IRI 2005 Workshop:

New Satellite and Ground Data for IRI and Comparison with Regional Models

 

Report/ Dieter Bilitza

 

As part of its centennial celebrations, the Ebro Observatory in Roquetes, Spain, hosted the 2005 International Reference Ionosphere (IRI) Workshop. Workshop sessions, held at the Observatory and the Auditory Felip Pedrell in neighboring Tortosa from June 27 to July 1, covered the typical IRI topics: F-region Modeling, Bottomside Parameters and Drifts, Topside Ionosphere, IRI Applications, Temperature and Composition, Ionospheric Variability, Lower Ionosphere, Total Electron Content, and New Inputs for IRI. The agenda included 66 presentations by 48 scientists from 18 countries illustrating the global reach and importance of the IRI activities. Ground and space data sources were evenly represented including data from many ionosondes, and from most incoherent scatter radars, and from the satellites Akebono, CHAMP, DMSP, GPS, Hinotori, IK-19, IK-24, IMAGE, ISIS, JASON, Ohzora, ROCSAT, TIMED, TIROS/NOAA, and TOPEX, and from several rocket flights. The meeting benefited from the excellent local support under the leadership of Dr. David Altadill. The Observatory team not only patiently shepherded the international group of scientists during the session periods, but also arranged an evening walking tour of Tortosa and a conference excursion to the beautiful Tortosa-Beseit Natural Park and the Picasso Center in Orta de Sant Joan. Opening and closing ceremonies were attended by local and regional politicians who pledged their support for the Observatory and acknowledged the importance of holding this international science meeting in their town and region. Financial support was provided by the following organizations: Committee on Space Research (COSPAR), International Union of Radio Science (URSI), European Office of Aerospace Research and Development (EOARD) of the US Air Force Office of Scientific Research, Consejo Superior de Investigaciones Cientificas (CSIC), Ministerio de Educación y Ciencia (MEC), AgŹncia de Gestió d'Ajuts Universitaris i de Recerca (AGAUR) and by the Observatori de l'Ebre. Also the Mayor's Offices of the Towns of Roquetes and Tortosa, the Council of the Lower Ebro Area, La Caixa, the Ramon Llull University and Diario ABC supported this event.

 

 

Electron Density – Topside, Plasmasphere, and TEC

 

The new version of IRI, due to be released later this year, will include two options for the topside electron density: (1) the correction term for the current IRI model as proposed by Bilitza (USA) and (2) the newest version of the NeQuick model as presented by Coisson (Italy).

Reinisch (USA) explained his new approach of representing the topside and plasmasphere electron densities by a Chapman profile with continuously varying scale-height using the developing UML plasmasphere model that is based on IMAGE/RPI and ISIS measurements. Alternatively, Pulinets (Mexico) and Depuev (Russia) are proposing the use of an Epstein function with variable scale-height and have successfully applied this approach to their IK-19 topside sounder data. An important aspect of their model is the inclusion of persistent longitudinal features. Uemoto (Japan) presented Ohzora and Akebono topside sounder data as a possible source for improvements of the IRI topside profile. Plasmaspheric extensions of IRI were discussed by Coisson (Italy) and by Gulyaeva (Russia) using the Global Core Plasma Model (GCPM) developed by Gallagher et al. (USA). Garner (USA) found that binned DMSP data follow a lognormal distribution and he studied global and solar activity variations of the distribution parameters.

There were quite a number of presentations of TEC-related studies including: (1) Comparisons of GPS TEC with ionosonde ITEC measurements (McKinnell, South Africa; Mosert, Argentina), (2) Comparisons of TEC measurements with IRI predictions (Bhuyan, India; F. Arikan, Turkey; Moeketsi, South Africa; Opperman, South Africa). (3) Ionospheric tomography techniques and their utilization of IRI (O. Arikan, Turkey; Bhuyan, India; Opperman, South Africa), (4) Ionospheric data obtained by different dual-frequency space techniques and their use for improvements of IRI (Bilitza, USA), (5) An assessment of 2nd order ionospheric effects on GPS measurements (Hernandez-Pajares, Spain), (6) Using a wavelet/spline approach as an initial step of a multi-resolution representation of TEC (Schmidt, Germany) (6) A method for deducing foF2 from GPS-TEC (Krankowski, Poland).

 

Electron Density – F-peak and below

 

The main new input for the next version of IRI will be the spread-F occurrence model for the South-American sector that was developed by Abdu (Brazil) based on ionosonde data. Efforts are under way to develop a quantitative description of ionospheric variability in terms of quartiles and deciles for inclusion in IRI (Mosert, Argentina; Altadill, Spain).

