COSPAR, World Space Congress
Houston, TX, October 17-18, 2002
C4.3. Path toward Improved Ionosphere Specification and Forecast Models
Summary Report / Dieter Bilitza
The WSC session C4.3 was organized by the URSI/COSPAR Working Group on the International Reference Ionosphere (IRI) with the goal to review ongoing ionospheric modeling activities with a special emphasis on efforts that involve the IRI model. The session included 28 oral and 12 posters presentations. Unfortunately, two key speakers were unable to attend because of visa problems. Special meetings of the IRI Working Group to discuss the status of the IRI model and future improvements were held from 12:30 to 2:00 PM on October 17 and from 16:00 to 17:00 PM on October 18. Financial support was provide by COSPAR and URSI.
M. Friedrich (Austria) presented models for the quiet and disturbed auroral D region based on rocket and EISCAT measurements. The quiet-time model describes the changes at constant pressure surfaces in terms of solar zenith angle and solar activity (will be included in next version of IRI). The disturbed model additionally relies on riometer absorption measurements and Kp to describe D region changes during disturbed conditions. The nighttime E region (peak and valley) remains a problem because of the scarcity of data. For the F2 peak E. Araujo-Pradere (NOAA, USA) evaluated the new IRI storm-time correction model for foF2 with data from the worldwide ionosonde network for all storm events in 2000/2001. He finds an improvement of about 50% when using the new model instead of the uncorrected old model. For the F2 peak height, hmF2, comparisons at low latitude ionosonde stations in Africa (J., Adeniyi, Nigeria; O. Obrou, Ivory Coast), China (M. Zhang, CAS, Beijing) and South America (R. Ezquer, Argentina) showed that IRI underestimates the ionosonde-deduced heights by several tens of km.
D. Bilitza (GSFC, USA) presented a correction function for the IRI topside model that resulted in an excellent agreement with Alouette/ISIS topside sounder measurements. It was decided to include this corrected topside model as a new option in the next version of IRI. Shortcomings of the current IRI topside model were also noted in comparisons with electron densities deduced from CHAMP occultation measurements (N. Jakowski, Germany). B. Reinisch (UML, USA) presented an empirical plasmaspheric model based on data obtained from the Radio Probe Instrument (RPI) on the Image satellite. Other candidates for the IRI plasmasphere are the models by D. Gallagher (MSFC, USA), P. Webb (New Zealand), and T. Gulyaeva (Russia). Using data from Athens and Millstone Hill, A. Belahaki (Greece) showed that ground-based ionograms provide a reliable estimate of the electron density profile above the F2 peak. Using ROCSAT-1 data, S.-Y. Su (Taiwan) studied the occurrence of equatorial spread-F (ESF) in relation to the along-track density gradients and established thresholds above which ESF is very likely to occur.
Several new temperature models were introduced in this session. K. Oyama (Japan) presented electron temperature models for low-latitudes at 600 km based on Hinotori satellite data and for plasmaspheric altitudes based on Akebono satellite measurements. Millstone Hill incoherent scatter data from 1976 to 2001 were the basis for a station-specific model describing variations with time, altitude, season, and solar activity (S. Zhang, USA). K. Mahajan (India) used radar data from Arecibo to highlight the seasonal and solar cycle variations of electron temperature and the close correlation with electron density. One of the major shortcomings of the present IRI electron temperature model is the fact that it does not include variations with solar activity. An effort is planned to develop a new temperature model that will include these variations based on inputs from the various mission-specific and station-specific models (V. Truhlik, D. Bilitza, K. Oyama).
The current IRI ion composition model of the topside ionosphere was build with only a small amount of satellite und high-apogee rocket data. A new model has now been developed by V. Truhlik and L. Triskova (Czech Republic) based on Atmosphere Explorer C, D, E and Intercosmos 24 data. Comparisons with independent satellite data indicate a considerable improvement over the current IRI model. This new model will be implemented in the next version of IRI.
Efforts are underway to establish a quantitative description of ionospheric variability for inclusion in IRI. IRI would then in addition to the monthly mean also provide a measure for the potential deviation from this mean (standard deviation or quartiles). J. Minow (MSFC, USA) presented Ne and Te variability models based on a large amount of in-situ satellite measurements. The IRI Task Force Activity at ICTP has developed a first set of values using worldwide ionosonde data and focusing on the variability of ionospheric peak parameters. Two posters by M. Mosert (Argentina) et al. reviewed the variability of peak and profile parameters observed at several European and Argentine stations.
Data sources used included the IMAGE, ISIS, Alouette, Interkosmos 24, Picosat, Hinotori, ROCSAT-1, Akebono, Forte, CHAMP and GPS satellites, the EISCAT, Millstone Hill and Arecibo incoherent scatter radars, new and old ionosonde measurements, and compilations of rocket data and of data from older ionospheric satellites. An instrument with good potential for IRI work is the SCITRIS system for monitoring total electron content and ionsopheric scintillations that is scheduled for launch on the STPSAT1 and NPSAT1 satellites in 2006 (P. Bernhardt, NRL, USA).
R. Moses (LANL, USA) explained how transionospheric RF signals from lightning can provide information about the electron content along the path and discussed examples using FORTE satellite data. Occultation observation with GPS receivers on the Picosat and CHAMP satellites were discussed and evaluated by P. Straus (Aerospace Corp., USA) and N. Jakowski (Germany), respectively. The benefit of GPS observations for IRI was highlighted by M. Hernandez-Pajares (Spain) and P. Wielgosz (Poland).
B. Reinisch was elected as new Chair of the IRI Working Group and L. Triskova and M. Friedrich as URSI and COSPAR Vice-Chairs, respectively. IRI activities will be coordinated with the help of the IRI Steering Committee (SC). In addition to the IRI Chair and Vice-chairs the SC includes D. Bilitza and K. Rawer, who are former IRI Chairpersons and editors of the IRI-issues of Advances in Space Research, K.-I. Oyama, who is the editor of the IRI Newsletter, and S. Radicella, who organizes and hosts the annual IRI Task Force Activity at the International Center for Theoretical Physics in Trieste, Italy. Of particular interest to IRI members are the ongoing activities at the International Standardization Organization (ISO) to register an ISO standard model for the ionosphere. ISO had requested input from the IRI-WG regarding the current proposal, which is a modified IRI model that includes the Chasovitin-Gulyaeva plasmasphere and high-latitude models (SMI). The IRI group noted that there are now a number of good plasmasphere models and an overall evaluation is needed to determine which model should be included with IRI. In the meantime the IRI-WG recommended that the current ISO proposal be modified to only include the ionosphere and to only include the IRI-2000 model. It is also important to resolve potential copyright issues with ISO, because it is essential that IRI remains an open and freely available model.