International Reference Ionosphere 2001 Workshop on the Low Latitude Ionosphere



Report / Dieter Bilitza



The 2001 IRI Workshop was held at the Instituto Nacional de Pesquisas Espaciais in São José dos Campos, Brazil in the week from June 25 to 29. It was attend by about 60 scientists including representatives from USA, Russia, India, Peru, South Africa, Japan,

Spain, Argentina, U.K., Czech Republic, Chile, and Brazil. The 75 papers were presented in 8 oral sessions and in 1 poster session. The titles of the oral sessions were: The Equatorial Anomaly Region, Total Electron Content and Topside, Description of Ionospheric Variability, Modeling the Low Latitude Ionosphere, Ion composition, Scintillation and Spread-F, Representation of F Peak and Bottomside Parameters, New Data and Model Inputs and Applications. The workshop opened with a welcome address by the INPE Director, V.W.J.H. Kirchhoff and was followed by an overview talk by D. Bilitza (USA) describing the new version of the IRI model, IRI-2001. The meeting was well prepared and organized thanks to the excellent efforts of the Local Organizers: J. H. A. Sobral, M.A. Abdu, and I.S. Batista. Financial support was provided by the Committee on Space Research (COSPAR), the International Union of Radio Science (URSI), the International Center for Theoretical Physics (ICTP), the Instituto Nacional de Pesquisas Espaciais/ Ministério da Ciência e Tecnologia (INPE/MCT), the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), the Sociedade Brasileira de Geofísica (SBGf), and the Fundação Coordenação de Aperfeiçoamento de Pessoal de Nível Superios (CAPES). The papers and posters from this workshop will be considered for a special issue of Advances of Space Research.


Electron Density: D and E Region


Two new D-region options have been introduced with IRI-2001 and now await testing by the user community. The standard IRI D-region model remains in effect as before. A few first comparisons have shown good agreement between the three model options as pointed by Bilitza (USA) in his IRI-2001 overview talk. Pulinets (Russia) pointed out the existence of a large data base of absorption measurements in Russia that could be of help in modeling long-term trends of D-region densities. He will contact the responsible scientists. McKinnell (South Africa) presented a Neural Network (NN) model for E region parameters based on ionosonde data from Grahamstown, South Africa.


The E region in general is well represented by IRI. But some areas of improvement remain: (1) The correct representation of the depth of the nighttime E valley. Incoherent scatter measurements and theoretical studies have shown that the current IRI E-valley is too deep. (2) The enhanced E region ionization due to particle precipitation at auroral latitudes. Bradley (U.K.) reviewed models for sporadic-E as a starting point for the future inclusion of a sporadic-E model in IRI.


Electron Density: F1 Region and F2 Bottomside


IRI-2001 provides considerably improved profiles in this region and includes the F1 probability as a new parameter. These improvements are a result of the annual IRI Task Force Activity that is organized by Radicella (Italy) at the Abdus Salam International Center for Theoretical Physics (ICTP) in Trieste, Italy. Presentations by Reinisch (USA), Mosert (Argentina), Ezquer (Argentina), Adeniyi (Nigeria; presented by Bilitza), and Mahajan (India) discussed these efforts and pointed out areas for future improvements. The IRI group strongly pursues and encourages the establishment of a data base of F1 and bottomside parameters from a large number of globally distributed ionosondes. Especially at high solar activities the current IRI bottomside thickness parameter B0 underestimates Jicamarca incoherent scatter data. The great potential of Jicamarca incoherent scatter data for IRI modelling was reviewed by Chau (Peru). Comparisons of Brazilian rocket data with IRI were presented by Sobral (Brazil) and Muralikrishna (Brazil).


Electron Density: F2 Peak Parameters


With the 2001 version IRI now includes a model for the description of storm effects.  The storm-time updating model of Fuller-Rowell et al. (USA) describes the changes in F2 peak density in terms of the of the 3-hourly ap index (13 values prior to observation time). First comparison with ionosonde and Total Electron Content (TEC) data were presented by Radicella (Italy). The model predicts the observed trends but the study also underlines the importance of the next step in storm effects modeling, namely the description of the

storm-induced changes in the F2 peak height hmF2.


