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Global Electron Content as a New I onospheric Index. Comparison With IRI Modeling Results

Global Electron Content as a New I onospheric Index. Comparison With IRI Modeling Results. Elvira I. Astafieva. Institute of Solar-Terrestrial Physics SD RAS, Irkutsk, Russia. elliada@iszf.irk.ru.

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Global Electron Content as a New I onospheric Index. Comparison With IRI Modeling Results

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  1. Global Electron Content as a New Ionospheric Index. Comparison With IRI Modeling Results Elvira I. Astafieva Institute of Solar-Terrestrial Physics SD RAS, Irkutsk, Russia elliada@iszf.irk.ru

  2. It is known that condition of the Earth’s ionosphere is determined mainly by solar radiation within wide range of wavelengths. A plenty of works have been devoted to study of ionosphere parameters variations depending on solar activity changes. We have proposed a new approach for studying and better understanding of sun-earth connection. It lies in estimation of global electron content (GEC) which is equal to the total number of electrons in the near space environment. An advantage of this approach is in disappearance of local features of ionosphere and in determining of dynamics of global characteristics. Besides, new applications of experimental data are necessary for different ionosphere models correction.

  3. Geodetic Survey Division of Natural Resources Canada (EMRG) [http://www.nrcan­rncan.gc.ca/], Center for Orbit Determination in Europe, University of Berne, Switzerland (CODG) [http://www.cx.unibe.ch/], Jet Propulsion Laboratory of California Institute of Technology (JPLG) [http://www.jpl.nasa.gov/], Grup Universitat Politecnica de Catalunya (UPCG) [http://www.upc.es/], European Space Agency Group (ESAG).

  4. Geodetic Survey Division of Natural Resources Canada (EMRG) [http://www.nrcan­rncan.gc.ca/], Center for Orbit Determination in Europe, University of Berne, Switzerland (CODG) [http://www.cx.unibe.ch/], Jet Propulsion Laboratory of California Institute of Technology (JPLG) [http://www.jpl.nasa.gov/], Grup Universitat Politecnica de Catalunya (UPCG) [http://www.upc.es/], European Space Agency Group (ESAG).

  5. The objectives of this research are to analyze dynamics of global electron content during the 1998-2005 and to compare the dynamics with changes of solar activity and modeled GEC values.

  6. We compared experimental GEC G(t) values with F10.7 as solar activity index F(t), which is equal to solar radiation flux on the wavelength 10.7 cm in s.f.u. units (10-22 Wm-2 Hz-1). We calculated modeled values of GEC M(t) using International Reference Ionosphere 2001. We smoothed G(t), F(t) and M(t) series with the time window τ of 10 days. Diurnal variations appear to be averaged and, therefore, important effects of quick GEC changes cannot be distinguished (such as geomagnetic disturbances).

  7. Modeled GEC (а)- M(t),year 2003hmax= 2000 km, 10000 и 20000 km; (b)–M(t), hmax= 1000 km и 2000 km и G(t). hmax=2000 km

  8. Global Electron Content, 1998-2005

  9. (а) – Experimental GEC; (b) – Solar Radiation Flux F10.7; (c) –Modeled GEC; (d) –G(t), M(t)иF(t);τ = 365 days. G(t) = 0.5 ÷ 3.5 GECU G(t), M(t) and F(t) for all the globe are similar

  10. Regression dependencies N=2771 days (а)-G(t) from M(t); τ = 365 days; (b) - G(t)from F(t); (c) - G(t) from F(t); τ =365 days. G(M)=1.056M + 0.1 G(F)=0.013[F10.7-60] + 0.5

  11. Global Electron Content, Day and Night For understanding of the physical mechanisms and comparison with models it is very important to determine GEC for day Gd and night Gn sides of the Earth as well as their ratio R =  Gd/Gn

  12. A scheme of Estimation of Day and Night GEC H=200 km March 31, 2003 12 UT We carry out calculation of G(t) only for those GIM cells that are located inside or outside the solar terminator border determined for a certain altitude H in the atmosphere.

