Heliospheric modulation of cosmic rays in solar cycles 19–23

Krymsky, G. F.; Krivoshapkin, P. A.; Gerasimova, S. K.; Gololobov, P. Yu.; Григорьев, В. Г.; Starodubtsev, S. A.

doi:10.1134/s106377371208004x

Cited by 8 publications

(5 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The tilt angle of the wavy HCS, on the other hand, had not decreased as rapidly as the magnitude of the HMF at Earth during this period, but eventually also reached a minimum value at the end of 2009. Ahluwalia and Ygbuhay (2011), Stozhkov et al (2009), Mewaldt et al (2010 and Krymsky et al (2012) all reported that CRs with high rigidity reached record setting intensities during this time (see also Heber et al, 2009;McDonald et al, 2010). It followed from observations for this period that the delay between the time for minimum sunspot numbers and maximum CR intensities was at least three times longer than during previous even numbered solar cycles (e.g., Kane, 2011).…”

Section: The Unusual Solar Minimum Of 2007 -2009mentioning

confidence: 83%

“…When protons drift inwards mainly through the equatorial regions of the heliosphere (A < 0 polarity cycles) they encounter the dynamic HCS and get progressively reduced by its increasing waviness as solar activity surges. This produces the sharp peaks in the galactic CR intensity-time profiles whereas during the A > 0 cycles the profiles are generally flatter (for recent updates see, e.g., Potgieter, 2011;Krymsky et al, 2012;Potgieter, 2013). The effect reverses for negatively charged galactic CRs causing charge-sign dependent effects as reviewed by, e.g., Heber andPotgieter (2006, 2008) and Kóta (2012).…”

Section: Gradient Curvature and Current Sheet Driftsmentioning

confidence: 98%

See 1 more Smart Citation

Solar Modulation of Cosmic Rays

Potgieter

2013

Living Rev. Solar Phys.

480

377

View full text Add to dashboard Cite

This is an overview of the solar modulation of cosmic rays in the heliosphere. It is a broad topic with numerous intriguing aspects so that a research framework has to be chosen to concentrate on. The review focuses on the basic paradigms and departure points without presenting advanced theoretical or observational details for which there exists a large number of comprehensive reviews. Instead, emphasis is placed on numerical modeling which has played an increasingly significant role as computational resources have become more abundant. A main theme is the progress that has been made over the years. The emphasis is on the global features of CR modulation and on the causes of the observed 11-year and 22-year cycles and charge-sign dependent modulation. Illustrative examples of some of the theoretical and observational milestones are presented, without attempting to review all details or every contribution made in this field of research. Controversial aspects are discussed where appropriate, with accompanying challenges and future prospects. The year 2012 was the centennial celebration of the discovery of cosmic rays so that several general reviews were dedicated to historical aspects so that such developments are briefly presented only in a few cases.

show abstract

Section: The Unusual Solar Minimum Of 2007 -2009mentioning

confidence: 83%

Section: Gradient Curvature and Current Sheet Driftsmentioning

confidence: 98%

Solar Modulation of Cosmic Rays

Potgieter

2013

Living Rev. Solar Phys.

480

377

View full text Add to dashboard Cite

show abstract

“…In 2009-2010, the heliospheric magnetic field (HMF) intensity reached its lowest value of the space age, which is taken here to be approximately 1965 onwards (Owens et al, 2011;McComas et al, 2012;Lockwood et al, 2012). Simultaneously, near-Earth galactic cosmic ray (GCR) fluxes, inferred from ground-based neutron monitors, peaked at their highest values over the same period (Aslam and Badruddin, 2012;Krymsky et al, 2012), as the HMF modulation effects were weaker (Thomas, Owens, and Lockwood (2013), and references therein). Near-Earth GCR flux can also be inferred from cosmogenic isotopes contained within ice sheets and biomass, allowing the reconstruction of HMF before neutron monitors were in use (e.g.…”

