Cosmic ray transverse gradient for a Hale Cycle

Ahluwalia, H. S.

doi:10.1029/94ja02358

Cited by 24 publications

(30 citation statements)

References 24 publications

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“…Recently, a spate of studies have quantitatively derived the symmetric latitudinal gradient from the solar diurnal anisotropy of cosmic rays with rigidities from 17 to 300 GV (Bieber and Chert, 1991a, b;Chen and Bieber, 1993;Hall etal., 1993bHall etal., , 1994aAhluwalia and Sabbah, 1993;Ahluwalia, 1994). The results of these studies are of paramount importance to our understanding of modulation and can be directly compared to the predictions of drift theories.…”

Section: The Modulation Parameter G /Z/ In Section 2 It Was Noted Thamentioning

confidence: 90%

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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: The Modulation Parameter G /Z/ In Section 2 It Was Noted Thamentioning

confidence: 90%

“…The median rigidities of these instruments were between 17 and 300 GV. Ahluwalia (1993Ahluwalia ( , 1994 included temperature corrections of the same ion chamber data analysed originally by Bieber and Chen (1991 a) and still concluded that All G r does not depend on rigidity in any way.…”

Section: Parametersmentioning

confidence: 99%

Analyses of sidereal and solar anisotropies in cosmic rays

1996

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“…For example, 11 year and 22 year variations of the annual mean counting rate of diverse detectors [Ahluwalia, 1992, 1994a, Ahluwalia and Wilson, 1996, and references therein], secular variation in the limiting rigidity of galactic cosmic rays [Ahluwalia and Riker, 1987; Ahluwalia and Sabbah, 1993a, and references therein], long-term changes in the parameters applicable to the diurnal anisotropy [Ahluwalia, 1988;Ahluwalia and Sabbah, 1993b] and its bigher harmonics [Ahluwalia and Fikani, 1996a, b], as well as the observed changes in the tranSVerse gradients [Ahluwalia and Sabbah, 1993c;Ahluwalia, 1994bAhluwalia, , 1996; Ahluwalia and Dotman, 1997]. Several creative ideas have been suggested to understand these observations.…”

Section: Cosmic Ray Sol• Modulation I S W•fno•sed In a Variety Ofmentioning

confidence: 99%

Galactic cosmic ray intensity variations at a high latitude sea level site 1937–1994

Ahluwalia¹

1997

J. Geophys. Res.

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Abstract. We have created an extended cosmic ray data string (1937 -1994) by combining data obtained with ion chambers at Cheltenham/Fredericksburg (1937 -1972) and Yakutsk (1953Yakutsk ( -1994. Both represent high-latitude, sea level sites, with an atmospheric cutoff of about 4 GV. Their common median rigidity of response to galactic cosmic ray spectrum is 67 GV. This data string represents the longest continuous cosmic ray intensity variations record yet. Therefore it is useful for the cosmic ray modulation studies over a longer time period. We show that there is no striking quantitative correspondence between the amplitudes of solar activity cycles and cosmic ray modulation over six cycles. However, an inverse correlation is apparent between the two. Moreover, the results on the durations of the two are ambiguous. Flat-topped recovery pattern predicted for even cycles (A > 0), at lower rigidities, is not observed in the ion chamber data. We speculate that three solar activity cycle quasi-periodicity may be present in the extended data string. Its origin is not identified yet. The quasiperiodicity is shown to exist also in the planetary index Ap data. As such, it may represent a characteristic feature of the solar wind source region on the Sun as yet unexplored. The odd cycles, with a negative polarity in the solar northern hemisphere, yield a better linear correlation between galactic cosmic ray intensity decrease and Ap than even cycles and A > 0 epochs.

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“…The Sun's polarity is classified by the dominant solar polar polarity, A, being outwards in the northern pole (denoted A > 0) or inwards (denoted A < 0) for this purpose (e.g. Ahluwalia, 1994;Potgieter, 2013). Due to the differences in drift patterns and the HMF field on these long timescales, it is reasonable to expect that a change in the preferred direction of anisotropy on shorter timescales between the two polarities is possible.…”

Section: Introductionmentioning

confidence: 99%

Decadal trends in the diurnal variation of galactic cosmic rays observed using neutron monitor data

et al. 2017

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Abstract. The diurnal variation (DV) in galactic cosmic ray (GCR) flux is a widely observed phenomenon in neutron monitor data. The background variation considered primarily in this study is due to the balance between the convection of energetic particles away from the Sun and the inward diffusion of energetic particles along magnetic field lines. However, there are also times of enhanced DV following geomagnetic disturbances caused by coronal mass ejections or corotating interaction regions. In this study we investigate changes in the DV over four solar cycles using ground-based neutron monitors at different magnetic latitudes and longitudes at Earth. We divide all of the hourly neutron monitor data into magnetic polarity cycles to investigate cycleto-cycle variations in the phase and amplitude of the DV. The results show, in general, a similarity between each of the A < 0 cycles and A > 0 cycles, but with a phase change between the two. To investigate this further, we split the neutron monitor data by solar magnetic polarity between times when the dominant polarity was either directed outward (positive) or inward (negative) at the northern solar pole. We find that the maxima and minima of the DV changes by, typically, 1-2 h between the two polarity states for all non-polar neutron monitors. This difference between cycles becomes even larger in amplitude and phase with the removal of periods with enhanced DV caused by solar wind transients. The time difference between polarity cycles is found to vary in a 22-year cycle for both the maximum and minimum times of the DV. The times of the maximum and minimum in the DV do not always vary in the same manner between A > 0 and A < 0 polarity cycles, suggesting a slight change in the anisotropy vector of GCRs arriving at Earth between polarity cycles. Polar neutron monitors show differences in phase between polarity cycles which have asymptotic directions at mid-to-high latitudes. All neutron monitors show changes in the amplitude of the DV with solar polarity, with the amplitude of the DV being a factor of 2 greater in A < 0 cycles than A > 0 cycles. In most cases the change in timing of the maximum /minimum is greatest with the stations' geomagnetic cut-off rigidity shows little variation in the DV phase with latitude. We conclude that the change in the DV with the dominant solar polar polarity is not as simple as a phase change, but rather an asymmetric variation which is sensitive to the neutron monitor's asymptotic viewing direction.

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Cosmic ray transverse gradient for a Hale Cycle

Cited by 24 publications

References 24 publications

Analyses of sidereal and solar anisotropies in cosmic rays

Analyses of sidereal and solar anisotropies in cosmic rays

Galactic cosmic ray intensity variations at a high latitude sea level site 1937–1994

Decadal trends in the diurnal variation of galactic cosmic rays observed using neutron monitor data

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