  13. 1998-2005 (а) – Experimental GEC; (c) –Modeled GEC. GEC of the day and night sides of the Earth for experimental and modeled GEC are similar

  14. A ratio R(t)=Gd/Gnof the day and night sides of the Earth M(t) values for the night side are overestimated as compared to the day side. Maximal values of R(t) correspond to periods of summer and winter solstices.

  15. Seasonal variations of GEC The series of the G(t), M(t) and F(t) were filtered within the period range from 100 to 300 days and normalized on background values of the G(t), M(t) and F(t).

  16. Seasonal variations (b) – Relative amplitudeof GEC variationdG/G,% and dM/M,%; (c) –GECG(t) and F10.7 F(t). GEC is characterized by seasonal variations. Relative amplitude of seasonal variations reaches 10% during low solar activity and it changes up to 30 % during high solar activity.

  17. (а)– relative difference between G(t)and M(t), % during 1998-2005; τ =81 days; (b) –(d) - G(t)и М(t)for the 2001, 2003, 2005. Maximumof GECis related to equinoctial months. Seasonal variations of G(t) and M(t) are not phased.

  18. 27-day variations The series of the G(t) and F(t) were filtered within the period range from 20 to 40 days and normalized on background values of the G(t) and F(t).

  19. 27-day variations, 2003: (а) – dG/G for the globe and of the lighted and darken sides; (b) – dG/GanddF/F; (c) – G(t) for the globe and of the lighted and darken sides; (d) – estimation of the envelope of 27-day variationsG27(t). G(t) lags in time for 2-5 days from F(t).

  20. It is known that response of the ionosphere to ultraviolet radiation flux changes is determined by the lag time and the recombination time constants, which is equal to 1 hour. Founded lag of the 27-day GEC variations relative to corresponding changes of the F10.7 flux can be caused by significantly greater time constants that characterize thermosphere as GEC variations.

  21. 1998 – 2005: (а) – the variations of the 10.7-cm solar radio emission and of sunspot number Rsn; τ= 365 days; (b) – the envelope of 27-day variationsfor F(t) andG(t); τ= 365 days; (c) -the same as for (b), but τ= 81 days; (d) – the solar hydrogen atom emission of Lyman-alpha irradiance at 121.67 nm (L-alpha), τ = 81 days.

  22. CONCLUSION • During the period 1998-2005 the average level of GEC varied from 0.5 to 3.5 GECU. • 27-day variations of GEC are very similar to the ones of the index F10.7. However G(t) lags in time for 2-5 days from F(t). • 3. GEC has seasonal variations with maximum values in equinoctial months. Deep seasonal variations are also typical for a ratio of GEC for the lighted and darken sides of the Earth. Maximal values of this ratio were observed during the periods of summer and winter solstices. • 4. Good agreement between observational and modeled data for GEC was found in general, but there are some distinctions: M(t) values for the night side are overestimated as compared to the day side; IRI 2001 does not take into account rotation of the Sun.

  23. Co-authors: Prof. Edward L. Afraimovich, PhD students Alexey V. Oinatz, Ilya V. Zhivetiev, Yuri V. Yasukevich.

  24. Acknowledgements: We acknowledge academician G.A. Zherebtsov, Drs. V.V. Pipin, V.G. Eselevich, A.V. Mordvinov, L.A. Plyusnina for their support and interest in our work and E.A. Kosogorov for his help in programming. We are grateful to N. Jakowski, D. Bilitza, S.M. Radicella for their interest in our work and good suggestions. We acknowledge for the IONEX data available from the Internet: Geodetic Survey Division of Natural Resources Canada (EMRG), Center for Orbit Determination in Europe, University of Berne, Switzerland (CODG), Jet Propulsion Laboratory of California Institute of Technology (JPLG), Grup Universitat Politecnica de Catalunya (UPCG), European Space Agency Group (ESAG) and others.

  25. The results of this work are accepted for publication in Doklady, Earth Sciences International Reference Ionosphere News

  26. Thank you for your attention! GPS Monitoring WorkGroup, Institute of Solar-Terrestrial Physics, SD RAS, Irkutsk, Russia

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