Polar Cap TEC Fluctuations due to Solar Wind and Solar Spectral Irradiance Variations During the Peak of the 24th Solar Cycle

This study explores the intricate relationship between spectral irradiance variations and polar cap mean vertical total electron content (MVTEC) climatology, using ground-based GNSS measure-ments from the Thule station in the Arctic. The analysis focuses on understanding how different solar and magnetospheric processes drive changes in MVTEC patterns over a 2-year period. Three primary factors are identified as key drivers of MVTEC variations: (1) Russell-McPherron Effect: During equinoxes, enhanced energy transfer from the solar wind to the magnetosphere, governed by the Russell-McPherron effect, leads to increased MVTEC variability. This phenomenon arises due to the changing orientation of the solar magnetospheric coordinate system relative to the solar equatorial system, which affects the efficiency of energy deposition in the magnetosphere. As a result, higher ionospheric disturbances are observed during these periods, highlighting the sea-sonal influence of geomagnetic activity on polar cap TEC patterns. (2) Solar Irradiance Variations: The study identifies a strong correlation between fluctuations in solar EUV and F10.7, both proxies for solar irradiance, and the 27-day oscillations in MVTEC, especially during the summer months. These periodic variations are closely tied to the rotational behavior of the sun, suggesting a direct link between solar activity and ionospheric dynamics. The findings emphasize how solar spectral irradiance influences the ionization levels in the polar cap region, with implications for under-standing seasonal and short-term changes in the high-latitude ionosphere. (3) E-Layer Conductivity: Seasonal changes in the E-layer's conductivity also play a crucial role in modulating MVTEC variability. During summer, the presence of a conductive E-layer enhances cross-field plasma diffusion, leading to faster plasma decay and reduced MVTEC fluctuations. In contrast, the winter months are characterized by an insulating E-layer, which slows down plasma decay and allows F-layer structures to persist longer, resulting in increased MVTEC variability. This seasonal dis-parity underscores the importance of the E-layer's physical properties in shaping high-latitude ionospheric behavior. The findings of this study underscore the complex interplay between solar wind activity, solar irradiance, and ionospheric dynamics in shaping the observed patterns of polar cap MVTEC. By revealing the combined effects of solar and geomagnetic processes, this research contributes to a more comprehensive understanding of high-latitude ionospheric variability. Further investigation is needed to fully elucidate the mechanisms behind these interactions, particularly in terms of their implications for space weather forecasting and the operation of navigation systems in polar regions. Enhanced models that incorporate these insights can improve the prediction and mitigation of space weather effects on satellite-based technologies and communication systems.