- The paper finds that the often-neglected EUV late phase of solar flares significantly influences ionospheric total electron content, contributing approximately 30% of the TEC increase seen during the impulsive phase.
- The study leverages high-cadence data from a global network of 956 GNSS stations and SDO measurements to demonstrate the temporal and spatial correlation between coronal emissions and ionospheric responses.
- These results highlight the need to re-evaluate and improve existing ionospheric models like FISM2 to accurately incorporate late-phase effects, which is critical for reliable navigation and communication systems.
The Influence of Different Phases of a Solar Flare on Changes in the Total Electron Content in the Earth's Ionosphere
This paper investigates the nuanced interaction between solar flares and their impacts on the Earth's ionosphere, specifically focusing on changes in the Total Electron Content (TEC) induced by different phases of solar flares. The paper leverages extensive datasets obtained from the Global Navigation Satellite Systems (GNSS) and the Solar Dynamics Observatory (SDO) to address the gaps in our understanding of the ionospheric response to solar event-induced irradiance variations.
The analysis centers on the X2.9 solar flare that occurred on November 3, 2011, with particular attention to its "EUV late phase," a secondary peak in coronal emissions detected by SDO instruments. This late phase, characterized by emissions in the \ion{Fe}{15} 28.4 nm and \ion{Fe}{16} 33.5 nm lines, has not been fully explored in terms of its ionospheric effects. The paper's primary contribution is the assessment of how these emissions contribute to the ionization of the ionospheric layers, resulting in TEC variations, and demonstrating their considerable geoeffective potential despite the overall weaker intensity compared to the impulsive phase.
To achieve this, the authors employ a methodology equipped to capture the dynamic response of TEC using high-cadence (15-second) measurements across a global network of GNSS stations. By analyzing data from 956 stations, the paper outlines statistically significant increases in electron content which coincide temporally with the flares' emissions, thus substantiating the connection between coronal emissions and ionospheric behavior.
Key insights from the paper underscore that the ionospheric response to the EUV late phase accounts for approximately 30% of the TEC increase seen during the solar flare's impulsive phase. This is contrary to prior assessments that largely neglected the late phase contributions. The analysis further reveals not only temporal alignments but also a discernible spatial independence due to the non-uniform GNSS receiver distribution.
From a practical perspective, these findings necessitate a reevaluation of ionospheric modeling approaches to incorporate late-phase effects. This addresses significant implications for global navigation and communication systems which rely on the ionosphere's stability. Moreover, the paper critiques existing spectral models such as FISM2, highlighting their deficiencies in predicting EUV late phase emissions, which could otherwise improve the accuracy of space weather models.
Theoretically, this paper deepens the understanding of solar-terrestrial interactions by illustrating the layered complexity of ionospheric responses to solar events. Future work could expand on these methodologies to include a broader array of flares of varying magnitudes, enhancing the robustness of the current findings and elucidating a more comprehensive view of ionospheric dynamics.
In summary, the paper provides a critical reexamination of solar flare-induced ionospheric disruptions, with a novel focus on the EUV late phase, and sets the stage for further research that could lead to improved predictive capabilities for ionospheric responses to solar activity.