The radial width of a Coronal Mass Ejection between 0.1 and 0.4 AU estimated from the Heliospheric Imager on STEREO

Savani, N. P.; Rouillard, A. P.; Davies, J. A.; Owens, M. J.; Forsyth, R. J.; Davis, C. J.; Harrison, R. A.

doi:10.5194/angeo-27-4349-2009

Cited by 48 publications

(60 citation statements)

References 57 publications

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“…By assuming our sample is normally distributed, the 95% confidence interval for our aspect ratio estimate is 2.8 ± 0.5. This strongly supports that fast ICMEs are elliptical, and have significantly evolved away from the circular cross section found in the high solar corona and estimated by remote observations from the HI instrument on board STEREO (Savani et al 2009). Figure 5 displays a histogram of the aspect ratio; this figure also displays a Gaussian distribution using the mean and standard deviation calculated earlier.…”

Section: Resultssupporting

confidence: 63%

“…This enables remote observations at distances further away from the Sun, where only in situ measurements had been previously available (e.g., Davis et al 2009;Liu et al 2010aLiu et al , 2010bMostl et al 2009;Rouillard et al 2009Rouillard et al , 2010aRouillard et al , 2010bRouillard et al , 2010c. Therefore, similar to the work by Savani et al (2009Savani et al ( , 2010, the evolving aspect ratio of a single ICME may be investigated over large distances. In the future, it is hoped that these types of detailed studies may substantially reduce this variability caused between events.…”

Section: Discussionmentioning

confidence: 69%

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Evolution of Coronal Mass Ejection Morphology With Increasing Heliocentric Distance. Ii. In Situ Observations

Savani

Owens

Rouillard

et al. 2011

ApJ

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Interplanetary coronal mass ejections (ICMEs) are often observed to travel much faster than the ambient solar wind. If the relative speed between the two exceeds the fast magnetosonic velocity, then a shock wave will form. The Mach number and the shock standoff distance ahead of the ICME leading edge is measured to infer the vertical size of an ICME in a direction that is perpendicular to the solar wind flow. We analyze the shock standoff distance for 45 events varying between 0.5 AU and 5.5 AU in order to infer their physical dimensions. We find that the average ratio of the inferred vertical size to measured radial width, referred to as the aspect ratio, of an ICME is 2.8 ± 0.5. We also compare these results to the geometrical predictions from Paper I that forecast an aspect ratio between 3 and 6. The geometrical solution varies with heliocentric distance and appears to provide a theoretical maximum for the aspect ratio of ICMEs. The minimum aspect ratio appears to remain constant at 1 (i.e., a circular cross section) for all distances. These results suggest that possible distortions to the leading edge of ICMEs are frequent. But, these results may also indicate that the constants calculated in the empirical relationship correlating the different shock front need to be modified; or perhaps both distortions and a change in the empirical formulae are required.

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Section: Resultssupporting

confidence: 63%

Section: Discussionmentioning

confidence: 69%

Evolution of Coronal Mass Ejection Morphology With Increasing Heliocentric Distance. Ii. In Situ Observations

Savani

Owens

Rouillard

et al. 2011

ApJ

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“…Indeed, the self-consistency tests of Lepping et al (1990) only check that the fit to the data provides coherent results with the hypothesis of the model. Evidences of compression in the direction of propagation are present in CME observations (e.g., Savani et al 2009Savani et al , 2010 and in magnetohydrodynamics (MHD) simulations (e.g., Cargill & Schmidt 2002;Odstrcil et al 2004;Manchester et al 2004;Lugaz et al 2005b;Xiong et al 2006). Such a compression flattens the cross section, and such a geometrical feature has been partly taken into account by .…”

Section: Introductionmentioning

confidence: 95%

Does spacecraft trajectory strongly affect detection of magnetic clouds?

Démoulin

Dasso

Janvier

2013

A&A

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Context. Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs). One property of MCs is the presence of a magnetic flux rope. Is the difference between ICMEs with and without MCs intrinsic or rather due to an observational bias? Aims. As the spacecraft has no relationship with the MC trajectory, the frequency distribution of MCs versus the spacecraft distance to the MCs' axis is expected to be approximately flat. However, Lepping & Wu (2010, Ann. Geophys., 28, 1539 confirmed that it is a strongly decreasing function of the estimated impact parameter. Is a flux rope more frequently undetected for larger impact parameter? Methods. In order to answer the questions above, we explore the parameter space of flux rope models, especially the aspect ratio, boundary shape, and current distribution. The proposed models are analyzed as MCs by fitting a circular linear force-free field to the magnetic field computed along simulated crossings. Results. We find that the distribution of the twist within the flux rope and the non-detection due to too low field rotation angle or magnitude only weakly affect the expected frequency distribution of MCs versus impact parameter. However, the estimated impact parameter is increasingly biased to lower values as the flux rope cross section is more elongated orthogonally to the crossing trajectory. The observed distribution of MCs is a natural consequence of a flux rope cross section flattened on average by a factor 2 to 3 depending on the magnetic twist profile. However, the faster MCs at 1 AU, with V > 550 km s −1 , present an almost uniform distribution of MCs vs. impact parameter, which is consistent with round-shaped flux ropes, in contrast with the slower ones. Conclusions. We conclude that the sampling of MCs at various distances from the axis does not significantly affect their detection. The large part of ICMEs without MCs could be due to a too strict criteria for MCs or to the fact that these ICMEs are encountered outside their flux rope or near the leg region, or they do not contain a flux rope.

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“…This expression shows that magnetic energy is reduced in time primarily by the expansion of magnetic flux "rope" often seen at the beginning of a CME (Harrison 1986(Harrison , 1995Harrison et al 1990;Savani et al 2009). As the rope unwinds and rotates, the area increases rapidly with time.…”

Section: Magnetic Storage and Types Of Magnetic Configurationsmentioning

confidence: 99%

A Critical Examination of the Fundamental Assumptions of Solar Flare and Coronal Mass Ejection Models

Spicer

Bingham²,

Harrison

2013

ApJ

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The fundamental assumptions of conventional solar flare and coronal mass ejection (CME) theory are re-examined. In particular, the common theoretical assumption that magnetic energy that drives flares and CMEs can be stored in situ in the corona with sufficient energy density is found wanting. In addition, the observational constraint that flares and CMEs produce non-thermal electrons with fluxes of order 10 34 -10 36 electrons s −1 , with energies of order 10-20 keV, must also be explained. This constraint when imposed on the "standard model" for flares and CMEs is found to miss the mark by many orders of magnitude. We suggest, in conclusion, there are really only two possible ways to explain the requirements of observations and theory: flares and CMEs are caused by mass-loaded prominences or driven directly by emerging magnetized flux.

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The radial width of a Coronal Mass Ejection between 0.1 and 0.4 AU estimated from the Heliospheric Imager on STEREO

Cited by 48 publications

References 57 publications

Evolution of Coronal Mass Ejection Morphology With Increasing Heliocentric Distance. Ii. In Situ Observations

Evolution of Coronal Mass Ejection Morphology With Increasing Heliocentric Distance. Ii. In Situ Observations

Does spacecraft trajectory strongly affect detection of magnetic clouds?

A Critical Examination of the Fundamental Assumptions of Solar Flare and Coronal Mass Ejection Models

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