Shaikh, Zubair I;
Verscharen, Daniel;
Vasko, Ivan Y;
Maruca, Bennett A;
(2025)
Temperature anisotropy, instabilities, and thermal processes in low-β plasma.
Astronomy & Astrophysics
10.1051/0004-6361/202555506.
(In press).
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Abstract
Interplanetary coronal mass ejections (ICMEs) are large-scale magnetic structures that influence heliospheric dynamics and space weather. While wave activity has been observed within their low-β (≪ 1) magnetic obstacles, the role of temperature anisotropy and instability remains underexplored. This study examines proton temperature anisotropies, heating, cooling, turbulence, and collisional effects within ICME magnetic obstacles, which are low-β plasmas. Using Wind spacecraft data from 382 ICME magnetic obstacles at 1 au (spanning 1995–2021), we observe that proton temperature and proton β_p follow log-normal distributions. The anisotropy within these regions is primarily constrained to the stable parameter regime below the thresholds for the mirror-mode and oblique firehose instabilities. Additionally, plasmas unstable to proton cyclotron and firehose instabilities exhibit temperatures that are significantly higher -- 50 to 100 times higher than those of stable plasma. Notably, enhanced magnetic fluctuations and low collisional age are observed near instability thresholds, regardless of beta. Although a clear relationship exists between temperature and collisional age, the correlation between turbulent amplitude and collisional age is weak, differing from trends observed in the solar wind. Our results suggest a causal chain whereby high turbulence amplitudes are associated with enhanced heating, linked to reduced collisions, causing increased temperature anisotropy, and ultimately favouring the development of instabilities within ICME magnetic obstacles.
| Type: | Article |
|---|---|
| Title: | Temperature anisotropy, instabilities, and thermal processes in low-β plasma |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1051/0004-6361/202555506 |
| Publisher version: | https://doi.org/10.1051/0004-6361/202555506 |
| Language: | English |
| Additional information: | This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10218429 |
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