ICTP'96 IRI Task Force Activity

Shape of the Bottomside and Topside electron Density Profile

ICTP, 5 August - 23 August 1996

SUMMARY / Dieter Bilitza


The topics of the 1996 IRI Task Force Activity at ICTP were:

(1) Improvement of F1 parameters (foF1, f170, f180) in IRI, 
(2) Improvement of bottomside parameters (B0, B1) in IRI,
(3) Shortcomings of the current IRI topside profile shape
(4) IRI-computed Total Electron Content (TEC) and problem areas,
(5) Results from theoretical models and applications.

Data presented included ionosonde data from many stations worldwide,
incoherent scatter rader data from Arecibo, Puerto Rico and satellite
data from IK 19 (Russia), TOPEX (US/France), AE-C,D,E (USA), GPS and


The most important result was the new probability model for the occurrrence
of an F1 (including L condition) by Radicella and the ICTP group:
	P = (0.5 + 0,5 * cosX )^2.36	X is solar zenith angle
Inclusion of cases with L condition simplified the modelling since
differences due to solar activity and latitude disappear. 

For the f170 and f180 point satellite data show only a small latitudinal
variation but a large variability (two orders of magnitude) at nighttime.
A first attempt was made to represent f170 in terms of M300 and foF2.

RECOMMENDATION FOR IRI: Inclusion of the new probabilty function to
provide users with an estimate of how likely s/he would encounter an
F1 feature. The foF1 Ducharme et al. formula should now be used with
the new occurrence criteria of P=0.5.

FUTURE TASK: Establish an f170 model in terms of solar zenith angle,
latitude, solar sunspot number and season [Task team: Radicella and his
ICTP team; Bilitza will provide his satellite data compilation]; During
nighttime satellite data should be compared with incoherent scatter data 
to establish a better representation of the upper nighttime valley
region [Mahajan, Bilitza].  


Comparisons of B0 and B1 parameters obtained with the UML Artiste
program, the POLAN program and from a theoretical model showed good
agreement. Combining these data new B0 parameters were established for
daytime winter and summer for high and low solar activity. The high
solar activity case still requires data near the magnetic equator.

RECOMMENDATION FOR IRI: New B0 parameters can be included for the B0
table option for daytime summer and winter conditions; a special option
for the inclusion of variable B1 based on the Jicamarca digisonde data 

FUTURE TASK: Establish global plots of B0 parameters for nighttime
and for B1 for daytime and nighttime [Radicella and Mosert]. Analytical
formulas to describe the diurnal varaition of B0 and B1.


Inclusion of the new F1 and bottomside parameters in an IRI profile
representation were discussed and the necessary constraints were
established: (1) the point where the bottomside profile becomes
independent of B1 {if this point is below foF1 a higher point has to be
chosen}; (2) the derivative at that point; (3) a minimum in the gradient
at foF1; (3) the f170 point; (4) the valley-top; (5) the gradient at
the valley-top; the last two constraints could be satisfied by a
seperate (parabolic) merging function.

FUTURE TASK: Find a functional representation for the intermediate
and F1 region that will be able to fullfill the various constraints
[Reinisch and his UML team]. 


The major shortcomings of the current representation of the topside profile 
shape in IRI are the following:

(1) At high latitudes and high solar activity the topside gradient
becomes close to 0 and can even become positive.

(2) Comparisons with incoherent scatter data and topside sounder data 
during this meeting showed that IRI consitently overestimates the 
mid-latitude measurements, especially during nighttime.

(3) Close to the magnetic equator comparisons have shown that IRI 
underestimates considerably the topside densities during high solar 

FUTURE TASK: Ways of improving the current IRI topside profile parameters
have to be investigated [Bilitza]; New modelling approachs should be
continued specifically in terms of a better coordinate system and 
a reduced number of topside parameters [Leitinger, Titheridge]; The
global and altitudinal variation of the topside scale-height should be
established from topside sounder data [Pulinets] 

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