IRI/COST Workshop, Prague, Czech Republic, July 10-14, 2007

 

Ionosphere – Modelling, Forcing, and Telecommunications

 

Dieter Bilitza

 

The workshop continued the bi-annual meetings that the COSPAR/URSI Working Group on the International Reference Ionosphere (IRI) organizes in years between the COSPAR General Assemblies. These workshops are the prime venue for discussions of model shortcomings, improvements, new model additions, applications, and other IRI-related topics. These meetings have grown from small gatherings of experts to well-attended workshops with a good representation of the many countries involved in the IRI effort and a good balance between the different measurement techniques that are contributing to the IRI success. For the Prague Workshop the IRI team joined forces with the European Cooperation for the Mitigation of Ionospheric Effects on Radio Systems (COST 296) one of the major pan-European projects in ionospheric physics supported by the European Cooperation in the Field of Scientific and Technical Research (COST). The special focus of this combined IRI/COST workshop was a better representation of the forcing from below and from above in ionospheric models with special emphasis on the IRI model and regional European models. Naturally the workshop had a strong orientation towards application of ionospheric models and specifically on their effects on radio systems. The meeting was expertly organized by the Local Organizing Committee (Lastovicka, Buresova, Sauli, Truhlik, Triskova) whose untiring effort not only made this a very productive meeting but also a memorable time for everybody in the Golden City including an excursion to the beautiful Konopiste Castle.

               The workshop was attended by 103 participants from Africa, Asia, Europe, and North and South America. 67 oral and 50 poster papers were presented. The agenda included sessions on Ionospheric Effects on Radio Systems, GPS and TEC, Topside, Ionospheric Storm Effects, Ionospheric Sounding, F Peak Mapping, Bottomside and E-Region, the IRI Final Discussions, and the COST296 Management Committee meeting. Papers and posters from the meeting will be considered for a special issue of Advances in Space Research.

               The meeting was financially supported by COSPAR, URSI, IAGA, the European Office of Aerospace Research & Development (EOARD) of the US Air Force, the US Office of Naval Research (ONR), and the Czech Academy of Sciences, providing travel funds (full or partial) for 14 scientists from Argentina, China, Georgia, India, Iraq, and Turkey.  

 

F-PEAK MAPPING

 

Increased accuracy of models for the F-peak parameters (foF2, NmF2, hmF2, M(3000)F2) is an important goal of both IRI and COST. COST is primarily focussed on the European sector while IRI has to deal with the whole globe. Several modelling approaches were presented including Neural Networks (NN) (Yu, China; Y. Tulunay, Turkey; Habarulema, South Africa; Tomasik, Poland), Genetic Algorithms (F. Arikan, Turkey), Eigen-mode Analysis (Wan, China) and others. Very promising are NN models for foF2 and M(3000)F2 developed by McKinnell et al. (South Africa) that are trained with a large volume of ionosonde data. Comparisons with data not used in the training process show significant improvements versus the older CCIR and URSI models. It was decided to include their M(3000)F2 model in the next version of IRI to get a better representation of the hmF2 evening peak; the peak height hmF2 is correlated with the propagation factor M(3000)F3 that is routinely scaled from ionograms.  More work is still needed for the foF2 model in particular a more globally homogenous data base including data from more ionosondes (e.g., Brazilian and Chinese ionosondes are currently not included) and from topside sounder satellites. An important outcome of the Prague meeting is the forming of a special task group on F-peak mapping to bring together data providers and modellers and to facilitate inclusion of the improved models in IRI and in operational programs. The task group includes members from IRI and COST and is led by Bilitza (USA). A first task is to interact with the International Telecommunication Union -Radiocommunication (ITU-R) group whose proposal is to digitise the existing CCIR maps on a 2.5 degree latitude/longitude grid and to publish new maps every 5 years (Bradley, USA).

