Magnetic twist profile inside magnetic clouds derived with a superposed epoch analysis

Lanabere, V.; Masías-Meza, J. J.; Rodriguez, L.; Janvier, Miho; Dasso, S.; Démoulin, P.

doi:10.1051/0004-6361/201937404

Cited by 20 publications

(40 citation statements)

References 49 publications

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“…(25) and (26). We note that all c B values reported in Lanabere et al (2020) are larger by a factor 2. This rescaling does not change any of their conclusions.…”

Section: Distribution Of the Magnetic Asymmetrymentioning

confidence: 62%

“…The asymmetry of the magnetic field intensity in MCs was quantified by Janvier et al (2019) and Lanabere et al (2020). They used the coefficient c B,t , which is defined as…”

Section: Magnetic Asymmetrymentioning

confidence: 99%

“…Such magnetic structures are typically modelled with twisted magnetic flux tubes, or flux ropes (FRs, e.g. Lepping et al 1990;Lynch et al 2003;Dasso 2009;Lanabere et al 2020).…”

Section: Introductionmentioning

confidence: 99%

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Contribution of the ageing effect to the observed asymmetry of interplanetary magnetic clouds

Démoulin

Dasso

Lanabere

et al. 2020

A&A

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Context. Large magnetic structures are launched away from the Sun during solar eruptions. They are observed as (interplanetary) coronal mass ejections (ICMEs or CMEs) with coronal and heliospheric imagers. A fraction of them are observed in situ as magnetic clouds (MCs). Fitting these structures properly with a model requires a better understanding of their evolution. Aims. In situ measurements are made locally when the spacecraft trajectory crosses the magnetic configuration. These observations are taken for different elements of plasma and at different times, and are therefore biased by the expansion of the magnetic configuration. This ageing effect means that stronger magnetic fields are measured at the front than at the rear of MCs. This asymmetry is often present in MC data. However, the question is whether the observed asymmetry can be explained quantitatively from the expansion alone. Methods. Based on self-similar expansion, we derived a method for estimating the expansion rate from the observed plasma velocity. We next corrected the observed magnetic field and the spatial coordinate along the spacecraft trajectory for the ageing effect. This provided corrected data as in the case when the MC internal structure were observed at the same time. Results. We apply the method to 90 best-observed MCs near Earth (1995–2012). The ageing effect is the main source of the observed magnetic asymmetry for only 28% of the MCs. After correcting for the ageing effect, the asymmetry is almost symmetrically distributed between MCs with a stronger magnetic field at the front and those at the rear of MCs. Conclusions. The proposed method can efficiently remove the ageing bias within in situ data of MCs, and more generally, of ICMEs. This allows us to analyse the data with a spatial coordinate, such as in models or remote-sensing observations.

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“…(25) and (26). We note that all c B values reported in Lanabere et al (2020) are larger by a factor 2. This rescaling does not change any of their conclusions.…”

Section: Distribution Of the Magnetic Asymmetrymentioning

confidence: 62%

“…The asymmetry of the magnetic field intensity in MCs was quantified by Janvier et al (2019) and Lanabere et al (2020). They used the coefficient c B,t , which is defined as…”

Section: Magnetic Asymmetrymentioning

confidence: 99%

See 1 more Smart Citation

Contribution of the ageing effect to the observed asymmetry of interplanetary magnetic clouds

Démoulin

Dasso

Lanabere

et al. 2020

A&A

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“…This technique has been used in a variety of cases, in particular in the SW for the investigation of corotating interaction regions (Yermolaev et al, 2015), ICMEs (Janvier et al, 2019), and MCs (Masías-Meza et al, 2016;Rodriguez et al, 2016). A recent study also investigated, using the SEA technique, the profile of the magnetic field twist within MCs (Lanabere et al, 2020). Masías-Meza et al (2016) analyzed how the generic profiles of MCs change depending on their propagation speed.…”

