitza) for the representation of electron densities in the D region. The last of these is the default for many purposes, although descriptions and comparisons of these models will be available.
K. Oyama (Japan) is using in situ data from several Japanese satellites to investigate shortcomings of the IRI temperature model and ways to overcome them. As a result of his efforts the next version of IRI will include an improved electron temperature topside model. Triskova (Czech Republic) and her collaegues are in the process of mining the large data base from the Russian Interkosmos satellite series for IRI.
High on the wishlist of IRI users are (1) updating with measurements (in real- or post-time), (2) inclusion of storm effects, and (3) description of parameter variability. Great progress has been made on the first two topics. A. Komjathy (University of Colorado, Boulder) has developed an algorithm for updating IRI with GPS data. T. Fuller-Rowell's (Space Environment Center, NOAA) stormtime-updating algorithm is now scheduled to be included in the next version of IRI. Topic (3) will be focus of the 1999 IRI Workshop which will be held at the University of Massachusets in Lowell August 9 -12, 1998.