In the realm of space weather research, understanding the behavior of interplanetary coronal mass ejections (ICMEs) is crucial for predicting their impact on Earth’s magnetic field and technological infrastructure. Researchers Soumyaranjan Khuntia and Wageesh Mishra, affiliated with the Indian Institute of Technology Bhubaneswar, have delved into the thermal properties of ICMEs and their connection to geoeffectiveness across solar cycles 23-25.
The study, published in the journal “Frontiers in Astronomy and Space Sciences,” presents a comprehensive statistical analysis of magnetic ejecta (MEs) over three solar cycles. The researchers leveraged a polytropic framework to characterize the thermal state of MEs using the event-wise median proton polytropic index (Gamma_p) from in-situ measurements at 1 astronomical unit (AU), the distance between the Earth and the Sun.
Khuntia and Mishra found that MEs are thermodynamically active, rarely evolving adiabatically or isothermally. A significant fraction (45%) of MEs exhibit a heating state, particularly near solar maxima. These heating MEs show strong solar-cycle modulation in Gamma_p, proton temperature, and expansion speed, indicating active in-transit heating processes. In contrast, cooling MEs maintain a nearly constant Gamma_p of 2 across cycles, suggesting enhanced cooling beyond adiabatic expectations and possible thermal energy retention from eruption to 1 AU.
The median Gamma_p value increased from 1.49 in solar cycle 23 to 1.88 in solar cycle 24, indicating a shift to cooling-dominated states over successive cycles. High-impact ICMEs, predominantly heating MEs with a Gamma_p of 0.59, often manifest as magnetic clouds with enhanced magnetic fields, low plasma beta, pronounced sheath compression, elevated expansion, and post-ICME high-speed flows. These characteristics make them the most geoeffective drivers of strong geomagnetic storms.
For the energy sector, understanding the thermal properties and geoeffectiveness of ICMEs is vital for mitigating potential impacts on power grids, satellite operations, and other energy infrastructure. The researchers’ findings establish Gamma_p as a useful diagnostic of ICME thermal states, though a meaningful assessment of geoeffectiveness requires a combined consideration of thermal, plasma, and magnetic field properties. This research contributes to the ongoing efforts to improve space weather forecasting and enhance the resilience of energy systems to solar disturbances.
Source: Khuntia, S., & Mishra, W. (2023). Thermal properties of interplanetary coronal mass ejections at 1 AU and their connection to geoeffectiveness across solar cycles 23-25. Frontiers in Astronomy and Space Sciences, 10, 1-18.
This article is based on research available at arXiv.