Dieter Bilitza

International Reference Ionosphere 2000

The International Reference Ionosphere (IRI) is the international standard for the specification of ionospheric densities and temperatures. It was developed and is being improved-updated by a joint working group of the International Union of Radio Science (URSI) and the Committee on Space Research (COSPAR). A new version of IRI is scheduled for release in the year 2000. This paper describes the most important changes compared to the current version of IRI: (1) an improved representation of the electron density in the region from the F peak down to the E peak including a better description of the F1 layer occurrence statistics and a more realistic description of the low-latitude bottomside thickness, (2) inclusion of a model for storm-time conditions, (3) inclusion of an ion drift model, (4) two new options for the electron density in the D region, and (5) an improved model for the topside electron temperatures. The outcome of the most recent IRI Workshops (Kuhlungsborn, 1997, and Nagoya, 1998) will be reviewed, and the status of several ongoing task force activities (e.g., efforts to improve the representation of electron and ion densities in the topside ionosphere and the inclusion of a plasmaspheric extension) will be discussed. A few typical IRI applications will be highlighted in section 6.

International reference ionosphere — past, present, and future: I. Electron density

The most important investigations leading to the International Reference Ionosphere 1990 (IRI-90) are overviewed, and the latest version of the model is described. The shortcomings and limitations of the IRI-90 are pointed out, together with the ways of overcoming them. The list of studies that the IRI group has yet to carry out includes the investigations of magnetic storm effects as the highest priority. This paper discusses determinations of and the available data on the electron density, plasma temperatures, ion composition, and ion drift in the ionosphere, together with future improvements needed on these parameters.

International reference ionosphere—Status 1995/96

Abstract This paper describes the 1995/1996 status of IRI activities listing the improvements/additions that are currently being implemented. It also reports about a special IRI Task Force effort at the International Center for Theoretical Physics focusing on a better description of the “intermediate region“ (bottomside and F1). IRI modelling efforts are also continuing in the topside ionosphere. Better representations of the region above the F peak are of critical importance for many investigations/applications that require Total Electron Content (TEC) predictions. We will briefly report about efforts at GSFC to make Alouette/ISIS topside sounder data available for the modelling community. Reliability and accuracy of model predictions can be considerably increased through updating with real-time measurements. IRI has for some time had the facility of updates with co-located simultaneous F peak parameters (foF2, NmF2, hmF2, M(3000)F2). To expand this capability, updating algorithms are now under development that will allow updates with available peak parameters and/or Total Electron Content (TEC) measurements.

INTERNATIONAL REFERENCE IONOSPHERE 2000: EXAMPLES OF IMPROVEMENTS AND NEW FEATURES

This paper describes the changes that were implemented in the new version of the COSPAR/URSI International Reference Ionosphere (IRI-2000). These changes are: (1) two new options for the electron density in the D-region, (2) a better functional description of the electron density in the E-F merging region, (3) inclusion of the F1 layer occurrence probability as a new parameter, (4) a new model for the bottomside parameters B0 and B1 that greatly improves the representation at low and equatorial latitudes during high solar activities, (5) inclusion of a model for foF2 storm-time updating, (6) a new option for the electron temperature in the topside ionosphere, and (7) inclusion of a model for the equatorial F region ion drift. The main purpose of this paper is to provide the IRI users with examples of the effects of these changes.

EQUATORIAL F2-PEAK PARAMETERS,IN THE IRI MODEL

We have used measurements of an ionosonde station near the magnetic equator in Ouagadougou, Burkina Faso to evaluate the ability of the International Reference Ionosphere (IRI) model to correctly represent ionospheric F2 peak parameters in this region. The data represent conditions of high and low solar activity. Comparing the URSI and CCIR option for the F2 plasma frequency, foF2, we find that for low solar activity both options agree quite well with the ionosonde foF2 values and overall the CCIR maps show a slightly better fit. During high solar activity discrepancies are found during nighttime and the URSI maps providing the overall better fit. The measured F2 peak height values, hmF2, are compared on one hand with IRI predictions that are obtained based on the CCIR model for the propagation factor M(3OOO)F2 and on the other hand with the ionosonde-measured M(3OOO)F2 values. As expected using the measured values results in more accurate predictions. It is important to note that with the measured M(3OOO)F2 values IRI predicts the characteristic post-sunset that is seen in the measurements but not in the IRI predictions with the CCIR-M(3OOO)F2 model. 0 2003 COSPAR. Published by Elsevier Science Ltd. All

Global 3-D ionospheric electron density reanalysis based on multisource data assimilation