Section: 1029/2020ja028150mentioning

confidence: 99%

20 Years of ACE Data: How Superposed Epoch Analyses Reveal Generic Features in Interplanetary CME Profiles

et al. 2020

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Interplanetary coronal mass ejections (ICMEs) are magnetic structures propagating from the Sun's corona to the interplanetary medium. With over 20 years of observations at the L1 libration point, ACE offers hundreds of ICMEs detected at different times during several solar cycles and with different features such as the propagation speed. We investigate a revisited catalog of more than 400 ICMEs using the superposed epoch method on the mean, median, and the most probable values of the distribution of magnetic and plasma parameters. We also investigate the effects of the speed of ICMEs relative to the solar wind, the solar cycle, and the existence of a magnetic cloud on the generic ICME profile. We find that fast-propagating ICMEs (relatively to the solar wind in front) still show signs of compression at 1 au, as seen by the compressed sheath and the asymmetric profile of the magnetic field. While the solar cycle evolution does not impact the generic features of ICMEs, there are more extreme events during the active part of the cycle, widening the distributions of all parameters. Finally, we find that ICMEs with or without a detected magnetic cloud show similar profiles, which confirms the hypothesis that ICMEs with no detected magnetic clouds are crossed further away from the flux rope core. Such a study provides a generic understanding of processes that shape the overall features of ICMEs in the solar wind and can be extended with future missions at different locations in the solar system. Plain Language Summary Interplanetary coronal mass ejections (ICMEs) are magnetized clouds of solar material expelled from the Sun's atmosphere into the interplanetary medium. In the present article, we use plasma and magnetic data from the NASA ACE mission positioned at the Lagrange 1 point and perform statistical studies over the 400 ICMEs detected over the last 20 years. Such an approach, called a superposed epoch analysis, provides a temporal description of the generic features of ICMEs. In particular, we find that ICMEs that propagate faster than their surrounding solar wind still show compressed regions of plasmas and stronger magnetic field. While we find that the 11-year solar cycle does not affect the generic properties of ICMEs, we observe more extreme events during the active phase. Finally, we also find that a subset of ICMEs, called magnetic clouds and often associated with a stronger and more coherent magnetic field, have the same properties as other ICMEs. This confirms that most ICMEs may be magnetic clouds but which detection is limited by the spacecraft crossing. Such a study, based on long-term heliospheric missions, allows us to probe physical processes that occur during the propagation of ICMEs, which can help better predict space weather and its consequences.

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“…Wang et al (2018) and Zhao et al (2018), on the other hand, found that twist decreases monotonically from the axis to the periphery of FRs using a velocity-modified GH model (Wang et al 2016) that considers dynamic evolution of MCs. In contrast, Lanabere et al (2020) recently applied a superposed epoch analysis to MCs and analyzed their magnetic components in the FR frame, finding that the typical twist distribution of MCs is nearly uniform across the central region and increases moderately (by up to a factor of two) toward the MC periphery.…”

Section: Introductionmentioning

confidence: 99%

Uncovering erosion effects on magnetic flux rope twist

Pal

Kilpua

Good

et al. 2021

A&A

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Context. Magnetic clouds (MCs) are transient structures containing large-scale magnetic flux ropes from solar eruptions. The twist of magnetic field lines around the rope axis reveals information about flux rope formation processes and geoeffectivity. During propagation MC flux ropes may erode via reconnection with the ambient solar wind. Any erosion reduces the magnetic flux and helicity of the ropes, and changes their cross-sectional twist profiles. Aims. This study relates twist profiles in MC flux ropes observed at 1 AU to the amount of erosion undergone by the MCs in interplanetary space. Methods. The twist profiles of two clearly identified MC flux ropes associated with the clear appearance of post eruption arcades in the solar corona are analyzed. To infer the amount of erosion, the magnetic flux content of the ropes in the solar atmosphere is estimated, and compared to estimates at 1 AU. Results. The first MC shows a monotonically decreasing twist from the axis to the periphery, while the second displays high twist at the axis, rising twist near the edges, and lower twist in between. The first MC displays a larger reduction in magnetic flux between the Sun and 1 AU, suggesting more erosion than that seen in the second MC. Conclusions. In the second cloud the rising twist at the rope edges may have been due to an envelope of overlying coronal field lines with relatively high twist, formed by reconnection beneath the erupting flux rope in the low corona. This high-twist envelope remained almost intact from the Sun to 1 AU due to the low erosion levels. In contrast, the high-twist envelope of the first cloud may have been entirely peeled away via erosion by the time it reaches 1 AU.

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Magnetic twist profile inside magnetic clouds derived with a superposed epoch analysis

Cited by 20 publications

References 49 publications

Contribution of the ageing effect to the observed asymmetry of interplanetary magnetic clouds

Contribution of the ageing effect to the observed asymmetry of interplanetary magnetic clouds

20 Years of ACE Data: How Superposed Epoch Analyses Reveal Generic Features in Interplanetary CME Profiles

Uncovering erosion effects on magnetic flux rope twist

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