Section: Introductionmentioning

confidence: 95%

Galactic Cosmic Ray Modulation near the Heliospheric Current Sheet

et al. 2014

View full text Add to dashboard Cite

Galactic cosmic rays (GCRs) are modulated by the heliospheric magnetic field (HMF) both over decadal time scales (due to long-term, global HMF variations), and over time scales of a few hours (associated with solar wind structures such as coronal mass ejections or the heliospheric current sheet, HCS). Due to the close association between the HCS, the streamer belt, and the band of slow solar wind, HCS crossings are often associated with corotating interaction regions where fast solar wind catches up and compresses slow solar wind ahead of it. However, not all HCS crossings are associated with strong compressions. In this study we categorise HCS crossings in two ways: Firstly, using the change in magnetic polarity, as either away-to-toward (AT) or toward-to-away (TA) magnetic field directions relative to the Sun and, secondly, using the strength of the associated solar wind compression, determined from the observed plasma density enhancement. For each category, we use superposed epoch analyses to show differences in both solar wind parameters and GCR flux inferred from neutron monitors. For strong-compression HCS crossings, we observe a peak in neutron counts preceding the HCS crossing, followed by a large drop after the crossing, attributable to the so-called 'snow-plough' effect. For weak-compression HCS crossings, where magnetic field polarity effects are more readily observable, we instead observe that the neutron counts have a tendency to peak in the away magnetic field sector. By splitting the data by the dominant polarity at each solar polar region, we find that the increase in GCR flux prior to the HCS crossing is primarily from strong compressions in cycles with negative north polar fields due to GCR drift effects. Finally, we report on unexpected differences in GCR behaviour between TA weak compressions during opposing polarity cycles.

show abstract

“…Krymsky et al [, ] stress that ωτ is a key parameter assumed to be independent of GCR rigidity. Its time variation accounts for the shape and amplitude of 11y modulation.…”

Section: Discussionmentioning

confidence: 99%

“…However, for n2 interval τ is greater near SSN minimum when B drops to the lowest value (see Figure 3a). Krymsky et al [2007Krymsky et al [ , 2012 stress that ωτ is a key parameter assumed to be independent of GCR rigidity. Its time variation accounts for the shape and amplitude of 11y modulation.…”

Section: Mean Time For Diffusive Collisions τmentioning

confidence: 99%

Cosmic ray heliospheric transport study with neutron monitor data

et al. 2015

View full text Add to dashboard Cite

Determining transport coefficients for galactic cosmic ray (GCR) propagation in the turbulent interplanetary magnetic field (IMF) poses a fundamental challenge in modeling cosmic ray modulation processes. GCR scattering in the solar wind involves wave‐particle interaction, the waves being Alfven waves which propagate along the ambient field (B). Empirical values at 1 AU are determined for the components of the diffusion tensor for GCR propagation in the heliosphere using neutron monitor (NM) data. At high rigidities, particle density gradients and mean free paths at 1 AU in B can only be computed from the solar diurnal anisotropy (SDA) represented by a vector A (components Ar, Aϕ, and Aθ) in a heliospherical polar coordinate system. Long‐term changes in SDA components of NMs (with long track record and the median rigidity of response Rm ~ 20 GV) are used to compute yearly values of the transport coefficients for 1963–2013. We confirm the previously reported result that the product of the parallel (to B) mean free path (λ||) and radial density gradient (Gr) computed from NM data exhibits a weak Schwabe cycle (11y) but strong Hale magnetic cycle (22y) dependence. Its value is most depressed in solar activity minima for positive (p) polarity intervals (solar magnetic field in the Northern Hemisphere points outward from the Sun) when GCRs drift from the polar regions toward the helioequatorial plane and out along the heliospheric current sheet (HCS), setting up a symmetric gradient Gθs pointing away from HCS. Gr drives all SDA components and λ|| Gr contributes to the diffusive component (Ad) of the ecliptic plane anisotropy (A). GCR transport is commonly discussed in terms of an isotropic hard sphere scattering (also known as billiard‐ball scattering) in the solar wind plasma. We use it with a flat HCS model and the Ahluwalia‐Dorman master equations to compute the coefficients α (=λ⊥/λ∥) and ωτ (a measure of turbulence in the solar wind) and transport parameters λ||, λ⊥, Gr, Gθs, and an asymmetric gradient Gθa normal to the ecliptic plane. We study their dependence on rigidity (R), p/n intervals, sunspot numbers (SSNs), and solar wind parameters at 1 AU. λ|| exhibits a strong 22y dependence but Gr does not, explaining solar polarity dependence of λ|| Gr. The computed Gr values are an order of magnitude greater than those reported by our colleagues making an ad hoc assumption that α is low (0.01). At high rigidities, the drift contribution at 1 AU is small and unsteady. A new methodology is outlined to compute yearly GCR north‐south anisotropy (Aθ) from the data for a single detector sorted for p/n intervals. We show that Gθa is the main contributor to Aθ in the steady state, and Gθa is shown not correlated with the north‐south excess SSNs.

show abstract

Heliospheric modulation of cosmic rays in solar cycles 19–23

Cited by 8 publications

References 9 publications

Solar Modulation of Cosmic Rays

Solar Modulation of Cosmic Rays

Galactic Cosmic Ray Modulation near the Heliospheric Current Sheet

Cosmic ray heliospheric transport study with neutron monitor data

Contact Info

Product

Resources

About