Anisotropies of galactic cosmic rays in the solar system

Patel, D.; Sarabhai, V.; Subramanian, Ganesh

doi:10.1016/0032-0633(68)90125-6

Cited by 17 publications

(2 citation statements)

References 7 publications

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“…The average value is 0.7 + 0.3. This value is consistent with previous findings [Patel et al, 1968;Rao and Agrawal, 1970;Subramanian, 1971] which used a single power law for this rigidity range, for the neutron monitor data. Second, aside from even solar cycle maxima, the high-rigidity exponent ¾2 is also essentially constant, with an average value of-0.4 + 0.2.…”

Section: The Value Of R• For the Period 1978 To 1985 Is Somewhat High Insupporting

confidence: 93%

“…From previous studies of the semidiurnal variation [Quenby and Lietti, 1968;Patel et al, 1968;Rao and Agrawal, 1970;Fujii, 1971;Pathak, 1972], it is known that the distribution of amplitudes is rigidity d•dent, unlike the case for the diurnal variation [Rao et al, 1963;Ahluwalia andRiker, 1987]. In addition, it has been found that a break or peak occurs in the semidiurnal spectrum [Fujii, 1971;Zusmanovich and Mirkin, 1983].…”

Section: Variational Spectrummentioning

confidence: 99%

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Cosmic ray solar semidiurnal anisotropy: 1. Treatment of experimental data

Ahluwalia¹,

Fikani²

1996

J. Geophys. Res.

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We have analyzed data obtained with 39 globally distributed detectors, with median primary rigidity of response (Rm) in the range: 10 GV ≤ Rm ≤ 330 GV, for the period 1953 to 1992. The time interval covers several epochs of solar activity maxima, minima, and polar field reversals. Data are sparse for earlier period but adequate after 1970. We have investigated long‐term changes in the parameters applicable to the annual mean solar semidiurnal variation. We show that its dependence on the median asymptotic latitude of viewing (λm) is given by cos2 λm. The data are consistent with a double power law fit in rigidity for the entire period of our study. The power law exponents are given by γ1, = 0.7 ± 0.3 (if R ≤ Rp,) and γ2 = − 0.4 ± 0.2 (if R > Rp), where Rp is the peak primary rigidity. The values of Rp near maximum for even solar activity cycles (20, 22) are quite large (∼125 GV) compared to other periods. These large values lie close to the epochs of magnetic polarity reversals from negative (q A < 0) to positive (q A > 0) in the northern hemisphere of Sun. During these times, the exponent γ2 acquires large negative values. Near solar activity minima, the values of Rp, are among the lowest at about 40 GV. We have also computed the mean limiting primary rigidity (Rc) for each year. The values of Rc lie close to 50 GV for solar activity minima and near 100 G V for maxima. In other words, the values of Rc are very close to those of Rp. Moreover, the correspondence between them is good. Both exhibit solar as well as Hale cycle variations.

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Section: The Value Of R• For the Period 1978 To 1985 Is Somewhat High Insupporting

confidence: 93%

Section: Variational Spectrummentioning

confidence: 99%

Cosmic ray solar semidiurnal anisotropy: 1. Treatment of experimental data

Ahluwalia¹,

Fikani²

1996

J. Geophys. Res.

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The cosmic ray solar diurnal anisotropy

Pomerantz

Duggal

1971

Space Sci Rev

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This paper reviews the present state of knowledge concerning the diurnal and semidiurnal variations in the galactic cosmic ray intensity. The analytical procedures that are required for extracting from the original data the desired information concerning the characteristics of the anisotropies outside the magnetosphere are described. These include corrections for atmospheric fluctuations, the determination of the amplitudes and phases of the daily variations, and their interpretation in terms of the free space anisotropies that give rise to them. The experimental results concerning the 24-h wave, including its long-term variations with periods of one and two solar cycles, and the characteristics of the total dmrnal anisotropy are then discussed. The semidmrnal amsotropy is considered next. Transient anisotropies which manifest themselves as day-to-day variations, recurrence tendencies, cosmic ray storms, and diurnal variation trains, and which can introduce appreciable changes in the spectral parameters, are also of interest. The evolution of theoretical models developed to account for the diurnal and semidiurnal anisotropies, and fluctuations thereof, are then discussed in the light of the experimental results. Finally, the general features that are now well established, and the nature of the remaining problems, are summarized.

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Solar modulation of galactic cosmic radiation

Rao

1972

Space Sci Rev

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In this review an attempt is made to present an integrated view of the solar modulation process that cause time variation of cosmic ray particles. After briefly surveying the relevant large and small scale properties of the interplanetary magnetic fields and plasma, the motion of cosmic ray particles in the disordered interplanetary magnetic fields is discussed. The experimentally observed long term variations of different species of cosmic ray particles are summarised and compared with the theoretical predictions from the diffusion-convection model. The effect of the energy losses due to decelaration in the expanding solar wind are clearly brought out. The radial density gradient, the modulation parameter and their long term variation are discussed to understand the dynamics of the modulating region. The cosmic ray anisotropy measurements at different energies are summarised. At high energies (E> 1 GeV), the average diurnal anisotropy is shown to be energy independent and along the 18.00 h direction consistent with their undergoing partial corotation with the sun. The average semi-diurnal anisotropy seems to vary with energy as E +1 and incident from a direction perpendicular to the interplanetary field line, consistent with the semi-diurnal component being produced by latitudinal gradients. Both the diurnal and semi-diurnal components are shown to be practically time invariant. On a day to day basis, however, the anisotropy characteristics such as the exponent of variation, the amplitude and the phase show very high variability which are interpreted in terms of convection and variable field aligned diffusion due to the redistribution of the galactic cosmic ray density following transient changes in the interplanetary medium. The anisotropy observation at low energies (E< 100 MeV) are, however, not explained by the theory.The rigidity dependence and the anisotropies during short term variations such as Forbush decreases are discussed in terms of the proposed field models for the interplanetary field structure and are compared with the observed rigidity dependence of long term variations. The data pertaining to the 27 day corotating Forbush decreases and their association with enhanced diurnal variation are also presented. The relationship between the energetic storm particle events which are caused by the acceleration of particles in the shock fronts and the Forbush decreases which are caused by the exclusion of galactic particles by the enhanced field structure in the same fronts are clearly brought out. Thus the recurrent increases at low energies and recurrent decreases at high energies may both be caused by the field structure in the shock front. In conclusion, the properties of the very short period fluctuations (18-25 cph) are summarised.

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Anisotropies of galactic cosmic rays in the solar system

Cited by 17 publications

References 7 publications

Cosmic ray solar semidiurnal anisotropy: 1. Treatment of experimental data

Cosmic ray solar semidiurnal anisotropy: 1. Treatment of experimental data

The cosmic ray solar diurnal anisotropy

Solar modulation of galactic cosmic radiation

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