On the Interaction of Galactic Cosmic Rays with Heliospheric Shocks During Forbush Decreases

Kirin, Anamarija; Vršnak, Bojan; Dumbović, Mateja; Heber, Bernd

doi:10.1007/s11207-020-1593-5

Cited by 4 publications

(4 citation statements)

References 29 publications

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“…Moreover, the graph V(t) reveals a slight depletion before the main rise of V. The graph CR(t) shows the pre-CIR slight increase in CR in more detail (e.g., Lockwood 1971), which is hereafter denoted as "nose". As we show below, the nose is most likely a consequence of the pre-event phase of the decreased V and the steep magnetic field gradient related to the compression caused by the interaction of the fast and slow solar wind (Kirin et al 2020).…”

Section: Cir Structure and The Related Gcr Flux Modulationmentioning

confidence: 82%

“…Because the proposed explanation for this weak increase in GCR flux before the main FD decrease is quite speculative and cannot be fully confirmed by our analysis, we should also consider another possible explanation that is related to the mirror effect at a steep gradient of the magnetic field (including the situation in which a forward shock has already formed) in the region in which the fast solar wind compresses the plasma in the interaction with slow solar wind. In this respect, we note that in the situation in which cylindrical geometry cannot be applied and the adiabatic approximation is not valid, the mirror effect is quite complex and cannot easily be included in the hydrodynamical model such as employed here, that is, the numerical approach has to be applied (see Kirin et al 2020). The results presented by Kirin et al (2020) show that a certain population of particles tends to stay bound to the shock for a certain period of time, indicating that this effect may explain the weak increase in GCR flux before the main FD decrease.…”

Section: Discussionmentioning

confidence: 99%

“…In this respect, we note that in the situation in which cylindrical geometry cannot be applied and the adiabatic approximation is not valid, the mirror effect is quite complex and cannot easily be included in the hydrodynamical model such as employed here, that is, the numerical approach has to be applied (see Kirin et al 2020). The results presented by Kirin et al (2020) show that a certain population of particles tends to stay bound to the shock for a certain period of time, indicating that this effect may explain the weak increase in GCR flux before the main FD decrease. Related to the compression in the frontal parts of CIRs, we also emphasize the so-called snowplow effect (e.g., Guo et al 2021), which is observed as the plasma density increase that starts even before the solar wind speed starts to rise, and which may also cause the GCR pre-CIR increase (Guo et al 2021).…”

Section: Discussionmentioning

confidence: 99%

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Analytic modeling of recurrent Forbush decreases caused by corotating interaction regions

Vršnak

Dumbović

Heber

et al. 2022

A&A

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Context. On scales of days, the galactic cosmic ray (GCR) flux is affected by coronal mass ejections and corotating interaction regions (CIRs), causing so-called Forbush decreases and recurrent Forbush decreases (RFDs), respectively. Aims. We explain the properties and behavior of RFDs recorded at about 1 au that are caused by CIRs generated by solar wind high-speed streams (HSSs) that emanate from coronal holes. Methods. We employed a convection-diffusion GCR propagation model based on the Fokker-Planck equation and applied it to solar wind and interplanetary magnetic field properties at 1 au. Results. Our analysis shows that the only two effects that are relevant for a plausible overall explanation of the observations are the enhanced convection effect caused by the increased velocity of the HSS and the reduced diffusion effect caused by the enhanced magnetic field and its fluctuations within the CIR and HSS structure. These two effects that we considered in the model are sufficient to explain not only the main signatures of RFDs, but also the sometimes observed “over-recovery” and secondary dips in RFD profiles. The explanation in terms of the convection-diffusion GCR propagation hypothesis is tested by applying our model to the observations of a long-lived CIR that recurred over 27 rotations in 2007–2008. Conclusions. Our analysis demonstrates a very good match of the model results and observations.

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Section: Cir Structure and The Related Gcr Flux Modulationmentioning

confidence: 82%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Analytic modeling of recurrent Forbush decreases caused by corotating interaction regions

Vršnak

Dumbović

Heber

et al. 2022

A&A

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“…The mechanisms that affect the modulation of GCRs can be differentiated for the different ICME substructures and physical properties of each region (e.g., Barnden 1973bBarnden , 1973a. The first feature to affect the GCR flux is the ICME shock, which acts as a discontinuity that can reflect particles causing an initial increase in the GCR flux observed just prior to the arrival of some ICMEs and contribute to the initial decrease in GCR flux after the ICME arrival (Cane 2000;Kirin et al 2020). Next, the turbulence of the sheath region acts as a diffusive barrier and affects GCR transport across the region associated with the first decrease in GCR flux (e.g., Wibberenz et al 1997Wibberenz et al , 1998; thus, models often focus on solving the diffusionconvection equation (e.g., Bland 1976;Nishida 1982).…”

Section: Introductionmentioning

confidence: 99%

The Effect of Magnetic Field Line Topology on ICME-related GCR Modulation

Davies,

Scolini,

Winslow

et al. 2023

ApJ

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The large-scale magnetic structure of interplanetary coronal mass ejections (ICMEs) has been shown to affect the galactic cosmic-ray (GCR) flux measured in situ by spacecraft, causing temporary decreases known as Forbush decreases (FDs). In some ICMEs, the magnetic ejecta exhibits a magnetic flux rope (FR) structure; the strong magnetic field strength and closed field line geometry of such ICME FRs have been proposed to act as a shield to GCR transport. In this study, we identify four ICMEs near Earth that drove FDs with similar mean magnetic field strengths (20–25 nT), two ICMEs with more typical mean speeds (∼400 km s−1), and two fast (∼750 km s−1) ICMEs. Within each speed pairing, we identify an ICME that exhibited an open magnetic field line topology and compare its effect on the GCR flux to that which exhibited a mostly closed topology. We investigate the different mechanisms that contribute to the resulting ICME-related FDs and their recovery and determine which properties, if any, play a more important role than others in driving FDs. We find that much of the GCR response to the ICME events in this study is independent of the open or closed magnetic field line topology of the FR and that features such as the fluctuations in speed, magnetic field structure, and expansion within the FR may play more of a role in determining the smaller-scale structure of the FD profile.

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Evolution of Coronal Mass Ejections and the Corresponding Forbush Decreases: Modeling vs. Multi-Spacecraft Observations

et al. 2020

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On the Interaction of Galactic Cosmic Rays with Heliospheric Shocks During Forbush Decreases

Cited by 4 publications

References 29 publications

Analytic modeling of recurrent Forbush decreases caused by corotating interaction regions

Analytic modeling of recurrent Forbush decreases caused by corotating interaction regions

The Effect of Magnetic Field Line Topology on ICME-related GCR Modulation

Evolution of Coronal Mass Ejections and the Corresponding Forbush Decreases: Modeling vs. Multi-Spacecraft Observations

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