 

TOPSIDE AND TEC

 

Many of the GNSS-related presentations discussed the deduction of peak and profile information from the slant path phase and amplitude measurements using simple profile assumption or a more sophisticated tomographic approach. Difficulties remain in areas of large ionospheric gradients and/or scarce ground station coverage and also because of insufficient knowledge of the plasmaspheric contribution. The new constellation of COSMIC satellites carrying GPS receivers into space helps to overcome some of the coverage problems but has to deal with the inherent limitations of the radio occultation technique. Comparisons with Jicamarca incoherent scatter radar and ionosonde measurements, for example, showed that assimilating COSMIC and GPS data into the JPL/GAIM model led to improvements in the topside, but made results worse in the F layer (Rich, USA). Several presentations showed how using IRI as an a priori source of information, can lead to improvements in the tomographic construction of 3-D maps (O. Arikan, Turkey; Zeilhofer, Germany; Bhuyan, India). Good progress is made in accounting for higher order ionospheric effects (Hernandez-Pajares, Spain) and significant improvements are expected from the third frequency that will be standard with the European Galileo system (Spits, Belgium).

               IRI-2007 offers two new options for the topside electron density profile: NeQuick and a corrected IRI-2001. First evaluations of these new additions were inconclusive: A comparison with Alouette/ISIS topside sounder data favored the NeQuick option (Bilitza, USA) whereas an analysis with CHAMP and COSMIC data finds better agreement with the corrected IRI-2001 option (Mayer, Germany). IRI-2001-corr seems to include a more accurate representation of the spatial and altitudinal structure of the Equator Anomaly while IRI-NeQuick scores higher when data from all latitudes are considered.  NeQuick was also compared with GNSS data in China (J. Shi, China) and Europe (Bedaine, Belgium) and with regional models based on these data. Measurements from the Indian SROSS C2 satellite at ~500 km illustrate the close coupling of EA parameters with the equatorial electrojet (Bhuyan, India) and might help in further evaluating the two different options.

An important parameter for the representation of the topside electron density profile is the ionospheric scale height. Besides the standard plasma scale height that varies from an Oxygen scale height near the peak to a light ion scale height higher up, modelling often relies on the “vertical scale height” assuming an exponentially decaying profile or an “effective scale height” assuming a Chapman-type profile (L. Liu, China). Global models for this scale height and its variation with altitude are an area of study of several IRI and COST researchers presenting progress reports at this meeting (Kutiev, Bulgaria). 

 

BOTTOMSIDE

 

Comparisons of ionosonde (McKinnell, South Africa) and incoherent scatter radar data with IRI illustrated the shortcomings of the current tabular form of the representation of annual and global variations of the bottomside profile parameters (B0, B1, D1). The spherical harmonics approach by Altadill and Blanch (Spain) showed much better results and will be included in the next version of IRI.

The representation of ionospheric storm effects in IRI is currently limited to the F-peak density and IRI represents quite well the mostly negative ionospheric storm effects observed in mid-latitude summer (Buresova, Czech Republic). Inclusion of the storm-induced uplift of the layer (Reinisch, USA) is a high priority goal for future versions of IRI. A new effort is looking at a model description of E-region effects using more than 6 years of TIMED/SABER NO⁺(v) 4.3 μm Volume Emission Rate (VER) data, an excellent proxy for studying E-region chemistry (Mertens, USA).

 

PLASMA TEMPERATURES AND ION DRIFT

 

In the area of plasma temperatures accurate representation of solar cycle effects is a top priority. When combining incoherent scatter radar and DMSP satellite data towards this goal, significant discrepancies were found between the ground and space measurements at low solar activities, likely due to the low electron densities which make accurate electron temperature determination in the topside ionosphere difficult for both techniques. At lower altitudes a large database of satellite in situ measurements is being used to establish the average variation patterns of Te over the solar cycle for different local time, season, and latitude (Truhlik et al., Czech Republic).

The new equatorial zonal drift model of Fejer et al. (USA) based on Jicamarca incoherent scatter radar measurements was proposed for IRI and will be included in the next version complementing the already included vertical drift models by the same authors. The model includes dependences with solar activity and season and reproduces the observed westward daytime drifts and eastward nighttime drifts. A study of magnetic storm effects on the ion drift based on observations with the Pruhonice, Czech Republic digisonde shows dramatic increases in E and F region drifts at this mid-latitude station (Boska, Czech Republic). S.-Y. Su (Taiwan) used ROCSAT data to study the occurrence statistics of equatorial density irregularities and their correlation with vertical drift velocities

 

