The Solar and Geomagnetic Storms in May 2024: A Flash Data Report (2407.07665v2)

Abstract: In May 2024, the scientific community observed intense solar eruptions that resulted in a great geomagnetic storm and auroral extension, highlighting the need to document and quantify these events. This study mainly focuses on their quantification. The source active region (AR 13664) evolved from 113 to 2761 millionths of the solar hemisphere between 4 May and 14 May. AR 13664's magnetic free energy surpassed 10^33 erg on 7 May, triggering 12 X-class flares on 8 -- 15 May. Multiple interplanetary coronal mass ejections (ICMEs) were produced from this AR, accelerating solar energetic particles toward Earth. According to satellite and interplanetary scintillation data, at least 4 ICMEs erupted from 13664 eventually overcoming each other and combining. The shock arrival at 17:05 UT on 10 May significantly compressed the magnetosphere down to ~ 5.04 RE, and triggered a deep Forbush Decrease. GOES satellite data and ground-based neutron monitors confirmed a ground-level enhancement from 2 UT to 10 UT on 11 May 2024. The ICMEs induced exceptional geomagnetic storms, peaking at a Dst index of -412 nT at 2 UT on 11 May, marking the sixth-largest storm since 1957. The AE and AL indices showed great auroral extensions that located the AE/AL stations into the polar cap. We gathered auroral records at that time and reconstructed the equatorward boundary of the visual auroral oval to 29.8{\deg} invariant latitude. We compared naked-eye and camera auroral visibility, providing critical caveats on their difference. We also confirmed global enhancements of storm-enhanced density of the ionosphere.

• The paper details how the evolving AR 13664 triggered multiple X-class flares and sequential ICMEs, leading to a geomagnetic storm with a −412 nT Dst index.
• It employs multi-instrument analysis to uncover significant magnetospheric compression to 5.04 R_E and related cosmic ray variations.
• The study refines space weather predictive models by linking detailed solar eruption data to ionospheric and magnetospheric responses for better risk mitigation.

Overview of Solar and Geomagnetic Storms: May 2024 Events and Implications

Hayakawa et al.'s 2024 paper, published in The Astrophysical Journal, presents a meticulous analysis of the solar and geomagnetic storms that occurred in May 2024. This comprehensive report covers various aspects of these significant space weather events, emphasizing the intensity of the solar eruptions and their profound impacts on Earth's magnetosphere and ionosphere.

Summary and Key Findings

The paper focuses primarily on the solar active region AR 13664, which evolved dramatically between the 4th and 14th of May, undergoing a spatial expansion from 113 to 2761 millionths of the solar hemisphere. On the 7th of May, this region's magnetic free energy exceeded 10^32 erg, subsequently triggering multiple X-class flares, and generating at least four significant interplanetary coronal mass ejections (ICMEs). The compounding effect of these sequential ICMEs resulted in one of the most intense geomagnetic storms in recent history, with the Dst index reaching a nadir of −412 nT on May 11, 2024, ranking as the sixth largest storm since 1957.

Significant Numerical Results and Observations

• Geomagnetic Impact: The storm induced a Dst minimum of −412 nT, placing it among the most intense since official monitoring began. Notably, the AE and AL indices recorded substantial auroral expansions, revealing electric latitudinal extensions down to 29.8° invariant latitude.
• Magnetosphere Compression: Observed significant compression of the magnetosphere, with the boundary contracting to approximately 5.04 R_E, indicative of the substantial pressure exerted by the storm.
• Cosmic Ray Variations: Ground-level enhancements (GLE #74) were detected alongside cosmic ray fluctuations, underscoring the event's impact on atmospheric radiation levels.

Implications for Space Weather Study

The May 2024 solar-terrestrial storm serves as a crucial dataset in understanding geomagnetic disturbances resulting from compounded ICMEs. It not only strengthens empirical models that track ICME interactions, but also enhances the predictability of geomagnetic storm severity, thereby aiding in mitigation strategies for space-weather induced risks to terrestrial and space-borne infrastructure.

Theoretical and Practical Relevance

The paper contributes significantly to solar-terrestrial coupling theories, particularly in the field of understanding how ICME kinematics can lead to extreme geomagnetic storms. The detailed observations of magnetic field dynamics, ionospheric density fluctuations, and auroral phenomena offer insights into the energy transfer mechanisms between solar eruptions and Earth's magnetospheric and ionospheric responses.

Future Directions

Future research should aim at refining models of ICME propagation influenced by pre-existing solar wind conditions and magnetic field configurations. A deeper dive into the interactions among consecutive CMEs using multi-dimensional magnetohydrodynamic (MHD) simulations could offer predictive insights into solar storm interactions and their terrestrial effects. Furthermore, expanding the global network for real-time monitoring of geomagnetic and ionospheric changes can improve predictive capabilities for space weather impacts.

In conclusion, Hayakawa et al.'s 2024 paper presents a meticulously detailed account of a significant solar-terrestrial event, enhancing our understanding of solar storm dynamics and their geomagnetic repercussions. Such studies are invaluable, driving theoretical advancements and practical applications in space weather prediction and management.