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Transmission of an ICME Sheath Into the Earth's Magnetosheath and the Occurrence of Traveling Foreshocks.

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Title: Transmission of an ICME Sheath Into the Earth's Magnetosheath and the Occurrence of Traveling Foreshocks.
Authors: Ala‐Lahti, Matti1 matti.ala-lahti@helsinki.fi, Dimmock, Andrew P.2, Pulkkinen, Tuija I.3,4, Good, Simon W.1, Yordanova, Emilya2, Turc, Lucile1, Kilpua, Emilia K. J.1
Source: Journal of Geophysical Research. Space Physics. Dec2021, Vol. 126 Issue 12, p1-21. 21p.
Subject Terms: *Geomagnetism, Interplanetary magnetic fields, Coronal mass ejections, Fluctuations (Physics), Magnetic structure
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. Key Points: Several intervals in an interplanetary coronal mass ejection (ICME) sheath maintained their magnetic structure with transmission into the Earth's magnetosheathThe intervals caused traveling foreshocks, ultralow‐frequency fluctuations, and backstreaming ions upstream of the quasi‐parallel bow shockCorrelation of observations from a solar wind monitor and a spacecraft in the magnetosheath depends on spacecraft alignment [ABSTRACT FROM AUTHOR]
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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. Key Points: Several intervals in an interplanetary coronal mass ejection (ICME) sheath maintained their magnetic structure with transmission into the Earth's magnetosheathThe intervals caused traveling foreshocks, ultralow‐frequency fluctuations, and backstreaming ions upstream of the quasi‐parallel bow shockCorrelation of observations from a solar wind monitor and a spacecraft in the magnetosheath depends on spacecraft alignment [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2021JA029896