Waves in the cosmic ray north‐south anisotropy with periods of 27 days, 1 year, and 11 years

Swinson, D. B.; Yasue, S.

doi:10.1029/92ja01663

Cited by 12 publications

(6 citation statements)

References 16 publications

(16 reference statements)

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“…Further disagreement on the variance (or invariance) of the ~NS arose from an observation which showed that 27-day waves in the amplitude of the ~NS were modulated with a period of 11 years (Swinson and Yasue, 1991). Baker et al (l 993) attempted a similar analysis to that of Bieber and Pomerantz (1986) but examined the data recorded by many neutron monitors and muon telescopes located throughout the southern hemisphere.…”

Section: Y Symmentioning

confidence: 99%

Analyses of sidereal and solar anisotropies in cosmic rays

1996

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The Sun's interplanetary magnetic field and the solar wind modulate the distrzbution of galactic cosmic-ray particles in the heliosphere. The particles diffuse inward, convect outward and have drifts in the motion of their gyro-centres. Irregularities in the IMF also scatter particles from their gyro-orbits. These processes are the components of solar modulation and produce streaming (and higher-order anisotropies) of particles in the heliosphere. The anisotropies can be investigated at the Earth by examining the count rates of cosmic-ray detectors. The anisotropic streams appear as dmrnal variations m solar and sidereal time in the count rates. Higher-order anisotroples produce generally much smaller semi-diurnal and higher-order variations. Theoretical models of solar modulation predict effects that depend on the polarity of the Sun's magnetic dipole. The solar diurnal and north-south anisotropies can be used to test these predictions. This paper is a short review of analyses of 60 years of cosmic-ray data collected at the Earth for the solar and sMereal diurnal variations present. Past analyses have yielded interesting and controversial results regarding the rigidity spectra and components of these anisotropies. Some of the controversy remains today. Analyses of these anisotropies have also yielded quantitative information about parameters important to solar modulation, such as latitudinal and radial density gradients. The relatively new techniques used for these determinations are explained here. Calculations of these modulation parameters from Earthbased cosmic-ray detectors are reviewed and compared to spaceprobe measurements and theoretical predictions of their values. Recently, investigations of the sidereal and solar diurnal anisotropies have been combined to calculate mean-free-paths of cosmic rays in the heliosphere. The latest conclusions from these analyses are that the parallel mean-free-paths of cosmic rays may depend on the polarity of the Sun's magnetic field. The results of these investigations are included in this paper to indicate the present state of knowledge concerning this facet of cosmic-ray research.

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Section: Y Symmentioning

confidence: 99%

Analyses of sidereal and solar anisotropies in cosmic rays

1996

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“…The lack of agreement on the variance (or invariance) of the 4 NS was increased by an observation which showed that 27-day waves in the amplitude of the 4NS were modulated with a period of 11 years (Swinson and Yasue 1991). Baker et al (1993a) and Baker (1993) used neutron monitor and muon telescope data to examine the North-South asymmetry from 1982 to 1985.…”