Another prominent feature still missing in the IRI hmF2 model, is the characteristic peak shortly after sunset at equatorial latitudes. With the introduction of the Scherliess-Fejer equatorial ion drift model in IRI-2001, one could now try to include this feature by exploiting the strong correlation between hmF2 and vertical ion drift at the equator especially during nighttime. Obrou (Ivory Coast) and Bilitza (USA) studied this correlation with ionosonde data from Korhogo (Ivory Coast). Batista (Brazil) plans to investigate this aspect further with South American data. The current hmF2 model in IRI is based on the CCIR model for the propagation factor M(3000)F2. Adeniyi (Nigeria) and Bilitza (USA) showed that by using measured values of M(3000)F2, instead of the CCIR model, the evening peak in hmF2 could quite often be reproduced. Their study is based on  ionosonde data from Ougadougou, Burkina Faso, an African station close to the magnetic equator. A better representation of hmF2 during quiet as well as storm time will be an important future goal of the IRI group.


Intercosmos 19 topside sounder data were used to study the equator anomaly region and the longitudinal distribution of F peak and topside parameters (Deminova and Karpachev (Russia). Torres (Chile presented a systematic comparative study of ionosonde data from Brazil and Chile and found in general good agreement between the foF2 and hmF2 measurements and the IRI predictions for low solar activity and discrepancies during high solar activity especially during nighttime. Lazo and Calzadilla (Cuba; presented by Radicella) showed how spherical harmonic analysis can be used for regional foF2 mapping for the European and American sector. Ways to fully access the large amount of ionosonde data stored on microfilm were discussed by Wright (USA)  


Electron Density: Topside, Plasmasphere and TEC


The times and frequency of occurrence of an additional layer (the so-called F3 layer) above the F2 peak were discussed by Batista (Brazil) based on data from ionosondes and topside sounders. Such a layer develops when the equatorial vertical drift pushes the F2 peak upward while simultaneously a new F2 peak develops at lower altitudes due to the standard F layer forming processes. This equatorial phenomenon is most often found during daytime summer and high solar activity. More statistical studies are needed before this feature can be included in IRI.


Shortcomings of the current IRI topside model were discussed by Ezquer (Argentina) based on comparisons with insitu data from the Japanese Taiyo satellite. Efforts to improve the IRI topside model continue with topside sounder data from Alouette and ISIS (Bilitza, USA), and Intercosmos 19 (Pulinets, Russia). Bilitza (USA) proposed a correction factor to better represent the upper topside.  Iwamoto (Japan) discussed ways of correcting the current IRI topside formulas to better represent ISS-b measurements.


Argentine IRI studies with topside and TEC data were discussed by Ezquer Argentina) and Mosert (Argentina). A TEC model for the Brazilian region was compared with IRI and discrepancies were found during sunrise (1-hour shift) and midnight (IRI does not include the observed peak near midnight) (Souza, Brazil). An effort was initiated during the workshop to develop a TEC model for the whole South American continent. The validation of GPS deduced TEC maps from several groups with TOPEX data revealed shortcomings of several of the map algorithms (Orus and Garcia-Fernandez, Spain). An overview of the activities of the International GPS Service (IGS) Ionosphere Working Group was provided by Feltens (Germany; presented by Bilitza). The Barcelona, Spain  UPC group will continue to pursue the updating of IRI with GPS data as a promising way to get better IRI predictions.


Efforts to combine IRI with a plasmaspheric model continue. Gallagher’s GCPM and Chasovitin’s SIM have been proposed as candidate models. Triskova (Czech Republic) pointed out Magion satellite data as potential data source and Oyama (Japan) the Akebono data.


