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

Savani, N. P.; Owens, M. J.; Rouillard, A. P.; Forsyth, R. J.; Kusano, K.; Shiota, Daikou; Kataoka, Ryuho; Jian, L. K.; Bothmer, V.

doi:10.1088/0004-637x/732/2/117

Cited by 37 publications

(49 citation statements)

References 64 publications

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“…For fast ICMEs, shocks can form inside the corona. The region of compressed solar wind bounded by the shock and the ICME leading edge is referred to as the "sheath," and is analogous to the planetary magnetosheaths (though see Siscoe and Odstrčil, 2008;Savani et al, 2011). Magnetic fields in ICME sheaths can frequently be strong enough to trigger geomagnetic activity in their own right , with a quarter (Richardson et al, 2001) to a half (Tsurutani et al, 1988) of all geomagnetic storms potentially attributable to ICME sheaths.…”

Section: Fine-scale Structurementioning

confidence: 99%

The Heliospheric Magnetic Field

Owens

Forsyth

2013

Living Rev. Solar Phys.

222

196

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The heliospheric magnetic field (HMF) is the extension of the coronal magnetic field carried out into the solar system by the solar wind. It is the means by which the Sun interacts with planetary magnetospheres and channels charged particles propagating through the heliosphere. As the HMF remains rooted at the solar photosphere as the Sun rotates, the large-scale HMF traces out an Archimedean spiral. This pattern is distorted by the interaction of fast and slow solar wind streams, as well as the interplanetary manifestations of transient solar eruptions called coronal mass ejections. On the smaller scale, the HMF exhibits an array of waves, discontinuities, and turbulence, which give hints to the solar wind formation process. This review aims to summarise observations and theory of the small-and large-scale structure of the HMF. Solar-cycle and cycle-to-cycle evolution of the HMF is discussed in terms of recent spacecraft observations and pre-spaceage proxies for the HMF in geomagnetic and galactic cosmic ray records.

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Section: Fine-scale Structurementioning

confidence: 99%

The Heliospheric Magnetic Field

Owens

Forsyth

2013

Living Rev. Solar Phys.

222

196

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“…This deformation produces noncircular cross-sections (Riley & Crooker 2004;Owens et al 2006;Owens 2008). Savani et al (2011) obtained a ratio of the transverse width and the radial width of 6. They pointed out that the strongest deformation occurs close to the Sun and the aspect ratio remains roughly constant after overtaking the Venus orbit.…”

Section: Forbush Decreases and MC Propertiesmentioning

confidence: 99%

Energetic-particle-flux decreases related to magnetic cloud passages as observed by the Helios 1 and 2 spacecraft

Blanco

Hidalgo

Gómez-Herrero

et al. 2013

A&A

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It has been observed that a magnetic cloud (MC) can affect the propagation conditions of solar energetic particles and low-energy cosmic rays. This effect is commonly observed as a decrease in the energetic-particle fluxes, which are partially excluded from the interior of the cloud. The twin spacecraft Helios 1 and Helios 2 explored the inner heliosphere between 0.29 AU and 1 AU from the mid 1970s to early 1980s. The E6 Experiment onboard Helios is the energetic-particle detector able to measure electrons, protons and alphas in the range of 300 keV/n to >50 MeV/n. It has been shown previously that, in absence of strong solar-particle events, the single detector rates of the E6 anti-coincidence and saphire Cherenkov detectors are sensitive to cosmic rays with rigidities above GV. Because their statistical precision is in the order of hundreds of counts per second, both detectors are very well suited for studying the short-term decreases observed in their count rates during magnetic cloud passages. A total of 35 magnetic clouds have been identified at the Helios locations. Nineteen of them were free of solar energetic-particle contamination. This subset led us to investigate the effect of magnetic clouds on the galactic cosmic ray (GCR) flux. The depth of the decreases are studied in terms of the solar wind and magnetic field properties of the magnetic cloud. We found dependences with the MC magnetic field strength, magnetic rigidity and with the MC time of flight, with the latter supporting the idea of magnetically closed MCs, i.e. with the two legs rooted in the Sun. We also studied MC properties and found evidence of MC expansion during its journey through the inner heliosphere.

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“…There are evidences both from MHD simulations (Riley et al 2003;Manchester et al 2004) and from observations (Owens et al 2006;Savani et al 2011;Nakwacki et al 2011) that MCs propagating in the interplanetary medium have a trend to develop oblate shapes for their cross sections. This effect is mainly due to the interaction between the MC and the solar wind (Vandas et al 1995;Riley et al 2003).…”

Section: Magnetic Field and Cross Sectionmentioning

confidence: 99%

Magnetic clouds along the solar cycle: expansion and magnetic helicity

Dasso

Démoulin²,

Gulisano³

2011

Proc. IAU

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Abstract. Magnetic clouds (MCs) are objects of extreme importance in the heliosphere. They have a major role on releasing magnetic helicity from the Sun (with crucial consequences on the solar dynamo), they are the hugest transient object in the interplanetary medium, and the main actors for the Sun-Earth coupling. The comparison between models and observations is beginning to clarify several open questions on MCs, such as their internal magnetic configuration and their interaction with the ambient solar wind. Due to the decay of the solar wind pressure with the distance to the Sun, MCs are typically in expansion. However, their detailed and local expansion properties depend on their environment plasma properties. On the other hand, while it is well known that the solar cycle determines several properties of the heliosphere, the effects of the cycle on MC properties are not so well understood. In this work we review two major properties of MCs: (i) their expansion, and (ii) the magnetic flux and helicity that they transport through the interplanetary medium. We find that the amount of magnetic flux and helicity released via MCs during the last solar minimum (years 2007-2009) was significantly lower than in the previous one (years [1995][1996][1997]. Moreover, both MC size and mean velocity are in phase with the solar cycle while the expansion rate is weakly variable and has no relationship with the cycle.

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

Cited by 37 publications

References 64 publications

The Heliospheric Magnetic Field

The Heliospheric Magnetic Field

Energetic-particle-flux decreases related to magnetic cloud passages as observed by the Helios 1 and 2 spacecraft

Magnetic clouds along the solar cycle: expansion and magnetic helicity

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