Effects of the May 10, 2024 solar storm on the South Atlantic Anomaly: a case study in Bolivia

Abstract We analyzed the strongest geomagnetic storm of the last two decades, which occurred on May 10, 2024, focusing on satellite plasma data, magnetic field variations recorded at the Villa Remedios Magnetic Observatory, and neutron data from the 12-NM64 monitor, both located in La Paz, Bolivia. Situated within the South Atlantic Anomaly (SAA), this region offers a unique perspective on geomagnetic disturbances. The Villa Remedios Observatory recorded a depression of $$-560$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>560</mml:mn> </mml:mrow> </mml:math> nT in the local magnetic field variation ( $$\Delta H_{\text {VR}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:msub> <mml:mi>H</mml:mi> <mml:mtext>VR</mml:mtext> </mml:msub> </mml:mrow> </mml:math> ), a value significantly larger than the minimum of $$-412$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>412</mml:mn> </mml:mrow> </mml:math> nT reported by the global Storm Time Disturbance ( Dst ) index from WDC Kyoto, highlighting pronounced regional variations likely magnified by the influence of the SAA. Concurrently, the neutron monitor at Chacaltaya recorded a Forbush decrease of $$\sim$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>∼</mml:mo> </mml:math> 5% on May 10, followed by a prolonged recovery lasting approximately 13 days. Our observations are consistent with the results from the ALPAQUITA experiment, located on the Chacaltaya mountain plateau, which, in an independent study of this event, detected a modulation of cosmic rays at a median rigidity of $$R_{m} = 76~\textrm{GV}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>R</mml:mi> <mml:mi>m</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>76</mml:mn> <mml:mspace/> <mml:mtext>GV</mml:mtext> </mml:mrow> </mml:math> but observed no significant effect in its sub-TeV channel ( $$R_{m} = 960~\textrm{GV}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>R</mml:mi> <mml:mi>m</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>960</mml:mn> <mml:mspace/> <mml:mtext>GV</mml:mtext> </mml:mrow> </mml:math> ). This provides context for our results, suggesting an upper limit to the energy spectrum of the interplanetary disturbance. Additionally, the ground level enhancement (GLE) event cataloged as GLE74 was examined, revealing its highly anisotropic nature. While polar stations with low rigidity exhibited an intense and early response, our 12-NM64 neutron monitor at Chacaltaya, characterized by its high cutoff rigidity, recorded a markedly attenuated signal. The combined data underscore the complex interaction between solar activity and its terrestrial impacts, demonstrating the critical importance of accounting for the local geomagnetic environment when analyzing such phenomena. Graphical Abstract