Electron Density: Spread-F and Variability


A model describing the occurrence probability of Spread-F in the American longitude sector was presented by Abdu (Brazil). The model describes the probability in terms of local time, season, solar flux, and latitude (dip=+/- 25). The dominant features of spread-F occurrence in the Indian sector were discussed by Chandra (India) highlighting the strong correlation with solar activity. Combining the Brazilian and Indian efforts should produce a first global spread-F model for IRI. Ezquer (Argentina) reported about first GPS scintillation measurements at Tucuman, Argentina. Iyer (India) compared the scintillation indices (SI, S4) derived from data of the anomaly crest station Rajkot with the models of Aerons and Secan. Wright (USA) discussed the monitoring of Spread-F with digital ionosondes and pointed to the IGY-era “f-plots” as a data source.


Quantitative description of ionopsheric variability  (i.e. standard deviation from a  monthly mean) are now the primary goal of the IRI Taks Force Activity at ICTP. At this workshop first results were presented by Mosert (Argentina) regarding the variability of TEC based on data from two Argentine stations.


Electron and Ion Temperatures


IRI now includes the Truhlik-Triskova-Smilauer model as a new option for the electron temperature. This new model includes the early morning peak in temperature that is currently represented by the standard IRI model only in the F region not in the topside. An important next step is now a correct representation of solar cycle variations. The effect of geomagnetic inclination of electron density and temperature was discussed by Oyama (Japan) based on his Hinotori satellite data. Truhlik (Czech Republic) intends to use the formalism developed for his electron temperature model to also produce a global ion temperature model. Incoherent scatter data could play an important role in improving the IRI plasma temperature models, especially the variation with season and solar activity as was pointed out by Mahajan (India) and Chau (Peru). 


Ion Composition and Drift


Triskova and Truhlik (Czech Republic) presented  a new model for the ion composition (O+, H+, He+, and N+) in the altitude range 500 to 3000 km based on data from Intercosmos 24 (ACTIVE) and from the Atmosphere Explorer satellites. The model describes the ion densities in terms of local time and a specially introduced magnetic field coordinate. The authors plan to also use ion composition data from ISIS 1, ISS-b, AE-B and AEROS to extend their model particularly in terms of the description of solar cycle variations. An effort at the National Space Science Data Center (NSSDC) to make older ionospheric satellite data (like ISIS 1, AEROS and AE) available online was described by Bilitza (USA). Truhlik (Czech Republic) introduced a new model for the light ion density ratio based on ISIS 2, ISS-b, and Intercosmos 24 data. Currently IRI use a constant value of 0.1 for this ratio. It was decided to include the new model in the next version of IRI.


Anderson and Reinisch (USA) pointed to the potential for deducing the daytime electrojet current and vertical ExB ion drift from equatorial magnetometer measurements.  


Applications, New Members, and Future Mettings


A 3-D visualization of the Earth globe with surrounding IRI ionosphere nicely illustrated the great educational capabilities of IRI in conjunction with graphics tools (Watari and Iwamoto, Japan).


Lee-Anne McKinnell (Rhodes University, Grahamstown, South Africa), Vladimir Truhlik (Institute of Atmospheric Physics, Prague, Czech Republic), and V. K. Depuev (IZMIRAN, Moscow, Russia) were elected as new members of the IRI Working Group.


In 2002 there will be a number of meetings with IRI involvement. Most importantly the

next IRI workshop will be held as a session C4.3, entitled "The Path toward Improved Ionosphere Specification and Forecast Models", during the World Space Congress 2002 (34th COSPAR Scientific Assembly) in Houston, Texas (10-19 October, 2002). Session C0.1 (Standard Space Environment Models for ISO) during the same congress will discuss models that are proposed to the International Standardization Organization (ISO) including the IRI model for the ionosphere. During the URSI General Assembly in Maastricht, Netherlands (18-24 August 2002) session G2, entitled "Operational Ionospheric Models Including Data Ingest" is of special interest for the IRI group.


For the 2003 IRI Workshop the IRI Working Group has been presented with two proposals: (1) Rhodes University, Grahamstown, South Africa; (2) Polytechnical University of Catalonia, Barcelona, Spain. The local organizers were tasked with exploring local funding possibilities to support the workshop logistics and maybe also local travel for participants from the region.

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