In IRI the height of the F2 peak is computed from the M(3000)F2 factor that is regularly measured by ionosondes. A study by M. Zhang (China) showed that the shortcomings of IRI in representing the sunrise and post-sunset peaks in hmF2 are a result of the shortcomings of the CCIR model used for M(3000)F2. Good agreement is obtained when using the ionosonde-measured M(3000)F2. McKinnell (South Africa) reported about her effort in developing a neural network (NN) model for M(3000)F2, which could eventually replace the CCIR model and its shortcomings. The quality of IRI predictions during ionospheric storms was evaluated with a variety of ionosonde data (Mosert, Argentina; Araujo-Pradere, USA; Miro, Italy). Peronne (Italy) presented a storm-time modeling approach based on a time-weighted magnetic accumulation index. A validation of TIMED/GUVI nighttime electron density profiles with worldwide ionosonde data was presented by DeMajistre (USA). Good agreement was found for most stations making the GUVI profiles a promising new data source for IRI nighttime improvements.

The diurnal, seasonal, and solar cycle variations of bottomside profile parameters were studied by Mosert (Argentina) and by Blanch (Spain) based on ionosonde data with the goal of improving the current representation in IRI. Altadill (Spain) is proposing analytical functions to replace the current tabular form in which these parameters are provided in IRI. He also used such functions to represent vertical drift measurements from the Ebro digisonde.

E-region modeling is focusing on the auroral region and a representation of the enhanced foE due to particle precipitation (Fuller-Rowell, USA, NOAA/Tiros data; Mertens, USA; TIMED/SABER data). McKinnell (South Africa) is proposing a NN approach to modeling the density distribution in the auroral zone lower ionosphere.

            IRI currently includes Friedrich’s (Austria) FIRI model as a separate option for the D-region electron density only. But the model is forced to agree with the IRI E-peak. This results in E-region values that are quite different from the original data-based FIRI predictions. It was therefore decided to decouple the FIRI model option from the E-peak constraint and make it accessible all the way to 140 km.

 

Plasma Temperatures, Ion Composition, and Ion Drift

The next version of IRI will include several new inputs: (1) a model for the plasmaspheric electron temperature based on Akebono data (Kutiev, Bulgaria and Oyama, Japan), (2) the TTS model for the topside ion composition based on IK-24 and AE-C,-E data (Triskova and Truhlik, Czech Republic), (3) a model for the storm-time vertical ion drift (Scherliess and Fejer, USA).

Su (Taiwan) presented new models deduced from ROCSAT satellite data (high solar activity) describing the topside ion density, the distribution of density irregularity, the ion temperature, and the equatorial vertical ion drift. Empirical models for parameters from 7 incoherent scatter radars have been develop by S. Zhang (USA) in conjunction with the radar groups. This will be a valuable evaluation tool for the IRI model performance at the radar locations. Kutiev (Bulgaria) has combined his model for the topside ion transition height with his topside scale-height model to provide a topside profiler for ionosondes. Bilitza (USA) and Truhlik (Czech Republic) used a large data base of satellite in-situ measurements to investigate the altitudinal, latitudinal, and seasonal differences in the solar cycle variation of electron temperatures and densities and found good agreement when comparing the observed trends with those predicted by the FLIP model. They also tested various solar indices and found best results with F10.7 and PF10.7=(F10.7+F10.7A)/2 where F10.7A is the 81-day average. The IRI Te model currently does not include solar cycle variations. Other temperature features not currently included in the IRI model were also pointed out. Oyama (Japan) reminded participants that rocket observations of large differences between electron temperature and neutral temperature around 100 km are not yet explained and are not included in IRI. Watanabe (Japan) using CHAMP observations finds high electron densities around 70° latitudes at noon and enhanced thermospheric mass density and high electron temperature in the cusp region (75°-80°). The shortcomings of the IRI ion temperature and ion composition model in representing some characteristic longitudinal and diurnal features were noted by Chao (Taiwan) in comparisons of IRI with ROCSAT data.

 

Meetings, Publications, New Member

 

Selected papers from the 2003 IRI Workshop in Grahamstown, South Africa were published as Number 9 of Volume 34 of Advances in Space Research (ASR) including 35 contributions and a dedication and paper in honor of Prof. Karl Rawer’s 90th birthday. There was also a special session during the German National URSI meeting (Kleinheubacher Tagung) celebrating Karl Rawer and his contribution to the IRI effort. The papers from that session were published as the 2nd Volume of Advances in Radioscience (Kleinheubacher Berichte 2003). The reviewing process for the presentation from the 2004 IRI session during the COSPAR General Assembly in Paris, France is nearing completion and the dedicated ASR issue will be coming out later this year.

            The next IRI meeting will be held during the COSPAR General Assembly in Beijing, China (16-23 July, 2006) on the topic of “Solar Cycle Variations of Ionospheric Parameters”. On behalf of her Argentine colleagues M. Mosert invited the IRI team to consider holding a special IRI Workshop in Buenos Aires, Argentina in late 2006 recommending a TEC/GPS-related IRI meeting topic. Her proposal was received favorably and she will explore the financial and logistics issues connected to such a meeting. Buresova (Czech Republic) provided the participants with more information about the Institute of Atmospheric Physics in Prague, the venue for the 2007 IRI workshop. Possible dates were discussed including a coupling to the IUGG meeting in Perugia, Italy, from July 2 to 13, 2007.

            Prof. Shin-Yi Su from the Institute of Space Science and Center for Space and Remote Sensing Research of the National Central University in Chang-Li, Taiwan was elected as new member to the IRI Working Group.

 


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