Magnetic interaction analysis of multiple interplanetary coronal mass ejections leading to a historic geomagnetic storm in May 2024

TL;DR

The paper addresses why two meso scale ICME counterparts within a complex solar wind produced different geoeffectivity by comparing magnetic content at Wind and STA during the May 2024 storm. It employs Morlet wavelet based spectra to derive magnetic helicity $H_m(k,t)$ and energy $E_m(k,t)$, identifies ejecta cores and reconnection exhausts, and uses HM based solar wind tracking to relate solar sources to spacecraft observations. The key finding is that the STA counterpart had 1.6× higher total magnetic energy and 2.8× higher helicity than the Wind counterpart due to a common origin of the ICMEs and favorable reconnection orientation, whereas the Wind counterpart contained a left handed filament origin ICME with less favorable reconnection. The results show that similar large scale solar wind structures can yield different geoeffectivity based on internal magnetic topology, challenging early predictions and underscoring the need for multi point measurements and physics based modelling of ICME interactions.

Abstract

Interplanetary coronal mass ejections (ICMEs), the large-scale eruptive phenomena capable of shedding a huge amount of solar magnetic helicity and energy are potential in driving strong geomagnetic storms. They complexly evolve while preceded and followed by other large-scale structures e.g. ICMEs. Magnetic interaction among multiple ICMEs may result intense and long-lived geomagnetic storms. Our aim is to understand the reason of substantial changes in the geoeffectivity of two meso-scale separated counterparts of a complex solar wind structure through investigating their magnetic content e.g. helicity, energy and magnetic interaction among multiple ICMEs. We utilized the insitu observations of solar wind from Wind and Solar Terrestrial Relations Observatory-A (STA) spacecraft during the strongest geomagnetic storm period in past two decades on May 10-11, 2024 and heliospheric imagers onboard STA. Our investigation confirms complex interactions among five ICMEs resulting in distinct counterparts within a coalescing large-scale structure. These counterparts possess substantially different magnetic contents. We conclude that the complex counterpart resulted from the interaction among common-origin ICMEs observed by STA, favorably orientated for magnetic reconnection, had 1.6 and 2.8 times higher total magnetic energy and helicity, respectively, than the counterpart containing a left-handed filament-origin ICME observed by Wind. The left-handed ICME non-favorably oriented for magnetic reconnection with the surrounding right-handed, common-origin ICMEs. Therefore, two medium-separated counterparts despite belonging to a common solar wind structure, were potential to lead different geoeffectivity. This ultimately challenges space weather predictions based on early observations.

Figures (4)

• Figure 1: In situ observation during May 10-11, 2024 using (a) MAG, SWE instruments onboard Wind and (b) MAG, SWEA and PLASTIC instruments onboard STA spacecraft. The dotted lines in the $\phi$ panel indicate the nominal sector boundaries of the interplanetary magnetic field derived using a Parker spiral angle obtained from the local solar wind observations at Wind and STA. Here, $\phi$ values between (outside) the lines indicate the magnetic field in the away (toward) sector of the heliosphere. The blue shaded regions $W1$, $W2$, and $S1$ present the localized helicity regions in both time and frequency domains (see Section \ref{['3.1']} for details). The hatched intervals indicate an unperturbed core of ejecta, as discussed in Section \ref{['3.2']}. The 8th (7th) column in panel a (b) shows the energy flux (phase space density) of suprathermal electrons in 265 (247) eV energy bin.
• Figure 2: Trace PSD of magnetic field fluctuation $P_B$ in inertial MHD range and fluctuation amplitude $|\delta \mathbf{B}|/B$ from Wind and STA observations, and transverse velocity components $V_{y,z}$ obtained from Wind observation. The horizontal lines in $V_{y,z}$ panel, indicate $V_{y,z}=50$ Km/s. The hatched regions indicate the intervals of ejecta cores. The black and red vertical lines indicate the shock resulted from the arrival of complex solar wind structures and reconnection exhausts (REs, discussed in Section \ref{['3.3']}), respectively.
• Figure 3: Solar wind magnetic and plasma embedding RE intervals RE1, RE2, and RE3 (in red) observed by MAG, SWE, 3DP instruments onboard Wind (a, b) and MAG, SWEA instruments onboard STA/IMPACT (c), respectively. Note that in a and b, the $V_{L,M,N}$ has been rescaled for clarity.
• Figure 4: Left panel: Elongation angle vs. time for the three tracked structures on May 8-10: Beginning of W1 (blue diamonds), end of W2 (red diamonds) and CME6 leading edge (green diamonds). The black continuous line denotes the best HM fit for the three structures. Predicted arrivals to Earth and fitting residues are presented in the figure. Right panel: The Jmap at a position angle of 90 $^\circ$ for a combination of COR2, HI1 and HI2 on board STEREO-A. Dashed lines represent the mentioned tracked structures: W1, W2 and CME6 on light-blue, red and green, respectively.