COSPAR – 10 –C4.1: Representation of the Auroral and Polar Ionosphere in IRI

 

A two-day session on the ‘Representation of the Auroral and Polar Ionosphere in the International Reference Ionosphere (IRI)’ was held during the 38th Scientific Assembly of the Committee on Space Research (COSPAR) in Bremen, Germany. IRI is the internationally recommended empirical model for the ionosphere. It is the result of a joint project of COSPAR and the International Union of Radio Science (URSI), and the general assemblies of these two organizations are the main venue for discussions of model performance, shortcomings, improvements, additions, applications and most importantly decisions regarding the next version of the model. These meetings are also the platform for initiating collaborative projects with the goal of future improvements of the model.

 

A total of 42 presentations were given which were grouped into 5 topical areas: IRI at High Latitudes, GNSS Observations and IRI, Representation of the Topside Ionosphere in IRI, Improving the Description of Solar Forcing in IRI, and New Inputs to IRI. A hallmark of IRI sessions is the wide variety of data sources used to check and improve the model. The Bremen meeting was no exception and included presentation that were based on satellite measurements from TIMED, TOPEX, Jason, GPS, COSMIC, CHAMP, Alouette, ISIS, ACTIVE, APEX, CORONOS-I, AE-E, AE-E, and OGO-5, and on ground based measurements from the global network of ionosondes, and on incoherent scatter radar observations from EISCAT, Kharkov, and Arecibo.

 

The majority of presentations were focused on the performance of the IRI model at high latitudes and possible improvements. A first step towards this goal is the introduction of auroral boundaries in the next version of the model, IRI-2010, based on the model developed by Yongliang Zhang and Larry Paxton (JHU/APL, USA) using TIMED-GUVI data. The next step now will be the representation of typical auroral characteristics like the density trough and temperature cusp. Another TIMED instrument, SABER, has provided Chris Mertens (NASA Langley, USA) with the database to develop an auroral E-region storm model which is also scheduled for inclusion in IRI-2010. Several years of continuous EISCAT measurements during the recent deep and extent solar minimum are a unique data source that has not yet been exploited for IRI modeling at high latitudes.

 

One of the most anticipated IRI improvements is the new Neural Network model for the F-peak critical frequency (foF2) and for the propagation factor M(3000)F2 that is related to the F-peak height (hmF2). These models were developed by Lee-Anne McKinnell (HMO, South Africa) and Elija Oyeyemi (University Lagos, Nigeria) based on a large volume of global ionosonde measurements. A presentation during this meeting showed results from a high latitude validation of the new foF2 model and revealed improvements of between 20% and 60% versus the currently used CCIR and URSI foF2 models. This is as a result of new high latitude ionosonde data being made available for inclusion in this model.

 

GPS and COSMIC data are a rich data source for improving the global reliability of the IRI model and several presentations during this meeting reported on data-model comparisons and on new models developed based on these data sources. Bias factors and inherent limitations of tomographic and occultation methods during times of rapid change (sunrise, sunset, storms) and in regions of steep gradients (Equatorial Anomaly region) have to be kept in mind when using these data for global modeling. But GNSS measurements are an excellent data source for the Total Electron Content (TEC) and a number of methods now exists to turn the combined global GNSS measurements (high and low GPS, TOPEX, Jason) into a global mapping of TEC; several methods were discussed during this meeting (Andrzej Krankowski, U Warmia and Marzury, Olsztyn, Poland; Denise Dettmering, German Geodetic Institute, Munich, Germany; Mahdi Alizadeh Elizei, TU Vienna, Austria).

 

A new model for the electron temperature was presented by Vladimir Truhlik (IAP, Prague, Czech Republic). This model was developed with the help of a large database of in situ measurements from many satellites covering more than 2 solar cycles. The significant improvement over the current IRI electron temperature model is the explicit inclusion of variations with solar activity in this new model. It will be included in IRI-2010. Additionally, in IRI-2010 the global representation of the electron and ion density in the region below the F-peak is significantly improved based on the modeling work of David Altadill (Ebro Observatory, Spain) and Phil Richards (GMU, USA) that had been reported at earlier IRI workshops.

 

Presentations from this session will be considered for a special issue of Advances in Space Research. Papers from the previous COSPAR IRI session in Montreal, Canada in 2008 have just been published as Issue 8 in Volume 46 of Advances in Space Research. The term of office for COSPAR officials is limited to 8 years and the current team chairing the  IRI Working Group consisting of Chair, Bodo Reinisch (UML, USA), and his two deputies, Lida Triskova (IAP, Czech Republic; Vice-chair for URSI) and Martin Friedrich (TU Graz, Austria; Vice-chair for COSPAR) had now reached this limit. Therefore election of a new leadership team was an important point on the agenda for the IRI business meeting. A new team was proposed and elected unanimously: Lee-Anne McKinnell (HMO, South Africa; Chair), Shigeto Watanabe (Hokkaido U, Japan; Vice-Chair for COSPAR), Vladmir Truhlik (IAP, Czech Republic; Vice-Chair for URSI). Three new members were elected into the IRI Working Group: Claudia Stolle (National Space Institute, Denmark), Ivan Galkin (UML, USA), and Hanna Rothkaehl (Space Research Center, Poland). The next IRI Workshop is scheduled for 10-14 October 2011 at the Hermanus Magnetic Observatory in Hermanus, South Africa. For the 2013 Workshop the IRI community has been invited to hold its meeting at the University of Warmia and Mazury in Olsztyn, Poland.