Solar Activity Index for the Long-Term Prediction of the F2 Layer Critical Frequency
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Based on a comparison of the 12-month moving averages of the solar activity indices with the ionospheric index of solar activity IG12 for the period of 1954–2014, we estimated the relative accuracies of the solar indices as indicators of solar activity for the medians of the F2 layer critical frequency for a month. These solar indices are the previous (Rz12) and new (Ri12) versions of the relative sunspot number, as well as the 10.7 cm solar radio flux F12 scaled to Rz12, (Rf12) correction for low solar activity. The interval of 1954–2014 spans solar cycles 19–23 and incomplete cycle 24. It was found that, on the whole, the index Ri12 is more accurate than Rz12 and that the indices RF12 and Rf12 are more accurate than Rz12 and Ri12. The accuracies of the indices RF12 and Rf12 for cycles 19–20 coincide. For cycles 21–24, the index Rf12 is more accurate than RF12, and this advantage of Rf12 is especially distinct in cycles 23–24. The index Rf12 differs from RF12 only by the introduction of a new additional correction for low solar activity. This analytical correction was obtained from the condition of the minimum average deviation of Rf12 from IG12, which makes the index Rf12 advantageous as the most adequate indicator of the solar activity for the foF2 median among the solar indices.
The data on the solar activity indices were taken from the websites http://sidc.oma.be/silco (WDC-SILSO, Royal Observatory of Belgium, Brussels) and http://www.ukssdc.ac.uk/wdcc1 (World Data Center for Solar-Terrestrial Physics, Chilton).
The study is supported in part by the Russian Foundation for Basic Research (project no. 17-05-00427) and Program 28 of the Presidium of the Russian Academy of Sciences.
- 5.Bowman, B.R., Tobiska, W.K., Marcos, F.A., Huang, C.Y., Lin, C.S., and Burke, W.J., A new empirical thermospheric density model JB2008 using new solar and geomagnetic indices, in AIAA/AAS Astrodynamics Specialist Conference, AIAA, 2008–6438.Google Scholar
- 8.Clette, F., Cliver, E.W., Lefèvre, L., Svalgaard, L., and Vaquero, J.M., Revision of the sunspot number(s), Space Weather, 2015, vol. 13. https://doi.org/10.1002/2015SW001264
- 12.Gulyaeva, T.L., Modification of the solar activity indices in the International Reference Ionosphere IRI and IRI-Plas models due to recent revision of sunspot number time series, Sol.-Terr. Phys., 2016, vol. 2, no. 3, pp. 87–98.Google Scholar
- 13.Hathaway, D.H., The solar cycle, living rev., Sol. Phys., 2015, vol. 12, no. 4. https://doi.org/10.1007/lrsp-2015-4
- 14.ITU-R. Choice of Indices for Long-Term Ionospheric Predictions, Recommendation ITU-R P.371-8, Geneva: International Telecommunication Union, 1999.Google Scholar
- 15.ITU-R. Reference Ionospheric Characteristics, Recommendation ITU-R P.1239-3, Geneva: International Telecommunication Union, 2012.Google Scholar
- 16.Janardhan, P., Bisoi, S.K., Ananthakrishnan, S., Tokumaru, M., Fujiki, K., Jose, L., and Sridharan, R., A 20 year decline in solar photospheric magnetic fields: Inner-heliospheric signatures and possible implications, J. Geophys. Res.: Space, 2015, vol. 120, pp. 5306–5317. https://doi.org/10.1002/2015JA021123 CrossRefGoogle Scholar
- 17.Jones, W.B. and Gallet, R.M., The representation of diurnal and geographic variations of ionospheric data by numerical methods, ITU Telecommun. J., 1962, vol. 29, pp. 129–147.Google Scholar
- 18.Jones, W.B. and Gallet, R.M., The representation of diurnal and geographic variations of ionospheric data by numerical methods, 2. Control of instability, ITU Telecommun. J., 1965, vol. 32, pp. 18–28.Google Scholar
- 19.Liu, R., Smith, P., and King, J., A new solar index which leads to improved foF2 predictions using the CCIR atlas, Telecommun. J., 1983, vol. 50, no. 8, pp. 408–414.Google Scholar
- 20.Livingston, W., Penn, M.J., and Svalgaard, L., Decreasing sunspot magnetic fields explain unique 10.7 cm radio flux, Astrophys. J. Lett., 2012, vol. 757, id L8. https://doi.org/10.1088/2041-8205/757/1/L8