A Study of Fluctuations in Magnetic Cloud‐Driven Sheaths

Moissard, Clément; Fontaine, Dominique; Savoini, Philippe

doi:10.1029/2019ja026952

Cited by 26 publications

(30 citation statements)

References 49 publications

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“…Overall sheath compressibility may have been modified be the leading shock; the shock was quasi-parallel at 0.47 au, and quasi-parallel shocks are known to inject compressive fluctuations into the downstream plasma and enhance compressive fluctuation power. Moissard et al (2019), for example, found that sheaths preceded by quasi-parallel shocks tended to have lower power anisotropies and a more equal distribution of power between Alfvénic and compressive fluctuations than sheaths preceded by quasi-perpendicular shocks at 1 au, although this dependence was not strong and based on a relatively small number of quasi-parallel events. Furthermore, large-amplitude compressive fluctuations were clustered near the sheath trailing edge at both spacecraft, suggesting that processes associated with the sheath-ICME boundary also played a role in modifying overall compressibility.…”

Section: Discussionmentioning

confidence: 99%

Radial Evolution of Magnetic Field Fluctuations in an Interplanetary Coronal Mass Ejection Sheath

Good

Ala‐Lahti

Palmerio

et al. 2020

ApJ

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The sheaths of compressed solar wind that precede interplanetary coronal mass ejections (ICMEs) commonly display large-amplitude magnetic field fluctuations. As ICMEs propagate radially from the Sun, the properties of these fluctuations may evolve significantly. We have analyzed magnetic field fluctuations in an ICME sheath observed by MESSENGER at 0.47 au and subsequently by STEREO-B at 1.08 au while the spacecraft were close to radial alignment. Radial changes in fluctuation amplitude, compressibility, inertial-range spectral slope, permutation entropy, Jensen-Shannon complexity, and planar structuring are characterized. These changes are discussed in relation to the evolving turbulent properties of the upstream solar wind, the shock bounding the front of the sheath changing from a quasi-parallel to quasi-perpendicular geometry, and the development of complex structures in the sheath plasma.

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Section: Discussionmentioning

confidence: 99%

Radial Evolution of Magnetic Field Fluctuations in an Interplanetary Coronal Mass Ejection Sheath

Good

Ala‐Lahti

Palmerio

et al. 2020

ApJ

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“…(2019) reported both the vicinity of the shock and ejecta leading edge to be the most geoeffective regions within ICME sheaths, regions that are also associated with high magnetic field magnitudes and fluctuation amplitudes and out‐of‐ecliptic fields. High magnetic field magnitude (Janvier et al., 2019; Kilpua et al., 2019; Owens et al., 2005) and higher power of magnetic fluctuations (Kilpua et al., 2013; Moissard et al., 2019) are also observed to correlate with the speed of the ejecta (Kilpua et al., 2019; Owens et al., 2005).…”

Section: Introductionmentioning

confidence: 99%

Spatial Coherence of Interplanetary Coronal Mass Ejection Sheaths at 1 AU

et al. 2020

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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 |B| 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.

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“…Kilpua et al (2013) and Kilpua et al (2019a) reported an increase in magnetic field fluctuation power with increasing CME speed. Moissard et al (2019) found this same tendency and also emphasised the importance of the magnetic field fluctuation power in the preceding solar wind. Riazantseva et al (2019) analysed high-resolution SPEKTR-R spacecraft magnetic field data for fast and slow solar wind, magnetic clouds and non-cloud ejecta, sheaths and fast-slow stream interaction regions (SIRs; e.g., Richardson, 2018).…”

Section: Introductionmentioning

confidence: 52%

“…Our study highlights that turbulent properties can vary strongly within the sheath and are controlled by various factors, including the properties of the solar wind ahead, e.g. its plasma beta and level of turbulence, the shock strength and configuration, path of the spacecraft through the shock-sheath-ejecta structure, and the properties of the driving CME ejecta, in particular by its speed (Kilpua et al, 2013;Moissard et al, 2019). The variations were in general most drastic for the fastest sheath and most subtle for the slowest sheath in our study.…”

Section: Discussionmentioning

confidence: 94%

“…The shock-sheath transition at MESSENGER had a qualitatively similar 'ageing' effect on the plasma to that seen in the ambient solar wind with radial propagation between the two spacecraft. Moissard et al (2019) performed a statistical investigation of magnetic field fluctuations in 42 CME-driven sheath regions observed in the near-Earth solar wind. In particular, the authors studied compressibility C = P || /(P ⊥ + P || ) and anisotropy A = P ⊥ /(2P || ), where P || and P ⊥ are the parallel and perpendicular power of fluctuations, respectively.…”

Section: Introductionmentioning

confidence: 99%

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Magnetic field fluctuation properties of coronal mass ejection-driven sheath regions in the near-Earth solar wind

Kilpua¹,

Fontaine²,

Good³

et al. 2020

Preprint

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Abstract. In this work, we investigate the magnetic field fluctuations in three coronal mass ejection (CME)-driven sheath regions at 1 AU with their speeds ranging from slow to fast. The data set we use consists primarily of high resolution (0.092 s) magnetic field measurements from the Wind spacecraft. We analyse magnetic field fluctuation amplitudes and fluctuation amplitudes normalised to the mean magnetic field, compressibility, and spectral properties of fluctuations. We also analyse intermittency using various approaches: we apply the partial variance of increments (PVI) method, investigate probability distribution functions of fluctuations, including their skewness and kurtosis, and perform a structure function analysis. Our analysis is conducted separately for three different subregions in the sheath and in the solar wind ahead of it, each 1 hr in duration. We find that, for all cases, the transition from the solar wind ahead to the sheath generates new fluctuations and the intermittency and compressibility increase, while the region closest to the ejecta leading edge resembled the solar wind ahead. The spectral indices exhibit large variability in different parts of the sheath, but are typically steeper than Kolmogorov's in the inertial range. The structure function analysis produced generally much better fit with the extended p-model (Kraichnan's form) than with the standard version, implying that turbulence is not fully developed in CME sheaths near Earth's orbit. The p-values obtained (p~0.8–0.9) also suggest relatively high intermittency. At the smallest timescales investigated, the spectral indices indicate relatively shallow slopes (between −2 and −2.5), suggesting that in CME-driven sheaths at 1 AU the energy cascade from larger to smaller scales could still be ongoing through the ion scale. Regarding many properties (e.g., spectral indices and compressibility) turbulent properties in sheaths, regardless their speed, resemble that of the slow wind, rather fast wind. They are also partly similar to properties reported in terrestrial magnetosheath, in particular regarding their intermittency, compressibility and absence of Kolmogorov's type turbulence. Our study also reveals that turbulent properties can vary considerably within the sheath. This was in particular the case for the fast sheath behind the strong and quasi-parallel shock, including a small, coherent structure embedded close to its midpoint. Our results support the view of the complex formation of the sheath and different physical mechanisms playing a role in generating fluctuations in them.

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A Study of Fluctuations in Magnetic Cloud‐Driven Sheaths

Cited by 26 publications

References 49 publications

Radial Evolution of Magnetic Field Fluctuations in an Interplanetary Coronal Mass Ejection Sheath

Radial Evolution of Magnetic Field Fluctuations in an Interplanetary Coronal Mass Ejection Sheath

Spatial Coherence of Interplanetary Coronal Mass Ejection Sheaths at 1 AU

Magnetic field fluctuation properties of coronal mass ejection-driven sheath regions in the near-Earth solar wind

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