Unprecedented Multipoint Observation of Spatially Varying ICME Turbulence of Different Ages during October 2024 Extreme Solar Storm at 1 AU

TL;DR

This paper presents the first multipoint in situ study of ICME turbulence at 1 AU using four L1 spacecraft separated by approximately $80\,R_E$, enabling azimuthal sampling of sheath and magnetic cloud turbulence. By applying PSD analyses and field-aligned decompositions to high-resolution magnetic-field data from Aditya-L1, Wind, ACE, and DSCOVR, the authors reveal pronounced spatial variability in turbulence maturity, with the sheath showing strong energy injection and the magnetic cloud tending toward a mature Kolmogorov-like cascade, albeit with region-specific deviations. They document pronounced turbulence anisotropy that depends on observing spacecraft and identify signatures of magnetic reconnection and compressible fluctuations in an interaction region between multiple MCs. These results underscore the importance of multipoint measurements for improving space weather forecasting and for understanding how local turbulence processes modulate ICME geoeffectiveness.

Abstract

Understanding turbulence in interplanetary coronal mass ejections is fundamental to space plasma research and critical for assessing the impact of space weather on geospace. Turbulence governs energy cascade, plasma heating, magnetic reconnection, and solar wind magnetosphere coupling, thereby influencing both ICME evolution and geoeffectiveness. While previous event-based and statistical studies have examined ICME turbulence and its radial evolution in great detail, no significant measurements of ICME magnetic turbulence at a specific vantage point have been made using multiple observatories separated azimuthally. Here, we present the first multipoint analysis of MHD turbulence across ICME plasma regions, using four spacecraft at the Sun-Earth L1 point, separated by 80 RE along the dawn-dusk direction. Previous studies reveal that ICME shocks, sheaths, and magnetic clouds are highly non-uniform, with strong azimuthal variability. Using high-resolution magnetic field observations from ISRO's Aditya-L1, NASA's Wind and ACE, and NOAA's DSCOVR, we analyze turbulence associated with the 10th October 2024 solar storm, which triggered the second-strongest geomagnetic storm of solar cycle 25. Our results reveal significant variability and differing turbulence maturity across small separations, supported by analysis of field-aligned and perpendicular magnetic field cascades, indicating strong anisotropies. Sheath turbulence is substantially modified by shock induced energy injection. Evidence of compressible turbulence and plasma energization at the flux rope interaction region indicates that internal processes, such as magnetic reconnection, strongly influence ICME plasma evolution, highlighting pronounced spatial variability in turbulence and plasma states observed by multiple L1 monitors near Earth and underscoring their potential role in space weather impacts.

Figures (10)

• Figure 1: Solar wind and ICME plasma and magnetic field parameters measured by the WIND spacecraft during the extreme solar storm from 10 to 13 October 2024. Panels a-h represent magnetic field magnitude, components in geocentric solar ecliptic coordinates, solar wind bulk speed, ion velocity components along $GSE_{y}$ and $GSE_{z}$, suprathermal pitch angle distribution(432 eV channel), ion density, ion temperature, and ion plasma $\beta$ (the ratio between ion kinetic pressure and magnetic pressure). The Solar wind (SW), ICME sheath (SH), and magnetic cloud (MC) regions are marked above with their corresponding abbreviations. The sheath and magnetic cloud are highlighted in light pink and yellow, respectively. The dip in the magnetic field within MC at 06:00 UT, October 11, is indicated using a red arrow in panel a.
• Figure 2: WSA-ENLIL simulated snapshot of CME in the heliosphere at arrival time at Earth. The solar wind radial velocity is shown in the panels. The complete simulations can be accessed through the URL: https://ccmc.gsfc.nasa.gov/ror/results/viewrun.php?runnumber=Ankush_Bhaskar_122525_SH_1
• Figure 3: Position of Aditya-L1, ACE, DSCOVR, and Wind in GSE (Geocentric Solar Ecliptic) coordinates during the ICME event from October $10^{th}$ to $12^{th}$, 2024
• Figure 4: This figure shows the correlation of total magnetic field and respective components in the GSE coordinate of Wind and Aditya-L1, having the highest separation between them. The left panel displays the uncorrected correlation, whereas the right panel displays the time-lag-corrected correlation.
• Figure 5: The magnetic power spectra of the four spacecraft are displayed in this figure, with panels a to d representing DSCOVR, Aditya-L1, ACE, and Wind, respectively. All magnetic field data have been resampled at 10-second time resolution. The solar wind, sheath, and magnetic cloud can be distinctly identified with their respective turbulence power characteristics.