Spatial coherence of interplanetary coronal mass ejection sheaths at 1 AU

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Ala-Lahti , M , Ruohotie , J , Good , S , Kilpua , E K J & Lugaz , N 2020 , ' Spatial coherence of interplanetary coronal mass ejection sheaths at 1 AU ' , Journal of geophysical research. Space physics , vol. 125 , no. 9 , e2020JA028002 .

Title: Spatial coherence of interplanetary coronal mass ejection sheaths at 1 AU
Author: Ala-Lahti, Matti; Ruohotie, Julia; Good, Simon; Kilpua, Emilia K. J.; Lugaz, Noe
Contributor organization: Particle Physics and Astrophysics
Space Physics Research Group
Department of Physics
Date: 2020-09
Language: eng
Number of pages: 13
Belongs to series: Journal of geophysical research. Space physics
ISSN: 2169-9380
Abstract: The longitudinal spatial coherence near 1 AU of the magnetic field in sheath regions driven by interplanetary coronal mass ejection (ICME) is studied by investigating ACE and Wind spacecraft measurements of 29 sheaths. During 2000-2002 Wind performed prograde orbits, and the non-radial spacecraft separation varied from 0.001 to 0.012 AU between the studied events. We compare the measurements by computing the Pearson correlation coefficients for the magnetic field magnitude and components and estimate the magnetic field coherence by evaluating the scale lengths that give the extrapolated distance of zero correlation between the measurements. The correlation is also separately examined for low- and high-pass filtered data. We discover magnetic fields in ICME sheaths have scale lengths that are larger than those reported in the solar wind but that, in general, are smaller than the ones of the ICME ejecta. Our results imply that magnetic fields in the sheath are more coherently structured and well correlated compared to the solar wind. The largest sheath coherence is reported in the GSE y-direction that has the scale length of 0.149 AU while the lengths for B-x, B-z, and vertical bar B vertical bar vary between 0.024 and 0.035 AU. The same sheath magnitude ordering of scale lengths also apply for the low-pass filtered magnetic field data. We discuss field line draping and the alignment of preexisting discontinuities by the shock passage giving reasoning for the observed results.
Subject: 115 Astronomy, Space science
Peer reviewed: Yes
Usage restriction: openAccess
Self-archived version: acceptedVersion

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