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| Titel |
A Real-Time Assimilative Model for IRI |
| VerfasserIn |
B. W. Reinisch, X. Huang, I. Galkin, D. Bilitza |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250070311
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| Zusammenfassung |
| Ionospheric models are mostly unable to correctly predict the effects of space weather events
and atmospheric disturbances on the ionosphere. This is especially true for the International
Reference Ionosphere (IRI) which by design is a monthly median (climatological) model
[Bilitza et al., 2011]. We propose a Real-Time Assimilative Model “RTAM” for IRI that is
ingesting, initially, the available real-time Digisonde GIRO [Reinisch and Galkin, 2011] data
streams: foF2/hmF2, MUF3000F2, foF1/hmF1, and foE/hmF2 [Galkin et al., 2011].
Deviations of these characteristics, especially foF2, from the monthly median values are the
main cause for errors in the IRI model prediction. The assimilative modeling will provide a
high-resolution, global picture of the ionospheric response to various short-term events
observed during periods of storm activity or the impact of gravity waves coupling the
ionosphere to the lower atmosphere, including timelines of the vertical restructuring of
the plasma distribution. GIRO currently provides reliable real-time data from 42
stations at a cadence of 15 min or 5 min. The number of stations is rapidly growing
and is likely to soon be complemented by satellite borne topside sounders. IRI
uses the characteristics predictions based on CCIR/URSI maps of coefficients. The
diurnal variation of the foF2 characteristic, for example, is presented by the Fourier
series
-6
foF 2(T, Ï,λ,Ï) = a0(Ï,λ,Ï)+ (an(Ï,λ,Ï)cosnT + bn(Ï,λ,Ï)sin nT),
n=1
where T is Universal Time in hours, and Ï, λ, Ï are the geographic latitude, longitude,
and modified dip latitude, respectively. The coefficients an are in turn expanded
as functions Ï, λ, Ï resulting in a set of 24 global maps of 988 coefficients each,
one for each month of the year and for two levels of solar activity, R12=10 and
100, where R12 is the 12-month running-mean of the monthly sunspot number Rm
(2*12*988 = 23,712 coefficients in all) [ITU-R, 2011]. For a given point in time,
988 coefficients need to be adjusted such that the new foF2 map reproduces the
42 values measured at that time by the GIRO network and smoothly transforms
the original model map. This totally underdetermined task has been approached
by using the mathematical tool of Linear Programming; preliminary results are
presented.
The technique can also be applied for regional modeling. Retroactive RTAM
processing of the maps for an entire solar cycle will result in improved CCIR and
URSI maps of the F2 peak characteristics, i.e., in an improved IRI electron density
model.
Bilitza D., L.-A. McKinnell, B. Reinisch, and T. Fuller-Rowell (2011), The International
Reference Ionosphere (IRI) today and in the future, J. Geodesy, 85:909–920, DOI
10.1007/s00190-010-0427-x
Galkin, I. A., B. W. Reinisch, , X. Huang, and D. Bilitza, Assimilation of GIRO data in
Real-Time IRI: Progress Report, International Reference Ionosphere Workshop IRI-2011,
Hermanus, South Africa, October 10-14, 2011.
ITU-R, Information Document on Ionospheric Mapping, Working Party 3L (3L/80 Ann.
4, 3L/86. 3L/95), Oct. 2011.
Reinisch, B. W. and I. A. Galkin (2011), Global Ionospheric Radio Observatory (GIRO),
Earth, Planets and Space, 63(4), 377-381. |
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