Section: Characteristics Of the Sidereal (North-south) Anisotropymentioning

confidence: 99%

Modulation of high‐energy cosmic rays in the heliosphere

Hall¹,

Humble²,

Duldig³

1994

J. Geophys. Res.

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DECLARATIONSI certify that this thesis does not incorporate without acknowledgment any material previously submitted for a degree or diploma in any university; and to the best of my knowledge and belief it does not contain any material previously published or written by another person where due reference is not made in the text. Damian Lindsay Hallll This thesis may be made available for loan and limited copying in accordance with the Copyright Act 1968. Damian Lindsay Hall Ill ABSTRACTThe distribution of galactic cosmic ray particles in the heliosphere is influenced (modulated) by the Sun's interplanetary magnetic field (IMF) and the solar wind. The particles diffuse inward, convect outward and have drifts in the motion of their gyro-centres. They are also scattered from their gyro-orbits by irregularities in the IMF. These processes are the components of solar modulation and produce streaming (anisotropies) of particles in the heliosphere. The anisotropies can be investigated at Earth by examining the count rates of cosmic ray detectors. The anisotropic streams appear as diurnal and semi-diurnal variations in the count rates of cosmic ray recorders in solar and sidereal time. Theoretical models of solar modulation predict effects which are dependent on the polarity of the Sun's magnetic dipole (A >0 or A <0). The solar diurnal and North-South anisotropy can be used to test these predictions.The yearly averaged solar and sidereal diurnal variations in data recorded by seven neutron monitors and ten muon telescopes for the period 1957 to 1990 have been deduced by Fourier analysis methods. The rigidities of the galactic cosmic rays to which these instruments respond encompass the range 10 to 1400 Giga volts (GV). The rigidity spectrum of the solar diurnal anisotropy has been inferred to have a mean spectral index extremely close to zero and an idealised upper limiting rigidity of 100± 25 GV. This is in good agreement with previous determinations. It is shown that this upper limit has a temporal variation between 50 GV and 180 GV and is correlated with the magnitude of the IMF. The rigidity spectrum is likely to be dependent on the polarity of the Sun's magnetic dipole, the spectral index being determined as positive in the A >0 magnetic polarity state and negative in the A <0 polarity state. It is also shown that the amplitude of the anisotropy varies with an 11-year variation and the time of maximum varies with 22-year variation. Both of these variations are shown to be independent of any change in the rigidity spectrum.The solar diurnal anisotropy is also used as a tool to calculate the modulation parameters ?Lip, (the product of the parallel mean-free path and radial density gradient) and Gtzl (an indicator of the symmetric latitudinal density gradient). X G r is found to have a 22-year II variation at all rigidities studied and furthermore to only have rigidity dependence when the heliosphere is in the A >0 magnetic polarity state. It is unlikely that X IIG r has any rigidity dependence in the A <0 polarity s...

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“…However, quasi-periodic changes of the GCR anisotropy connected with the solar rotation, (further in this paper called the 27-day variation) were studied rarely until the work of Alania et al [13][14] for ecliptic plane anisotropy (2D case) and for the north-south component only for polar-located NMs by Owens et al [15]. Swinson and coauthors [16][17][18][19] reported the significant correlation between the 27-day variation of the north-south anisotropy for MTs data and the tilt angle of the heliospheric neutral sheet. Alania et al [13][14] and Gil et al [20] analyzing the periods near the minima epochs of solar activity, demonstrated that the amplitude of the 27-day variation of the 2D anisotropy is less in the negative polarity period than in the positive polarity period of the HMF.…”

Section: Introductionmentioning

confidence: 99%

Quasi-periodic changes of three dimensional solar anisotropy of galactic cosmic rays for 1965-2014

Modzelewska¹,

Alania²

2019

Proceedings of 36th International Cosmic Ray Conference — PoS(ICRC2019)

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We study features of the three dimensional (3D) solar anisotropy of galactic cosmic rays (GCR) for 1965-2014 (almost 5 solar cycles 20-24). We analyze the 27-day variations of the two dimensional (2D) GCR anisotropy in the ecliptic plane, and the north-south anisotropy normal to the ecliptic plane. We study the dependence of the 27-day variation of the 3D GCR anisotropy on the solar cycle and solar magnetic cycle. We demonstrate that the 27-day variations of the GCR intensity and anisotropy can be used as an important tool to study solar wind, solar activity and heliosphere. We show that behavior of the 27-variation of the 3D anisotropy verifies an existence of a stable longlived active heliolongitudes on the sun. This finding illustrates usefulness of the 27-day variation of the GCR anisotropy as a unique proxy to study solar wind, solar activity and heliosphere. We distinguish a tendency of the 22-year changes of the amplitudes of the 27-day variation of the 2D anisotropy connected with the solar magnetic cycle. We demonstrate that the amplitudes of the 27-day variation of the north-south component of the anisotropy vary upon the 11 year solar cycle, however, a dependence of the solar magnetic polarity hardly can be recognized. We show that the 27-day recurrences of the GG index and At component are in a high positive correlation, and both are highly correlated with By component of the heliospheric magnetic field.

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Waves in the cosmic ray north‐south anisotropy with periods of 27 days, 1 year, and 11 years

Cited by 12 publications

References 16 publications

Analyses of sidereal and solar anisotropies in cosmic rays

Analyses of sidereal and solar anisotropies in cosmic rays

Modulation of high‐energy cosmic rays in the heliosphere

Quasi-periodic changes of three dimensional solar anisotropy of galactic cosmic rays for 1965-2014

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