Galactic cosmic ray diurnal modulation, interplanetary magnetic field intensity and the planetary index Ap

Ahluwalia, H. S.

doi:10.1029/1999gl003716

Cited by 8 publications

(5 citation statements)

References 20 publications

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“…They found that the amplitudes of FDs are linearly correlated with the parameter 'BmaxVmax,' as mentioned earlier. They obtained cc = 0.70; cc = 0.66 if only Bmax is considered and cc = 0.37 if only Vmax is considered; their experience is similar to our own with Rc variations [Ahluwalia, 2000c]. One should verify if BV data also reproduce GCR variations during each FD studied by Cane et al [1996].…”

Section: Discussionsupporting

confidence: 72%

“…However, the physical process involved in GCR modulation is not new; it is still defined by the parameter BV. Our empirical approach suggests that individually V may not be important in explaining the subtle features of modulation as compared to B [ Ahluwalia , 2000c], but the product BV is an important modulation parameter.…”

Section: Cosmic Ray Minicyclementioning

confidence: 99%

“… Ahluwalia [1992b] discovered that an important modulation parameter is linearly correlated with the intensity (B) of IMF measured in situ at Earth's orbit; he showed that the limiting GCR rigidity (Rc) applicable to the steady state diurnal anisotropy (during 1964 to 1987) is linearly correlated with the annual mean value of B (the value of Rc determines the amplitude of the diurnal anisotropy so that modulation extends to higher rigidities at large B). A recent update to the analysis [ Ahluwalia , 2000c] confirmed that the correlation between Rc and B continued to be high until 1998 (cc = 0.71) and that between Rc and V very low (cc = 0.37). Also, Rc was shown to be poorly correlated (cc = 0.56) to IMF turbulence range considered by Bieber et al [1993], supporting their inference that scattering processes described by the resonant magnetostatic theory may have little role in causing the observed GCR modulation.…”

Section: Introductionmentioning

confidence: 99%

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Solar wind modulation of galactic cosmic rays

Ahluwalia

2003

Geophysical Research Letters

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[1] We have analyzed the annual mean hourly data for the solar wind speed (V), the interplanetary magnetic field (IMF) intensity (B), and the neutron monitor (NM) rates for 1964 -1998, covering three sunspot number (SSN) cycles (20, 21, 22). The analysis brings out some of the steady state characteristics of the long-term changes in the observed galactic cosmic ray (GCR) modulation and the 'mini' cycle. We find that BV time series reproduces the observed variations of a variety of phenomena, including the 11-yr and the 27-day GCR modulations. We reaffirm that convective removal of GCR by the solar wind accounts for a major part of the observed modulations in the inner heliosphere.

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Section: Discussionsupporting

confidence: 72%

Section: Cosmic Ray Minicyclementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Solar wind modulation of galactic cosmic rays

Ahluwalia

2003

Geophysical Research Letters

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“…We then rewrite as This is a very interesting result. It suggests three possibilities for the solar cycle variation of modulation; namely, rb can slowly vary with time, V can vary with time, and so can B ; empirical evidence suggests that modulation depends more strongly on B than on V [ Ahluwalia , 1992, 2000c; Belov , 2000]. Measurements made in space indicate that values of B and V vary by a factor of 2 at Earth's orbit during a solar cycle and so does the observed modulation at >1 GV.…”

Section: Force Field Approachmentioning

confidence: 99%

Cycle 20 solar wind modulation of galactic cosmic rays: Understanding the challenge

Ahluwalia

2005

J. Geophys. Res.

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[1] It is well known that time variations of galactic cosmic rays for cycle 20 (1964-1976) challenge our understanding of the heliospheric dynamics and the physical processes involved in causing observed modulations. Several interesting questions have been raised over the years. We attempt to provide some plausible answers based on analyses of cosmic ray data obtained with detectors on the ground, on balloons, and on satellites; median rigidity of response of these detectors to the cosmic ray spectrum covers a range of rigidities (R) from 1 to 70 GV. In particular, we explore the observed correlation between hourly rates of neutron monitors and the time series of the product of solar wind velocity (V) and interplanetary magnetic field intensity (B) at Earth's orbit. Local convection is identified as a contributor to ''steps'' in cosmic ray time variations near Earth and in the outer heliosphere. The amplitude of 11-year modulation varies as 1/R; data do not support the concept of ''transition'' rigidity for modulation. We argue that heliosheathrelated modulation effects are minimal at Earth's orbit at R > 3 GV. Heuristic considerations suggest that the space-dependent part of the diffusion coefficient should vary as 1/B (not 1/B 2 ). We relate modulation function to the product BV, suggesting it plays a significant role in the solar modulation of cosmic rays.

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“…Munakata et al [6] use Rc = 100 GV for NagV-MT data (35N 137E). We use Rc value computed from the regression relation between Rc, B [24] for the entire period (1971-2017) for NagV-MT (Ro = 10 GV) to compare our results with theirs; the coupling function (W) derived by Murakami et al [25][26] for NagV-MT are used to compute A and resolved into the east-west (Af) and radial (Ar) components [3]; data are corrected for negative temperature effect using empirical vector in 6h LT direction with an amplitude of 0.11% [9].…”

Section: Analysis Proceduresmentioning

confidence: 99%

Study of cosmic ray ratio of free paths normal and parallel to IMF with muon data

Ahluwalia¹,

Modzelewska²

2019

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

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The galactic cosmic ray (GCR) solar diurnal anisotropy (SDA) data of Nagoya vertical muon telescope (NagV-MT) are used to compute the ratio (a) of GCR free paths normal and parallel to the mean interplanetary magnetic field (IMF) B. They are compared to the corresponding values for the neutron monitors (NMs) of the global network, computed earlier, for three sunspot cycles (21-23) and parts of the other two (19, 24). Current modulation theories do not provide any guidance for the value and rigidity dependence of α. We use a flat heliospheric current sheet and master equations derived by Ahluwalia and Dorman [1997] for computing a using SDA data for NagV-MT. Preliminary results for its rigidity dependence and correlation with solar activity for positive (p) and negative (n) polarity intervals of B at 1 AU are noted. Results challenge the validity of old results and conceptual understanding of GCR modulation processes in the heliosphere.

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Galactic cosmic ray diurnal modulation, interplanetary magnetic field intensity and the planetary index Ap

Cited by 8 publications

References 20 publications

Solar wind modulation of galactic cosmic rays

Solar wind modulation of galactic cosmic rays

Cycle 20 solar wind modulation of galactic cosmic rays: Understanding the challenge

Study of cosmic ray ratio of free paths normal and parallel to IMF with muon data

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