Magnetic clouds along the solar cycle: expansion and magnetic helicity

Dasso, S.; Démoulin, P.; Gulisano, A. M.

doi:10.1017/s1743921312004759

Cited by 10 publications

(10 citation statements)

References 54 publications

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“…The 73 month averages discussed earlier are mostly due to the difference in the maximum phases of the two cycles; cycle-24 rise phase is much weaker than the cycle-23 one (by 54%). Many of these quantities show solar cycle variation, confirming Dasso et al [2012] and Lepping et al [2015] when similar parameters are considered. The parameters (V L , B t , P t , VB z , and B z ) that are directly linked to the solar source show clear solar cycle variation, except for the large modulation caused by periods of extreme activity in the decay phase of cycle 23, viz., October-November 2003 Halloween eruptions [Gopalswamy et al, 2005a] and November 2004 eruptions [Gopalswamy et al, 2006;Echer et al, 2010].…”

Section: Solar Cycle Variationsupporting

confidence: 52%

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Properties and geoeffectiveness of magnetic clouds during solar cycles 23 and 24

et al. 2015

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We report on a study that compares the properties of magnetic clouds (MCs) during the first 73 months of solar cycles 23 and 24 in order to understand the weak geomagnetic activity in cycle 24. We find that the number of MCs did not decline in cycle 24, although the average sunspot number is known to have declined by ~40%. Despite the large number of MCs, their geoeffectiveness in cycle 24 was very low. The average Dst index in the sheath and cloud portions in cycle 24 was −33 nT and −23 nT, compared to −66 nT and −55 nT, respectively, in cycle 23. One of the key outcomes of this investigation is that the reduction in the strength of geomagnetic storms as measured by the Dst index is a direct consequence of the reduction in the factor VBz (the product of the MC speed and the out‐of‐the‐ecliptic component of the MC magnetic field). The reduction in MC‐to‐ambient total pressure in cycle 24 is compensated for by the reduction in the mean MC speed, resulting in the constancy of the dimensionless expansion rate at 1 AU. However, the MC size in cycle 24 was significantly smaller, which can be traced to the anomalous expansion of coronal mass ejections near the Sun reported by Gopalswamy et al. (2014a). One of the consequences of the anomalous expansion seems to be the larger heliocentric distance where the pressure balance between the CME flux ropes and the ambient medium occurs in cycle 24.

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Section: Solar Cycle Variationsupporting

confidence: 52%

“…We also investigate intracycle variations at a slightly finer scale by considering the annual averages of the MC parameters, somewhat similar to Dasso et al . [] and Lepping et al . [], although these authors consider different sets of parameters with some overlap with our parameters.…”

Section: Introductionmentioning

confidence: 99%

Properties and geoeffectiveness of magnetic clouds during solar cycles 23 and 24

et al. 2015

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“…The rise phase of cycle 24 was already interesting because the Sun emerged from a deep solar minimum that gained particular interest among solar-terrestrial scientists (Selhorst et al 2011;Tsurutani et al 2011a;Dasso et al 2012;Gopalswamy et al 2012a;Solomon et al 2013;Lean et al 2014;Potgieter et al 2014). Solar activity is typically represented by the international sunspot number (SSN), but there are many other measures, which are needed for a complete understanding of the solar variability.…”

Section: Methodsmentioning

confidence: 99%

Short-term variability of the Sun-Earth system: an overview of progress made during the CAWSES-II period

Gopalswamy

Tsurutani

Yan

2015

Prog. in Earth and Planet. Sci.

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This paper presents an overview of results obtained during the CAWSES-II period on the short-term variability of the Sun and how it affects the near-Earth space environment. CAWSES-II was planned to examine the behavior of the solar-terrestrial system as the solar activity climbed to its maximum phase in solar cycle 24. After a deep minimum following cycle 23, the Sun climbed to a very weak maximum in terms of the sunspot number in cycle 24 (MiniMax24), so many of the results presented here refer to this weak activity in comparison with cycle 23. The short-term variability that has immediate consequence to Earth and geospace manifests as solar eruptions from closed-field regions and high-speed streams from coronal holes. Both electromagnetic (flares) and mass emissions (coronal mass ejections -CMEs) are involved in solar eruptions, while coronal holes result in high-speed streams that collide with slow wind forming the so-called corotating interaction regions (CIRs). Fast CMEs affect Earth via leading shocks accelerating energetic particles and creating large geomagnetic storms. CIRs and their trailing high-speed streams (HSSs), on the other hand, are responsible for recurrent small geomagnetic storms and extended days of auroral zone activity, respectively. The latter leads to the acceleration of relativistic magnetospheric 'killer' electrons. One of the major consequences of the weak solar activity is the altered physical state of the heliosphere that has serious implications for the shock-driving and storm-causing properties of CMEs. Finally, a discussion is presented on extreme space weather events prompted by the 23 July 2012 super storm event that occurred on the backside of the Sun. Many of these studies were enabled by the simultaneous availability of remote sensing and in situ observations from multiple vantage points with respect to the Sun-Earth line.

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“…Evidences collected over the years show that the solar cycle affects the occurrence of CMEs (e.g., Gopalswamy et al, 2003), with more CMEs during the active period and therefore an expected higher number of detected ICMEs. Previous studies have analyzed the dependence of specific properties of ICMEs and MCs (e.g., size, bulk velocity, or expansion) with the phase of the solar cycle (e.g., Dasso et al, 2012; Jian et al, 2011; Lepping et al, 2011). Furthermore, Hundhausen (1999) found that CMEs emitted during the active period tend to be faster than the ones emitted during the quiet period.…”

Section: Superposed Epochs Of Different Icme Groupsmentioning

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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Magnetic clouds along the solar cycle: expansion and magnetic helicity

Cited by 10 publications

References 54 publications

Properties and geoeffectiveness of magnetic clouds during solar cycles 23 and 24

Properties and geoeffectiveness of magnetic clouds during solar cycles 23 and 24

Short-term variability of the Sun-Earth system: an overview of progress made during the CAWSES-II period

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

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