Transmission of an ICME Sheath Into the Earth's Magnetosheath and the Occurrence of Traveling Foreshocks
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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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Journal of Geophysical Research: Space Physics, Volume 126, issue 12
Abstract
The transmission of a sheath region driven by an interplanetary coronal mass ejection into the Earth's magnetosheath is studied by investigating in situ magnetic field measurements upstream and downstream of the bow shock during an ICME sheath passage on 15 May 2005. We observe three distinct intervals in the immediate upstream region that included a southward magnetic field component and are traveling foreshocks. These traveling foreshocks were observed in the quasi-parallel bow shock that hosted backstreaming ions and magnetic fluctuations at ultralow frequencies. The intervals constituting traveling foreshocks in the upstream survive transmission to the Earth's magnetosheath, where their magnetic field, and particularly the southward component, was significantly amplified. Our results further suggest that the magnetic field fluctuations embedded in an ICME sheath may survive the transmission if their frequency is below ∼0.01 Hz. Although one of the identified intervals was coherent, extending across the ICME sheath and being long-lived, predicting ICME sheath magnetic fields that may transmit to the Earth's magnetosheath from the upstream at L1 observations has ambiguity. This can result from the strong spatial variability of the ICME sheath fields in the longitudinal direction, or alternatively from the ICME sheath fields developing substantially within the short time it takes the plasma to propagate from L1 to the bow shock. This study demonstrates the complex interplay ICME sheaths have with the Earth's magnetosphere when passing by the planet.Description
Funding Information: The authors thank the sources for providing data. M. Ala‐Lahti, E. Kilpua, S. W. Good, and L. Turc acknowledge The Finnish Centre of Excellence in Research of Sustainable Space, funded through the Academy of Finland Grant 312390. M. Ala‐Lahti, E. Kilpua, and S. W. Good also acknowledge Academy of Finland Project 310445 (SMASH). This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement 724391, SolMAG). A. P. Dimmock received financial support from the Swedish National Space Agency (grant 2020‐00111). The work by T. I. Pulkkinen is supported by Academy of Finland grant 310444 and NSF grant 2033563. E. Yordanova research was funded by the Swedish Civil Contingencies Agency (grant 2016‐2021) and SNSA (grant 86/20). The work of L. Turc is supported by the Academy of Finland (grant number 322544) and the University of Helsinki (3‐year research grant 2020‐2022). The authors also wish to thank the two anonymous reviewers, whose constructive comments have lead to a much improved manuscript. Publisher Copyright: © 2021. American Geophysical Union. All Rights Reserved.
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Ala-Lahti, M, Dimmock, A P, Pulkkinen, T I, Good, S W, Yordanova, E, Turc, L & Kilpua, E K J 2021, 'Transmission of an ICME Sheath Into the Earth's Magnetosheath and the Occurrence of Traveling Foreshocks', Journal of Geophysical Research: Space Physics, vol. 126, no. 12, e2021JA029896. https://doi.org/10.1029/2021JA029896