Improving the topside electron density model for IRI

We are investigating potential improvements of the IRI topside model using a large data base of topside electron density profiles (more than 100 000 profiles) obtained with the Alouette and ISIS spacecraft from 1965 to 1980. Our modeling approach is based on elements of the older BENT model and of the current IRI topside model. We divide the topside profile into 4 segments reaching up to 3500 km compared to the 3 segments and the upper limit of 1000 km used in the BENT model. Compared to the fixed segment boundaries used in BENT and IRI we use dynamic segment boundaries. In each segment we assume a linearly varying density gradient whereas the BENT model takes a constant gradient. The global and temporal variations of the segment parameters are described in terms of geomagnetic latitude, solar sunspot number and foF2 in a manner similar to the current IRI method. Comparisons with TOPEX total electron data document the dramatic improvements obtained with this new model approach. (C) 1998 COSPAR. Published by Elsevier Science Ltd.