A1 Refereed original research article in a scientific journal
Effect of interplanetary shock waves on turbulence parameters
Authors: Kilpua, Emilia; Good, Simon; Soljento, Juska; Trotta, Domenico; Bäcker, Tia; Ruohotie, Julia; Pomoell, Jens; Sishtla, Chaitanya; Vainio, Rami
Publisher: Copernicus GmbH
Publication year: 2025
Journal:: Annales Geophysicae
Volume: 43
Issue: 2
First page : 489
Last page: 510
ISSN: 0992-7689
eISSN: 1432-0576
DOI: https://doi.org/10.5194/angeo-43-489-2025
Web address : https://doi.org/10.5194/angeo-43-489-2025
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/500346150
Preprint address: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-3564/egusphere-2024-3564.pdf
We perform an extensive statistical investigation of how interplanetary fast forward shocks affect certain turbulence parameters, namely, the normalised cross-helicity, σc; residual energy, σr; and magnetic helicity, σm. A total of 371 shocks detected by Wind at 1 au and 7 shocks by Solar Orbiter at 0.3–0.5 au have been analysed. We explore how the aforementioned turbulence parameters and their variation across the shock depend on the shock characteristics parameterised in terms of the gas compression ratio, upstream plasma beta, velocity jump, and shock angle. In the shock vicinity, fluctuations tend on average to show anti-sunward imbalance (measured as positive σc when rectified to the Parker spiral direction), a dominance of magnetic energy (negative σr) and zero σm, all being typical properties of the solar wind. Anti-sunward imbalance and equipartition (σr∼0) in the upstream is increasingly prevalent with increasing shock velocity jump and decreasing upstream beta and shock angle. Shocks with large velocity jumps and gas compression ratios have considerably more balanced (σc∼0) and more magnetically dominated fluctuations downstream than upstream. From upstream to downstream, we also find that the occurrence of time periods fulfilling strict criteria for Alfvénic fluctuations (AFs) usually decreases, while that of those meeting the criteria for small-scale flux ropes (SFRs) increases. The occurrence of AF-like periods peaks for quasi-parallel shocks with large velocity jumps and small upstream beta values. The occurrence of SFRs increases with an increasing gas compression ratio and upstream beta. The shocks observed by Solar Orbiter below 0.5 au display similar distributions of turbulence parameters and upstream-to-downstream changes to those detected at 1 au. These results are relevant for understanding turbulence and charged-particle acceleration at collisionless shocks.
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Funding information in the publication:
We acknowledge the Finnish Centre of Excellence in Research of Sustainable Space (Research Council of Finland grants 352850 and 352847). Emilia Kilpua acknowledges the ERC under the European Union's Horizon 2020 Research and Innovation Programme Project SolMAG 724391. We also acknowledge funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 101004159 (SERPENTINE). Simon Good is supported by Research Council of Finland grants 338486, 346612, and 359914 (INERTUM). Juska Soljento is supported by the Maili Autio Fund of the Finnish Cultural Foundation grants 00231092 and 00242648.
This research has been supported by the Research Council of Finland (grant nos. 352850, 352847, 338486, and 346612) and the EU H2020 European Research Council (grant no. 101004159).
Open-access funding was provided by the Helsinki University Library.