ICTP'95 IRI Task Force Activity

The second ICTP task force meeting was held in November 1996 using 
the same innovative meeting format as the first meeting now focussing 
on the modelling of the whole bottomside profile including the F1 
region. Meeting participants included:  S. Radicella (APRL Director, 
Local Organizer), T. Gulyaeva (IZMIRAN, Russia), B. Reinisch (UML,USA), 
R. Leitinger (U. Graz, Austria), J. Titheridge (New Zealand), M. 
Morehead (UK), M. Mosert de Gonzalez (Argentina), J. Adeniyi (Nigeria), 
M.-L. Zhang (ICTP), S.-R. Zhang (P.R. China), B. Zolesi (U. Rome, 
Italy), P. Spalla (U. Firenze, Italy), J. Boska (Czech Rep), G. 
DeFranceschi (U. Rome, Italy) and D. Bilitza (NSSDC, USA; Organizer 
and IRI Chair). 

The specific problems/topics for this meeting were: 1 - Behaviour of Ne 
at fixed heights in the F1 region; 2 - Critical analysis of the IRI F1
parameters; 3 - Study of the F1 layer formation criteria with 
theoretical models; 4 - Comparison of the IRI bottomside profile with
ionogram inversion profiles and with theoretical models; 5 - Validity of 
the two IRI bottomside options. Work and presentation during this 
meeting concluded in the following results/recommendation:

(A) Good progress was made in the effort to improve the F1 region model 
in IRI. In particular the mapping of the frequency/density and dN/dh at 
170 km is well on its way. Using this point will provide some decoupling 
between the F1 region and the bottomside and will also provide a data 
point in the region during the absence of a F1 layer. Ionogram-deduced 
profiles indicate that the variability reaches a minimum in the 150-170 km 
range. There are plans to use Atmosphere Explorer satellite data to study 
the global variation of electron density at 170 km.

(B) Shortcomings of the F1 occurrence model were again discussed. It was 
recommend that rather than providing an cut-off in solar zenith angle a 
probability estimate should be given, e.g., the number of days per month 
for which F1 was observed for the specific solar zenith. This would provide 
a smooth transition from F1 presence (all days) to absence (none of the days).

(C) The IRI bottomside profile depends on a thickness parameter B0 and
a shape parameter B1. Currently B1 is kept constant (=3) in most of the
cases. Presentations showed that better results are obtained if B1 is 
also varied. It is recommended that the IRI profile function be fitted to
measured profiles allowing both parameters to vary and that the global
and diurnal variation of B1 be investigated.

(D) The two IRI options for the bottomside thickness parameter were 
discussed and shortcomings were studied in comparisons with ionosonde
data. Both options are of limited validity at low latitudes since they 
were developed with mid-latitude data. An extension of the h0.5 formula 
(option 2) to low latitudes was presented at the meeting based on Arecibo 
(E) A report about the November 1995 meeting will be published by ICTP.
A continuation of the ICTP Task Force Activity effort is planned for 
August 1996 with a review of the efforts started during the earlier 
meetings and with an extension to the modelling of the topside profile 
in IRI.

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