Inconsistencies Between Local and Global Measures of CME Radial Expansion as Revealed by Spacecraft Conjunctions

Lugaz, Noé; Salman, Tarik M.; Winslow, R. M.; Al-Haddad, Nada; Farrugia, Charles J.; Zhuang, Bin; Galvin, A. B.

doi:10.3847/1538-4357/aba26b

Cited by 34 publications

(72 citation statements)

References 43 publications

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“…Image adapted from Vourlidas et al (2013), copyright by Springer and wide compared to solar cycle 23. Close to the Sun, the CME expansion is driven by the increased magnetic pressure inside the flux rope, while further out they most probably expand due to the decrease of the solar-wind dynamic pressure over distance (Lugaz et al 2020). Therefore, the increased width for CMEs of cycle 24 may be explained by the severe drop ( $ 50%) in the total (magnetic and plasma) heliospheric pressure (see e.g., McComas et al 2013;Gopalswamy et al 2014Gopalswamy et al , 2015Dagnew et al 2020a).…”

Section: General Characteristicsmentioning

confidence: 99%

Space weather: the solar perspective

Temmer

2021

Living Rev Sol Phys

142

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The Sun, as an active star, is the driver of energetic phenomena that structure interplanetary space and affect planetary atmospheres. The effects of Space Weather on Earth and the solar system is of increasing importance as human spaceflight is preparing for lunar and Mars missions. This review is focusing on the solar perspective of the Space Weather relevant phenomena, coronal mass ejections (CMEs), flares, solar energetic particles (SEPs), and solar wind stream interaction regions (SIR). With the advent of the STEREO mission (launched in 2006), literally, new perspectives were provided that enabled for the first time to study coronal structures and the evolution of activity phenomena in three dimensions. New imaging capabilities, covering the entire Sun-Earth distance range, allowed to seamlessly connect CMEs and their interplanetary counterparts measured in-situ (so called ICMEs). This vastly increased our knowledge and understanding of the dynamics of interplanetary space due to solar activity and fostered the development of Space Weather forecasting models. Moreover, we are facing challenging times gathering new data from two extraordinary missions, NASA’s Parker Solar Probe (launched in 2018) and ESA’s Solar Orbiter (launched in 2020), that will in the near future provide more detailed insight into the solar wind evolution and image CMEs from view points never approached before. The current review builds upon the Living Reviews article by Schwenn from 2006, updating on the Space Weather relevant CME-flare-SEP phenomena from the solar perspective, as observed from multiple viewpoints and their concomitant solar surface signatures.

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Section: General Characteristicsmentioning

confidence: 99%

Space weather: the solar perspective

Temmer

2021

Living Rev Sol Phys

142

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“…Another quantity that has been extensively investigated in previous studies is the scaling of the ICME magnetic field with heliocentric distance, which provides information on ICME global expansion (e.g. Démoulin & Dasso 2009;Lugaz et al 2020a). Estimates of the decay of the average magnetic field inside MEs range between −1.30 ± 0.09 and −1.95 ± 0.19 (e.g.…”

Section: Icme Magnetic Field Scaling With Heliocentric Distancementioning

confidence: 99%

“…Good et al 2019), whose properties can be investigated through numerous in situ fitting techniques (e.g. Al-Haddad et al 2013), and neglected non-flux rope configurations, which although more difficult to characterize, are nevertheless frequently observed at 1 au (Nieves-Chinchilla et al 2019) (for a notable exception, see Lugaz et al 2020a). As discussed in the following sections, complex magnetic configurations within ICMEs are in fact often the result of magnetic complexity changes attributable to the interaction of ICMEs with other solar wind structures, while classical FR structures are often a proxy for unperturbed propagation.…”

Section: Introductionmentioning

confidence: 99%

Causes and Consequences of Magnetic Complexity Changes within Interplanetary Coronal Mass Ejections: a Statistical Study

