Earth's Ionospheric Response to Solar Activity

Aurora Borealis over Northern Canada as seen from the International Space Station. Credit: ESA/NASA

Background and Motivation

The Earth’s ionosphere is a dynamic region of the upper atmosphere that is heavily influenced by solar activity. Variations in solar radiation and solar wind can lead to changes in the ionospheric electron density, which in turn affects radio wave propagation and can cause disruptions in communication and navigation systems. This project investigates the variability of global vertical total electron content (VTEC) in response to solar and geomagnetic drivers across three solar cycles (23 to 25). It aims to bridge gaps in understanding how these relationships and their associated time-lags change across distinct solar cycle phases.

Methodology

We compared VTEC data from the Global VTEC maps provided by the Chinese Academy of Sciences (Li et al., 2021) with solar and geomagnetic data from NASA’s OMNIWeb database (King & Papitashvili, 2005). We analyzed the correlations between VTEC and various solar and geomagnetic indices, such as the F10.7 solar flux, sunspot number, and Kp index, across different phases of the solar cycle (rising, maximum, declining, and minimum). We also investigated the time-lags between changes in solar activity and corresponding responses in VTEC to understand the temporal dynamics of these relationships.

Global VTEC average and OMNIWeb solar, geomagnetic, and solar wind parameters from 1998 to 2025.

Key Findings

Our analysis revealed that the correlation between VTEC and solar proxies are strongest and most consistent, primarily during the ascending and descending phases of the solar cycle (Hassan et al., 2026). During solar maximum, the correlations weaken due to disruptions from solar transients, while VTEC becomes more susceptible to non-solar factors during solar minimum. We also observed that geomagnetic indices show moderate correlations and solar wind parameters exhibit weak to no direct global correlation. A characteristic 2-day lag was observed between solar activity and VTEC response, atttributed to thermospheric oxygen dynamics and ionospheric chemistry.

Correlation between VTEC and solar, geomagnetic, and solar wind parameters.

References

Status of CAS global ionospheric maps after the maximum of solar cycle 24
Zishen Li, Ningbo Wang, Ang Liu, Yunbin Yuan, Liang Wang, ...

Satellite Navigation, 2(1), Sep 2021

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Solar wind spatial scales in and comparisons of hourly Wind and ACE plasma and magnetic field data
J. H. Kingand N. E. Papitashvili

Journal of Geophysical Research: Space Physics, 110(A2), Feb 2005

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Investigating Ionospheric TEC Variations in Solar and Geomagnetic Influences Across Solar Activity Phases
Ziyadat Hassan, Zamri Zainal Abidin, Affan Adly Nazri, and Nursyazela Badrina Baharin

Advances in Space Research, Feb 2026

Abstract arXiv BibTeX HTML

This study examines the variability of ionospheric total electron content (VTEC) in response to solar and geomagnetic drivers across solar cycles 23 to 25. While the dominant effect of solar radiation on VTEC is well-known, a comprehensive understanding of how these relationships and their time-lags vary across distinct solar cycle phases and across cycles of differing intensity has been lacking. Using global VTEC data from the Chinese Academy of Sciences Global Ionospheric Maps (CASG) and solar-geophysical indices from NASA’s OMNI dataset spanning from 1998 to 2025, this study bridges that gap by quantifying correlation strengths and time-lag relationships between VTEC and parameters such as \(F_{10.7}\) solar flux, R sunspot number, Kp, Ap, and Dst indices, and solar wind properties. Results show that solar proxies, particularly \(F_{10.7}\) and R sunspot number, exhibit the strongest, most consistent correlations with VTEC, especially during the ascending and descending phases of the solar cycle, with a characteristic \(\sim 2\)-day lag attributed to thermospheric oxygen dynamics and ionospheric recombination processes. In contrast, geomagnetic indices exhibit weaker and phase-dependent correlations, while direct correlations between solar wind parameters and global VTEC are weak, as their influence is primarily mediated by geomagnetic activity and exhibits strong regional and temporal heterogeneity. Phase-resolved analyses further reveal that geomagnetic activity plays a more prominent role during transitional phases, while maximum and minimum periods are dominated by EUV variability and non-solar drivers, respectively. These findings highlight the necessity of incorporating solar phase and time-lag dependencies in ionospheric modelling and forecasting efforts.
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@article{Hassan2026,
  title = {Investigating Ionospheric {TEC} Variations in Solar and Geomagnetic Influences Across Solar Activity Phases},
  issn = {0273-1177},
  url = {http://dx.doi.org/10.1016/j.asr.2026.02.030},
  doi = {10.1016/j.asr.2026.02.030},
  journal = {Advances in Space Research},
  publisher = {Elsevier BV},
  author = {Hassan, Ziyadat and Abidin, Zamri Zainal and Nazri, Affan Adly and Baharin, Nursyazela Badrina},
  year = {2026},
  month = feb,
}
```