[1] We report preliminary results of a global 3-D ionospheric electron density reanalysis demonstration study during 2002–2011 based on multisource data assimilation. The monthly global ionospheric electron density reanalysis has been done by assimilating the quiet days ionospheric data into a data assimilation model constructed using the International Reference Ionosphere (IRI) 2007 model and a Kalman filter technique. These data include global navigation satellite system (GNSS) observations of ionospheric total electron content (TEC) from ground-based stations, ionospheric radio occultations by CHAMP, GRACE, COSMIC, SAC-C, Metop-A, and the TerraSAR-X satellites, and Jason-1 and 2 altimeter TEC measurements. The output of the reanalysis are 3-D gridded ionospheric electron densities with temporal and spatial resolutions of 1 h in universal time, 5 in latitude, 10 in longitude, and 30 km in altitude. The climatological features of the reanalysis results, such as solar activity dependence, seasonal variations, and the global morphology of the ionosphere, agree well with those in the empirical models and observations. The global electron content derived from the international GNSS service global ionospheric maps, the observed electron density profiles from the Poker Flat Incoherent Scatter Radar during 2007–2010, and foF2 observed by the global ionosonde network during 2002–2011 are used to validate the reanalysis method. All comparisons show that the reanalysis have smaller deviations and biases than the IRI-2007 predictions. Especially after April 2006 when the six COSMIC satellites were launched, the reanalysis shows significant improvement over the IRI predictions. The obvious overestimation of the low-latitude ionospheric F region densities by the IRI model during the 23/24 solar minimum is corrected well by the reanalysis. The potential application and improvements of the reanalysis are also discussed.

New B0 and B1 models for IRI

Abstract The electron density profile in the F region bottomside is described in the International Reference Ionosphere (IRI) by two parameters: a thickness parameter B 0 and a shape parameter B 1. The models used for B 0 and B 1 in IRI are based on ionosonde data from magnetic mid-latitude stations. Comparisons with ionosonde data from several stations close to the magnetic equator show large discrepancies between the model and the data. We propose new models for B 0 and B 1 based on data from several ionosondes including low and mid latitude stations. Close to the magnetic dip equator the new B 0 model provides an improvement over the current IRI model by a factor of up to 1.5.

EQUATORIAL F2-LAYER PEAK HEIGHT AND CORRELATION WITH VERTICAL ION DRIFT AND M(3000)F2

Ionosonde data recorded at Korhogo, Ce Longitude - 5.4, Dip -0.67) during a year of low solar activity (1995) were used to investigate ways of improving the representation of equatorial F2 peak height (hmF2) in the International Reference Ionosphere (IRI). For this purpose we have studied the correlation between hmF2 and the equatorial F region vertical drift as given by the model of Scherliess and Fejer (1999). The positive correlation found during nighttime could be helpful in representing the post-sunset peak of hmF2 that is currently not represented by IRI. We have also investigated the reliability of the CCIR model for the propagation factor M(3OOO)F2 model since the IRI hmF2 model is based on the strong anti-correlation between hmF2 and M(3OOO)F2. Overall the CCIR model represents the diurnal variation of M(3OOO)F2 quite well but does not represent small-scale features. With the M(3OOO)F2 values deduced from the Korhogo ionograms as input, the IRI hmF2 model provides an excellent representation of the observed diurnal structure including the post-sunset peak.

Combining GPS measurements and IRI model values for space weather specification

Abstract We will discuss various ways in which the International Reference Ionosphere (IRI) model and ionospheric data deduced from GPS measurements can be combined to improve ionospheric determinations. A number of research groups are analyzing GPS data products and providing global maps of vertical Total Electron Content (TEC) on a regular basis. IRI predictions can guide the interpolation of regional TEC estimations, computed from GPS data, to obtain global TEC maps. GPS measurements, on the other hand, can be used to update the IRI monthly averages to actual conditions. This can be done by using the GPS-derived TEC maps or by using the actual GPS measurements of the electron content along the signal path from satellite to ground receiver. We will discuss the updating results using the actual GPS measurements.

International Reference Ionosphere: Plasma densities - Status 1988

Abstract We discuss the changes and improvements that have been proposed for the IRI electron density profile and report on the status of the implementation of these corrections and new options. A fully analytical profile function Is intended for the whole Ionosphere. This can be achieved with a linear combination of several LAY functions. Whereas four LAY functions are needed to describe the density features of the middle ionosphere. three LAY-functions are sufficient for reproducing the electitn density in the topside ionosphere and in the lower Ionosphere. We indicate how the LAY parameters can be computationally obtained from characteristic profile points.