Scolini,

Winslow,

Lugaz

et al. 2021

Preprint

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We present the first statistical analysis of complexity changes affecting the magnetic structure of interplanetary coronal mass ejections (ICMEs), with the aim of answering the questions: How frequently do ICMEs undergo magnetic complexity changes during propagation? What are the causes of such changes? Do the in situ properties of ICMEs differ depending on whether they exhibit complexity changes? We consider multi-spacecraft observations of 31 ICMEs by MESSENGER, Venus Express, ACE, and STEREO between 2008 and 2014 while radially aligned. By analyzing their magnetic properties at the inner and outer spacecraft, we identify complexity changes which manifest as fundamental alterations or significant re-orientations of the ICME. Plasma and suprathermal electron data at 1 au, and simulations of the solar wind enable us to reconstruct the propagation scenario for each event, and to identify critical factors controlling their evolution. Results show that ∼65% of ICMEs change their complexity between Mercury and 1 au and that interaction with multiple large-scale solar wind structures is the driver of these changes. Furthermore, 71% of ICMEs observed at large radial (>0.4 au) but small longitudinal (< 15 • ) separations exhibit complexity changes, indicating that propagation over large distances strongly affects ICMEs. Results also suggest ICMEs may be magnetically coherent over angular scales of at least 15 • , supporting earlier theoretical and observational estimates. This work presents statistical evidence that magnetic complexity changes are consequences of ICME interactions with large-scale solar wind structures, rather than intrinsic to ICME evolution, and that such changes are only partly identifiable from in situ measurements at 1 au.

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“…However, it might not be that simple, since the expansion rate of ICMEs inferred from in situ measurement is not necessarily a good indicator of the global expansion rate of the ICMEs. This was recently demonstrated by Lugaz et al (2020): by studying CMEs observed by spacecraft in conjunction but located at different radial distances from the Sun, they show that the global expansion rate of CMEs (obtained from measurements of multiple spacecraft) is not well correlated with the local measure of the expansion rate (calculated from in situ measurements by a single spacecraft). According to these authors, one scenario that could explain this discrepancy is that CMEs might expand faster close to the Sun (due to internal forces) than at 1 au (where the expansion is more controlled by external forces).…”

Section: Discussion and Physical Interpretationmentioning

confidence: 92%

“…ζ = 0.8), which could explain densities as low as 0.037 cm −3 . It is unfortunately not possible to know when and where the over-expansion of the ejecta started, or even if the expansion rate near the Sun was larger than at 1 au, as found by Lugaz et al (2020), but these simple calculations show that the very low density observed at 1 au on 2002 May 24 and 2002 May 25 could have been caused (completely or partially) by the over-expansion of ICME2.…”

Section: Discussion and Physical Interpretationmentioning

confidence: 94%

Over-expansion of a coronal mass ejection generates sub-Alfvénic plasma conditions in the solar wind at Earth

Chané

Schmieder

Dasso

et al. 2021

A&A

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Context. From May 24–25, 2002, four spacecraft located in the solar wind at about 1 astronomical unit (au) measured plasma densities one to two orders of magnitude lower than usual. The density was so low that the flow became sub-Alfvénic for four hours, and the Alfvén Mach number was as low as 0.4. Consequently, the Earth lost its bow shock, and two long Alfvén wings were generated. Aims. This is one of the lowest density events ever recorded in the solar wind at 1 au, and the least documented one. Our goal is to understand what caused the very low density. Methods. Large Angle and Spectrometric Coronagraph (LASCO) and in situ data were used to identify whether something unusual occurred that could have generated such low densities Results. The very low density was recorded inside a large interplanetary coronal mass ejection (ICME), which displayed a long, linearly declining velocity profile, typical of expanding ICMEs. We deduce a normalised radial expansion rate of 1.6. Such a strong expansion, occurring over a long period of time, implies a radial size expansion growing with the distance from the Sun to the power 1.6. This can explain a two-orders-of-magnitude drop in plasma density. Data from LASCO and the Advanced Composition Explorer show that this over-expanding ICME was travelling in the wake of a previous ICME. Conclusions. The very low densities measured in the solar wind in May 2002 were caused by the over-expansion of a large ICME. This over-expansion was made possible because the ICME was travelling in a low-density and high-velocity environment present in the wake of another ICME coming from a nearby region on the Sun and ejected only three hours previously. Such conditions are very unusual, which explains why such very low densities are almost never observed.

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Inconsistencies Between Local and Global Measures of CME Radial Expansion as Revealed by Spacecraft Conjunctions

Cited by 34 publications

References 43 publications

Space weather: the solar perspective

Space weather: the solar perspective

Causes and Consequences of Magnetic Complexity Changes within Interplanetary Coronal Mass Ejections: a Statistical Study

Over-expansion of a coronal mass ejection generates sub-Alfvénic plasma conditions in the solar wind at Earth

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