Solar modulation origin of ‘sidereal’ cosmic ray anisotropies

Swinson, D. B.

doi:10.1029/ja076i019p04217

Cited by 38 publications

(25 citation statements)

References 12 publications

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“…This is called the North-South Anisotropy (Ns). The effect was conclusively demonstrated by analysing underground muon data (Swinson 1971). In reality the streaming of particles perpendicular to the ecliptic plane is a net anisotropic flow caused mainly by curvature and gradient drifts in the IMF.…”

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

confidence: 75%

“…(See equation 1.6 and also Chapter 4 for the relation between the North-South Anisotropy and Gr). Swinson (1969Swinson ( , 1971 inferred that Gr of particles with rigidities greater than 100 GV was positive from 1965 to 1970. This is consistent with spacecraft observations of Gr.…”

Section: Radial Density Gradientmentioning

confidence: 99%

“…No other studies of the spectrum have been done except by Swinson (1971) Table 1.1) but recent studies conclude that these mean-free paths may be magnetic polarity dependent Chen 1991b, Chen andBieber 1993). In Chapter 5 this dependence of Adi (or lack of it) on the IMF polarity is investigated by using the anisotropies (solar diurnal and North-South) obtained from neutron monitor data.…”

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confidence: 99%

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

confidence: 75%

Section: Radial Density Gradientmentioning

confidence: 99%

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confidence: 99%

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Modulation of high‐energy cosmic rays in the heliosphere

Hall¹,

Humble²,

Duldig³

1994

J. Geophys. Res.

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“…There should therefore be an additional component to the sidereal anisotropy at 1800 hours ST when the field points W-and a component at 0600 hours ST when the field points E+, after correction for deflection in the geomagnetic field. An example of these field dependent components to the sidereal anisotropy can be seen in Figure 1; this effect has been attributed [Swinson, 1969[Swinson, , 1971] to the oppositely directed density gradient streaming for the two opposite field senses as noted earlier. A measure of the magnitude and direction of the field dependent streaming can be obtained by taking the vector difference between the solar diurnal variation for the field pointing E+ and that for the field pointing W-.…”

Section: Introductionmentioning

confidence: 58%

Field dependent cosmic ray streaming at high rigidities

Swinson¹

1976

J. Geophys. Res.

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Data from underground µ meson telescopes at depths of 25, 40, and 80 mwe covering the period 1965–1973 have been analyzed as a function of interplanetary magnetic field direction. Cosmic ray streaming both in and perpendicular to the ecliptic plane, with directions dependent on the sense of the interplanetary magnetic field, is observed throughout the period at all depths. The field dependent streaming in the ecliptic plane exhibits some variability in amplitude and phase but contains a component in the direction perpendicular to the interplanetary magnetic field direction which is consistent with B × ▽N streaming due to a perpendicular cosmic ray density gradient pointing southward (higher density below the ecliptic plane than above it). In the case of the field dependent streaming perpendicular to the ecliptic plane the direction of the streaming has remained remarkably consistent over the 9‐year period. One possible source of this streaming is B × ▽N streaming due to a radial heliocentric cosmic ray density gradient; this possibility is discussed along with other possible sources. There does not appear to be an obvious variation in the amplitude of the field dependent streaming either in or perpendicular to the ecliptic plane with increasing rigidity; both effects are still apparent at rigidities well above the 52‐GV threshold rigidity of the Socorro 80‐mwe telescope. The amplitudes of both anisotropies appear larger at solar maximum than at solar minimum.

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“…One of the characters particularly important is the fact that in spite of its finite daily amplitude, yearly average of the P2-type component becomes very small or vanishes, as a result of its annual modulation due to the earth's annual motion around the sun. Connecting with above fact, Paper I mentioned a suggestive model that the anisotropy in sidereal time can be attributed to solar modulation of cosmic rays in the inner part of the solar system, which yields a net anisotropic flow perpendicular to the plane of ecliptic over a year; this flow is observed as a sidereal anisotropy with maxima at eigen phases of 6 hr or 18 hr (SWINSON, 1969(SWINSON, , 1971KRIVOSHAPKIN, 1970). Paper I has also demonstrated the facts that definite sidereal anisotropies were observed in the differences between the diurnal vectors of the ion chamber at Cheltenham and Christchurch for 22 years (Part 3), and significant and systematic annual changes of solar diurnal variations of the directional intensity at Hilt.…”

Section: Introductionmentioning

confidence: 99%

Annual modulation of solar diurnal variation of the cosmic ray nucleonic component in three-dimensional space.

Mori

1975

J. geomagn. geoelec

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A study was made of the annual modulation of the cosmic ray solar diurnal variation to search one of the characteristics of the three-dimensional cosmic ray anisotropy in space. The present analysis, using the neutron monitor data from the worldwide network for the period of [1964][1965][1966][1967][1968], is the extension work to confirm the results already derived from the meson data by Nagashima et al. In order to show the annual change of solar diurnal variations clearly, differences between the diurnal vectors at conjugate pairs of the observational stations in northern and southern hemispheres were exclusively utilized. A significant and systematic annual variation is found in the harmonic dial of monthly difference vectors moving in an ellipse having its major axis with the range of about 0.05% and the direction in 9 hr of FebruaryAugust in a year. This annual movement of solar diurnal variations can be interpreted in the framework of Nagashima's theory, due to the P2-type diurnal term arising from the second harmonic component of the cosmic ray solar anisotropy in space. The space distribution responsible for the annual variation of the nucleonic component is re-examined in terms of both solar and sidereal time variations.

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Solar modulation origin of ‘sidereal’ cosmic ray anisotropies

Cited by 38 publications

References 12 publications

Modulation of high‐energy cosmic rays in the heliosphere

Modulation of high‐energy cosmic rays in the heliosphere

Field dependent cosmic ray streaming at high rigidities

Annual modulation of solar diurnal variation of the cosmic ray nucleonic component in three-dimensional space.

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