The High Latitudes in the International Reference Ionosphere (IRI)

COSPAR Scientific Assembly, Hamburg, FRG, July 20-21 1994
Meeting Report / Dieter Bilitza

The 1994 IRI meeting was part of the 30th General Assembly of the Committee on Space Research (COSPAR) that took place in Hamburg, FRG from July 11 to 21. The meeting had 10 well-attended sessions including 9 invited papers, 17 contributed papers, and 10 posters. The sessions titles were: Data for High-Latitude Modeling, Results from Theoretical Models at High Latitudes, Mapping of Ionospheric Characteristics, Storm-time Updating and Indices, D-Region, High-Latitude Plasma Temperatures and Ion composition, IRI Comparisons, Improvements and Usage, Posters, and Final Discussion.

Presentations at this workshop underlined the complex variation patterns and dependencies of ionospheric parameters in the high-latitude ionosphere. It is clear that a different treatment has to be chosen for this part of the globe. Regional mapping, storm-time updating and introduction of auroral boundaries and characteristics are needed to bring IRI closer to real conditions. As a result of the presentations and final discussions the following improvements will be introduced into IRI. [Responsible task members are listed in parentheses]

Auroral oval boundaries:
In his workshop presentation, D. Bilitza (GSFC/HSTX) reviewed the existing models for the description of auroral oval boundaries. Following his recommendation, it was decided to introduce auroral boundaries into IRI in the form of the Holzworth & Meng (1975) parameterization of the Feldstein (1963) auroral ovals using corrected geomagnetic (CGM) coordinates. Magnetic activity is characterised through the 15-min Q index; the correlation between Q and Kp will be explored to help IRI users who prefer the more traditional Kp index. Besides its simplicity, the HMF model has the added advandage that it can be easily updated with measured boundary values where and when available. Auroral boundaries can be also defined through the level of precipitating particle flux. Models based on DMSP (Hardy et al., 1987) and NOAA/TIROS (Fuller-Rowell and Evans, 1987) particle data were also discussed. They could provide the framework for future improvements of IRI. At the present stage the auroral boundary model in IRI will have the primary function of alerting users to the increased variability that can be expected within the auroral oval. [Bilitza; Bradley (U.K) will provide CGM related software]

Polar ionization tongue, ionization hole and patches:
R. Schunk (USU, USA), D. Anderson (AFPL, USA) and D. Rees (UK) reported about their respective modelling efforts at high latitudes and implications for IRI. The high-latitude digisonde database was reviewed by B. Reinisch (ULCAR, USA). D. McEwen (Canada) presented observations of F layer patches and their convection over the polar cap. Schunk suggested that IRI should include mathematical parameterizations of the typical ionization features that are observed (and theoretically modelled) in the high-latitude ionosphere, e.g. the ionization tongue and hole, and the polar patches, even though the actual location, amplitude, and movement of these features are still fare from being predictable at this time. As a first step towards this goal, it was decided to follow a recommendation by D. Anderson and include his Parameterized Ionosphere Model (PIM) as a special high-latitude option in IRI; PIM is a physical-based model that includes the typical high-latitude ionization features; with real-time data input this model becomes part of the Parameterized Real-time Ionosphere Specification Model (PRISM). [Anderson will provide PIM code]

Storm-time updating:
P. Kishcha discussed the analytical updating procedure that was developed by him and his colleagues at IZMIRAN (Moscow, Russia). The algorithm describes the ionospheric effects of magnetic storms and substorms on foF2 and hmf2 based on ionosonde data for 380 storm events. It provides the delta-foF2 and -hmF2 in terms of time since storm onset, AE-index, solar activity, season, local time and geomagnetic latitude. It was decided to include the present version of the IZMIRAN model in IRI to allow storm-time updating at subauroral latitudes. [Kishcha will provide updating code]

The three prime IRI D-region modelling teams reported about their progress and results (A. Danilov, Russia; M. Friedrich, Austria; W. Singer, FRG). As a result of discussions at this meeting two new options will be introduced into IRI. The representation of the mid- and low-latitude D-region electron density in terms of neutral density developed by Friedrich and Tokar (1992) for users who have access to the required neutral densities. With the auroral updating as proposed by Friedrich during this workshop an extension to high-latitudes is possible; the auroral component depends on measured riometer absorption as input parameter. Another new option for mid- and low-latitudes will be the D-region model developed by A. Danilov (Russia) and his colleagues that allows the user to specify conditions of winter anomaly or stratospheric warming. Both models include also a specification of the transition height between molecular and cluster ions which will be useful for the IRI ion composition model. Merging the two D-region rocket data compilation (Friedrich's and Danilov's) into one joint D-region model for IRI is an important future goal of the working teams. [Friedrich and Danilov will provide their model codes]

Presentations about ongoing IRI-related efforts
K. Oyama and his team at ISAS, Japan are continuing their efforts concerning the modeling of the topside plasma temperatures with the help of their OHZORA and AKEBONO in-situ probe data. Oyama presented temperature profiles up to plasmaspheric heights for different high-latitude ranges and times. This group is also working on improved global maps at 600 km. [Oyama]

In two invited talks by K. Schlegel (MPAe, FRG) and P.Collis (EISCAT) the potential of the EISCAT data base for ionospheric modeling and IRI was highlighted. EISCAT data will be the basis for a IRI improvement study in the high-latitude E-region. Initiated by K. Schlegel, this investigation will consider electron density as well as plasma temperatures.[Schlegel]

Work continues on developing a better representation for the half-density point (G-factor) at low latitudes based on digisonde observations, incoherent scatter data, and theoretical results [Reinisch (ULCAR,USA), Mahajan (NPL, India), Anderson (AFPL, USA)]

J. Grebowsky explained the GSFC comprehensive ion mass spectrometer data base (1964-84) that he and his colleagues at Goddard Space Flight Center have compiled. He discussed its potential for scientific studies and for a better representation of the IRI ion composition model in the lower ionosphere. [Grebowsky, Hoegy, Bilitza]

F1-region task force activity at ICTP
During the Final Discussion session a brief report was given about the F1-Region Task Force Activity that took place at the Atmospheric Physics and Radio-propagation Laboratory (APRL) of the International Center for Theoretical Physics (ICTP) in Trieste, Italy in the weeks just preceding the IRI-COSPAR meeting. The APRL Director S. Radicella had invited a dozen scientists (a majority from developing countries) to discus the identification and deduction of F1-region parameters from ionograms and the global mapping of these parameters. The innovative format of bringing together data providers and modelers in front of computer terminals and informal round-table discussions was highly successful and result in several recommendations for improvements of the IRI model and for ionogram data reduction in general. The IRI group strongly endorsed the ICTP/APRL activity and encouraged a continuation and possible expansion of this interesting activity in the coming years.

IRI Meetings, Publications and New Members
The first issue of the IRI Newsletter was published and distributed in June. Contribution and requests should be send to the editor K. Oyama (IRI Vice-chair). Ludmila Triskova from the Institute of Atmospheric Physics in Prague, Czech Republic was elected as new working group member. The papers of the 1992 and 1993 IRI Workshops were published in Advances in Space Research, Volume 14, Number 12 and Volume 15, Number 2, respectively. The next IRI meeting will be held at the National Physical Laboratory in New Dehli, India from January 9 to 13, 1995. It will focus on "Low and Equatorial Latitudes in IRI". The IRI group proposed a 1-day session on "Quantitative Descriptions of Ionospheric Storm Effects" for the 1996 COSPAR meeting in Birmingham, U.K. and jointly with C.2 a 2-day session on "E- and D-Region Physics and Modeling".

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