NEW INPUTS FOR IRI

 

Many of the COST-296-specific topics are also of great interest for IRI. A series of presentations reviewed the status and progress of these activities including HF communications (airplane, ship, HF radar, military; circuit diagnostics, frequency management), ionospheric scintillations, and ionospheric influence on performance of various GNSS-based systems. The objective in all cases is to mitigate the effects of the ionosphere on systems involved (e.g., loss of lock of GNSS receivers) (Bourdillon, France; Lastovicka, Czech Republic; Cander, U.K.; E. Tulunay, Turkey; Warnant, Belgium).. COST efforts to establish a good perturbation index have focussed on squared TEC rates and latitudinal TEC gradients (Jakowski, Germany).

Large-scale theoretical modelling will help to define the indices that are required to accurately include the forcing from below and above in IRI. Examples presented at this meeting are the new Integrated Dynamics through the Earth Atmosphere (IDEA) model of Fuller-Rowell et al. (USA) coupling a Whole Atmosphere Model (WAM) with Global Ionosphere-Plasmasphere (GIP) and electrodynamics models for studying and quantifying terrestrial weather effects, and the  Global Self-consistent Model for the Thermosphere-Ionosphere-Plasmasphere (GSM TIP) by Klimenko et al. (Russia) for studying the ionospheric effects of substorms and of a solar eclipse. Using CHAMP, TOPEX, IMAGE, TIMED, COSMIC, and GPS data Watanabe (Japan) and Talaat (USA) presented strong arguments for the need of a strong coupling of IRI with the middle and lower atmosphere. 

Statistical studies of the variation patterns of characteristic features in the low and high latitude ionosphere are a first important step towards including these features in IRI. At low latitudes studies are focused on the amplitude and width of the Equatorial Anomaly using GNSS (M.-L. Zhang, China), SROSS C2 (Bhuyan, India),  ROCSAT 1 and CHAMP satellite data, at high latitudes the focus is on the sub-auroral trough (Zaalov, U.K.) and modeling is based on GNSS (Krankowski, Poland) and DEMETER data (Rothkaehl, Poland).

               As always a large number of presentations compared the IRI model with local measurements and models. Al-Ubaidi (Iraq) found good agreement with measurements by the Al-Battani ionosonde near Baghdad (34.4,44.4) during 1989. Comparisons with the long record of ionosonde measurements in Hainan, China showed good agreement for foF2 and discrepancies for hmF2 (X. Wang, China).

Several years of MF radar (3.17 MHz) measurements of D-region electron densities with the Saura radar at Andoya island (69°N) should help to improve the representation of electron densities from 55 km to 90 km in IRI. The derived electron density profiles are in general agreement with results from insitu radio wave propagation experiments at Andenes as well as with observations by the EISCAT VHF radar at Tromsø  (Latteck, Germany).

 

MEMBERS, MEETINGS, PUBLICATIONS

 

Two new members were welcome into the IRI team. Dr. Wan Weixang from the Institute of Geology and Geophysics in Beijing, China brings with him his great expertise in  Eigen mode analysis of ionospheric parameters and he will help the IRI team with access to the Chinese ionosonde data. Dr. K.G. Ratovsky from the Institute of Solar-Terrestrial Physics in Irkutsk, Russia will take the place of Dr. E. Kazimirovsky (formerly at the same Institute) who is retiring after many years of service to the IRI project mostly in the area of ion drift measurements and modelling.

               A special 2-day IRI session was accepted for the 2008 COSPAR General Assembly in Montreal, Canada. The session is on the topic of IRI Updating and Data Assimilation. The next full IRI Workshop will be held near Kagoshima, Japan in 2009.  Dr. Watanabe gave a very enticing presentation about the location for the 2009 IRI Workshop, which will be held near Kagoshima, Japan, most likely in the fall (October). There are also plans for a Special Workshop on the Real-time IRI either in Fall of 2008 or Spring 2009 in Boulder, Colorado organized by Tim Fuller-Rowell and Eduardo Araujo.

               The accepted papers from the 2005 IRI workshop in Ebro, Spain were recently published as Volume 39, Issue 5 of Advances in Space Research with Reinisch, Bilitza, Altadill as the editors.