xxth GENERAL ASSEMBLY OF IUGG VIENNA (AUSTRIA)

IAGA NEWS N0.29
further evaluate the latitudinal influence as well as
variations with solar and magnetic activity. D Anderson showed
that his theoretically-derived profiles could be helpful for
this purpose.
Concerning the F2-peak, there exists growing interest in
regional foF2 maps, in particular for the polar caps. Thiemann
et al presented an interesting study using Dvinskikh's
empirical orthognal functions. This subject will be considered
in more detail in forthcoming group meetings. For hmF2, the
group has been strongly promoting direct mapping of measured
hmF2 values; up to now, predictions are obtained from global
maps for the propagation factor M ( 3000) F2. With only a few
incoherent scatter stations worldwide, the main data input
must come from true-height analysis of ionograms.
1.3 Topside ionosphere: K Rawer has shown that a better
representation may be possible by using field-aligned
parameters. Topside sounder data, in particular those from
recent Japanese and Soviet satellites, are crucial for this
task. It is hoped that these data will be made accessible to
the IRI group.
2 • PLASMA TEMPERATURES
Seasonal trends and changes with solar and magnetic activity
need further investigation, preferable with a combined data
base of staellite and incoherent scatter data. K Oyama
reviewed the wealth of temperature data collected by several
Japanese satellites over the past two decades. This data base
may lead to considerable improvements of the IRI Models.
Effects of regional heating, in particular in the auroral
zones, should be considered. The moving boundary of these
zones presents, however, a serious problem. EISCAT and
Sonderstrom data might help to assess these temperature
features.
3. ION COMPOSITION
IRI-90 includes as a new option the Danilov-Yaichnikov model.
At this meeting, first comparisons were presented between the
D-Y model and a large data base of satellite ion mass
spectrometer measurements compiled by W Hoegy et al. This
continuing effort could result in important improvements to
the IRI Model. D Bilitza introduced a promising new modelling
scheme in which the transition heights play a major role. His
analysis indicated, however, major discrepancies between the
transition heights deduced from different models. Incoherent
scatter and satellite data should be compared to resolve these
differences. Further work is planned concerning the
description of D-region cluster ions in IRI. The transition
height from molecular to cluster ions was felt to be a
critical parameter.
4. ION DRIFT
The preliminary IRI-90 ion drift model (written in PASCAL) is
available from E Kazmirovsky. His Fourier description was
established with ground-based radio observations. It was
suggested that A Richmond's model, which is based on
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