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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/angeo-2019-34
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-2019-34
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 08 Mar 2019

Regular paper | 08 Mar 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Annales Geophysicae (ANGEO).

Long-term trends in the ionospheric response to solar EUV variations

Rajesh Vaishnav1, Christoph Jacobi1, and Jens Berdermann2 Rajesh Vaishnav et al.
  • 1Leipzig Institute for Meteorology, Universität Leipzig, Stephanstr. 3, 04103 Leipzig, Germany
  • 2German Aerospace Center, Kalkhorstweg 53, 17235 Neustrelitz, Germany

Abstract. The thermosphere-ionosphere system shows high complexity due to interaction with the continuously varying solar radiation flux. We investigate the ionospheric response to the temporal and spatial dynamics of the solar activity using 18 years (1999–2017) of total electron content (TEC) maps provided by the international GNSS service (IGS) and twelve solar proxies (F10.7, F1.8, F3.2, F8, F15, F30, He-II, MG-II index, Ly-α, Ca K, DSA and SSN). Cross-wavelet and Lomb Scargle periodogram (LSP) analysis are used to evaluate the different solar proxies in respect to their impact on the global mean TEC (GTEC), which is important for improved ionosphere modelling and forecasts. A 16–32 days period in all the solar proxies and GTEC has been identified. The maximum correlation at this time scale is observed between the He-II, Mg-II, and F30 with respect to GTEC, with an effective time delay of about one day. LSP analysis shows that the most dominant period is 27 days, which is based on mean solar rotation, followed by a 44-day periodicity. In addition, a semi-annual and an annual variation has been observed in GTEC, with the strongest correlation near the equator region where a time delay about 1–2 days exists. The wavelet variance estimation method is used to find the variance in the maximum of the solar cycles (SC) 23 (2000–2002) and 24 (2012–2014), for GTEC and F10.7 index, respectively. Wavelet variance estimation suggests that GTEC variance is highest for the seasonal timescale followed by the 16–32 days period, similar to the F10.7 index highest variance for the 16–32 days period. Variance during SC 23 is larger than during SC 24. The most suitable proxy to represent the solar activity at the time scales of 16–32 days and 32–64 days is He-II. The MG-II index, Ly-α, and F30 may be placed at the second as these indices show the strongest correlation with GTEC, but there are some differences between solar maximum and minimum. The F1.8 and DSA are of limited use to represent the solar impact on GTEC. Empirical orthogonal function (EOF) analysis of the TEC data shows that the first EOF components capture more than 86 % of the variance, and the first three EOF components explain 99 % of the total variance. EOF analysis suggests that the first component is associated with the solar flux.

Rajesh Vaishnav et al.
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Rajesh Vaishnav et al.
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Short summary
We investigate the ionospheric response to the temporal and spatial dynamics of the solar activity using total electron content (TEC) maps and multiple solar proxies. The maximum correlation at 16–32 days time scale is observed between the He-II, Mg-II, and F30 with respect to global mean TEC, with an effective time delay of about one day. The most suitable proxy to represent the solar activity at the time scales of 16–32 days and 32–64 days is He-II.
We investigate the ionospheric response to the temporal and spatial dynamics of the solar...
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