‘sidereal’ cosmic-ray diurnal variations

Swinson, D. B.

doi:10.1029/ja074i024p05591

Cited by 65 publications

(42 citation statements)

References 11 publications

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“…The NS anisotropy derived in this way is very sensitive to the stability of operations of two independent detectors and can be easily affected by unexpected changes of instrumental and/or environmental origins. Due to the 23.4°inclina-tion of Earth's rotation axis from the ecliptic normal, the NS anisotropy normal to the ecliptic plane can be also observed as a diurnal variation of count rate in sidereal time with the maximum phase at approximately 06:00 or approximately 18:00 local sidereal time (Swinson 1969). A possible drawback of deriving the NS anisotropy from the sidereal diurnal variation is that the expected amplitude of the sidereal diurnal variation is roughly ten times smaller than that of the solar diurnal variation.…”

Section: Introductionmentioning

confidence: 99%

The spatial density gradient of galactic cosmic rays and its solar cycle variation observed with the Global Muon Detector Network

et al. 2014

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We derive the long-term variation of the three-dimensional (3D) anisotropy of approximately 60 GV galactic cosmic rays (GCRs) from the data observed with the Global Muon Detector Network (GMDN) on an hourly basis and compare it with the variation deduced from a conventional analysis of the data recorded by a single muon detector at Nagoya in Japan. The conventional analysis uses a north-south (NS) component responsive to slightly higher rigidity (approximately 80 GV) GCRs and an ecliptic component responsive to the same rigidity as the GMDN. In contrast, the GMDN provides all components at the same rigidity simultaneously. It is confirmed that the temporal variations of the 3D anisotropy vectors including the NS component derived from two analyses are fairly consistent with each other as far as the yearly mean value is concerned. We particularly compare the NS anisotropies deduced from two analyses statistically by analyzing the distributions of the NS anisotropy on hourly and daily bases. It is found that the hourly mean NS anisotropy observed by Nagoya shows a larger spread than the daily mean due to the local time-dependent contribution from the ecliptic anisotropy. The NS anisotropy derived from the GMDN, on the other hand, shows similar distribution on both the daily and hourly bases, indicating that the NS anisotropy is successfully observed by the GMDN, free from the contribution of the ecliptic anisotropy. By analyzing the NS anisotropy deduced from neutron monitor (NM) data responding to lower rigidity (approximately 17 GV) GCRs, we qualitatively confirm the rigidity dependence of the NS anisotropy in which the GMDN has an intermediate rigidity response between NMs and Nagoya. From the 3D anisotropy vector (corrected for the solar wind convection and the Compton-Getting effect arising from the Earth's orbital motion around the Sun), we deduce the variation of each modulation parameter, i.e., the radial and latitudinal density gradients and the parallel mean free path for the pitch angle scattering of GCRs in the turbulent interplanetary magnetic field. We show the derived density gradient and mean free path varying with the solar activity and magnetic cycles.

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Section: Introductionmentioning

confidence: 99%

The spatial density gradient of galactic cosmic rays and its solar cycle variation observed with the Global Muon Detector Network

et al. 2014

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“…Further discussion of any true galactic anisotropies appearing at these rigidities will be deferred until Chapter 4. Swinson (1969) proposed a different explanation for the phase differences in the sidereal diurnal variation observed from opposite hemispheres. He proposed that the anisotropy responsible for the sidereal diurnal variation was IMF sector polarity dependent and was directed perpendicular to the ecliptic plane.…”

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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“…Jacklyn (1966) attributed this to a bi-directional streaming (or pitch-angle anisotropy) along the local galactic magnetic field. Swinson (1969) disagreed, proposing instead that the anisotropy responsible for the sidereal diurnal variation was IMF sector polarity-dependent and directed perpendicular to the ecliptic plane. The streaming of particles perpendicular to the ecliptic had been described by Berkovitch (1970), and Swinson realised that the anisotropy would have a component in the equatorial plane.…”

Section: North-south Anisotropymentioning

confidence: 99%

“…It turned out that both Jacklyn (1966) and Swinson (1969) were correct and that a bi-directional sidereal anisotropy and a sidereal anisotropy resulting from the north-south anisotropy coexisted in the 1950s and 1960s. It would appear that the amplitude of the bidirectional anisotropy diminished greatly in the early 1970s (Jacklyn & Duldig 1985;Jacklyn 1986) and has not recovered, a result that remains unexplained.…”

Section: North-south Anisotropymentioning

confidence: 99%

Australian Cosmic Ray Modulation Research

Duldig

2001

Publ. – Astron. Soc. Aust

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Australian research into variations of the cosmic ray flux arriving at the Earth has played a pivotal role for more than 50 years. The work has been largely led by the groups from the University of Tasmania and the Australian Antarctic Division and has involved the operation of neutron monitors and muon telescopes from many sites. In this paper the achievements of the Australian researchers are reviewed and future experiments are described. Particular highlights include: the determination of cosmic ray modulation parameters; the development of modelling techniques of Ground Level Enhancements; the confirmation of the Tail-In and Loss-Cone Sidereal anisotropies; the Space Ship Earth collaboration; and the Solar Cycle latitude survey.Comment: 47 pages, 37 figures, LaTeX, invited review, in press PASA 18(1). HTML version available at http://www.atnf.csiro.au/pasa/18_1/duldig/paper

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‘sidereal’ cosmic-ray diurnal variations

Cited by 65 publications

References 11 publications

The spatial density gradient of galactic cosmic rays and its solar cycle variation observed with the Global Muon Detector Network

The spatial density gradient of galactic cosmic rays and its solar cycle variation observed with the Global Muon Detector Network

Modulation of high‐energy cosmic rays in the heliosphere

Australian Cosmic Ray Modulation Research

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