On the Cross-Field Diffusion of Galactic Cosmic Rays Into an Icme

Context. Interplanetary coronal mass ejections (ICMEs) are the interplanetary manifestations of solar eruptions. The overtaken solar wind forms a sheath of compressed plasma at the front of ICMEs. Magnetic clouds (MCs) are a subset of ICMEs with specific properties (e.g. the presence of a flux rope). When ICMEs pass near Earth, ground observations indicate that the flux of Galactic cosmic rays (GCRs) decreases. Aims. The main aims of this paper are to find common plasma and magnetic properties of different ICME sub-structures and which ICME properties affect the flux of GCRs near Earth. Methods. We used a superposed epoch method applied to a large set of ICMEs observed in situ by the spacecraft ACE, between 1998 and 2006. We also applied a superposed epoch analysis on GCRs time series observed with the McMurdo neutron monitors. Results. We find that slow MCs at 1 AU have on average more massive sheaths. We conclude that this is because they are more effectively slowed down by drag during their travel from the Sun. Slow MCs also have a more symmetric magnetic field and sheaths expanding similarly as their following MC, while in contrast, fast MCs have an asymmetric magnetic profile and a sheath in compression. In all types of MCs, we find that the proton density and the temperature and the magnetic fluctuations can diffuse within the front of the MC due to 3D reconnection. Finally, we derive a quantitative model that describes the decrease in cosmic rays as a function of the amount of magnetic fluctuations and field strength. Conclusions. The obtained typical profiles of sheath, MC and GCR properties corresponding to slow, middle, and fast ICMEs, can be used for forecasting or modelling these events, and to better understand the transport of energetic particles in ICMEs. They are also useful for improving future operative space weather activities.

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“…This leads to a decrease in the local density of the high energetic particles (e.g. Munakata et al 2006). …”

Section: Model For the N Gcr Typical Profilesmentioning

confidence: 99%

Superposed epoch study of ICME sub-structures near Earth and their effects on Galactic cosmic rays

Masías-Meza

Dasso

Démoulin

et al. 2016

A&A

113

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“…For the cosmic ray density gradient, we used the expanding‐convecting cylinder model of Munakata et al [2006], which is a refinement of the static convecting cylinder model of Kuwabara et al [2004]. Note that an axisymmetric straight cylinder is considered here as a local approximation of the ICME.…”

Section: Expanding Cylinder Model For Cosmic Raysmentioning

confidence: 99%

“…This density gradient depends on the structure of the depleted region, and is calculated from the direction of drift flow and the interplanetary magnetic field (IMF) vector [ Bieber and Evenson , 1998]. The method works by comparing the time variation of the density gradient with that expected on the basis of a theoretical model of the cosmic ray density depleted region [ Munakata et al , 2006]. In this way we can determine the ICME geometry and orientation from the model calculation.…”

Section: Introductionmentioning

confidence: 99%

Determination of interplanetary coronal mass ejection geometry and orientation from ground‐based observations of galactic cosmic rays

et al. 2009

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[1] We have developed a method for determining interplanetary coronal mass ejection (ICME) geometry from galactic cosmic ray data recorded by the ground-based muon detector network. The cosmic ray density depression inside the ICME, which is associated with a Forbush decrease, is represented by an expanding cylinder that is based on a theoretical model of the cosmic ray particle diffusion. ICME geometry and orientation are deduced from observed time variations of cosmic ray density and density gradient and are compared with those deduced from a magnetic flux rope model. From March 2001 to May 2005, 11 ICME events that produced Forbush decreases >2% were observed, and clear variations of the density gradient due to ICME passage were observed in 8 of 11 events. In five of the eight events, signatures of magnetic flux rope structure (large, smooth rotation of magnetic field) were also seen, and the ICME geometry and orientation deduced from the two methods were very similar in three events. This suggests that the cosmic ray-based method can be used as a complementary method for deducing ICME geometry especially for events where a large Forbush decrease is observed.

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“…The neutron-monitor network is a good tool for detecting such anomalies in the pitch angle or longitudinal distribution of CR variations. In recent years, searching for predictors by muon-telescope data has also been developed rather successfully (Munakata et al 2000(Munakata et al , 2005(Munakata et al , 2006Kudela and Storini, 2006). One approach to display the possible precursor effects is the "Ring of Stations" method based on the asymptotic angle distribution of the CR variations which has been used in many studies.…”

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confidence: 99%

Precursor Effects in Different Cases of Forbush Decreases

et al. 2011

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Over the last few years, the pre-decreases or pre-increases of the cosmic-ray intensity observed before a Forbush decrease, called the precursor effect and registered by the worldwide neutron monitor network, have been investigated for different cases of intense events. The Forbush decreases presented in this particular study were chosen from a list of events that occurred in the time period 1967 -2006 and were characterized by an enhanced first harmonic of cosmic-ray anisotropy prior to the interplanetary disturbance arrival. The asymptotic longitudinal cosmic-ray distribution diagrams for the events under consideration were studied using the "Ring of Stations" method, and data on solar flares, solar-wind speed, geomagnetic indices, and interplanetary magnetic field were analyzed in detail. The results revealed that the use of this method allowed the selection of a large number of events with well-defined precursors, which could be separated into at least three categories, according to duration and longitudinal zone. Finally, this analysis showed that the first harmonic of cosmic-ray anisotropy could serve as an adequate tool in the search for precursors and could also be evidence for them.

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On the Cross-Field Diffusion of Galactic Cosmic Rays Into an Icme

Cited by 28 publications

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Superposed epoch study of ICME sub-structures near Earth and their effects on Galactic cosmic rays

Superposed epoch study of ICME sub-structures near Earth and their effects on Galactic cosmic rays

Determination of interplanetary coronal mass ejection geometry and orientation from ground‐based observations of galactic cosmic rays

Precursor Effects in Different Cases of Forbush Decreases

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