The Upper Limiting Primary Rigidity of the Cosmic Ray Solar Anisotropy

Abstract

SummaryA method of determining the upper limiting rigidity of the solar diurnal variation of the cosmic ray primaries in free space is described. It involves a comparision of the response to the anisotropy of neutron monitors at sea level and of meson telescopes underground. Making use of the model for the free-space first harmonic proposed by Rao, McCracken, and Venkatesan, the annual average value for the upper limiting rigidity (Ru) in 1958 is estimated to have been 95 GV with an error of estimate of about 10-20 GV. Changes in the observed annual mean daily variation between 1958 and 1962 indicate that Ru may have decreased by about 20-40 GV over this period, but a more refined analysis is needed to confirm this.Changes in Ru could also influence a sidereal daily variation as observed at the Earth. Evidence is presented for such an effect, from the observations underground at Hobart.It is shown that the annual average pressure-corrected solar diurnal variation observed at a depth of 40 m.w.e. must be largely under the control of the solar anisotropy. The most significant evidence presented comes from observations in three different directions underground at Hobart during 1961 and 1962. The first harmonics of the solar daily variations observed in these directions have been found to be broadly compatible with the model for the anisotropy proposed by Rao, McCracken, and Venkatesan.We also present the results of an investigation of the response of an underground telescope to generalized free-space first and second harmonics, for different approximations to the geomagnetic field and for small and large sets of arrival directions.

The cosmic ray solar diurnal anisotropy

“…The responses of other detectors (e.g. various meson telescopes and underground detectors) to the diurnal modulation have also been calculated (Jacklyn and Humble, 1965;Sarabhai and Subramanian, 1965;Peacock et al, 1968;Mori, 1968;Jacklyn et al, , 1970Ahluwalia and Ericksen, 1970;Fujii et al, 1970;Kuzmin et al, 1970;Peacock, 1970).…”

“…Many investigators have determined one or more of the spectral parameters (Dor- , 1958Kuzmin, 1960;Duggal et al, 1961;Pomerantz et al, 1962;Sandstr6m et al, 1962;Kuzmin et aI., 1963Kuzmin et aI., , 1965Bercovitch, 1963 ;Rao et al, 1963 ;Kane, 1964;Jacklyn and Humble, 1965;Kolomeets et al, 1965;Faller and Marsden, 1965;Mori et al, 1965;Kawasaki, 1968;Peacock et al, 1968;Hashim et al, 1968;Jacklyn et al, , 1970Peacock, 1970;Ahluwalia and Ericksen, 1970;Willets et al, 1970). A critical appraisal of the most recent results indicates that over the range from a few GV to about 100 GV the solar diurnal anisotropy is essentially independent of rigidity (m--0).…”

Modulation of high‐energy cosmic rays in the heliosphere

“…Jacklyn and Humble (1965) found that P u was not constant and that this may have caused the amplitude to have an apparent variation. Duggal et al (1967) presented results indicating that the amplitude of the solar diurnal variation was not invariant.…”

“…The region of equality should indicate the most reasonable and accurate value of P u to use in a determination of the free-space parameters describing the anisotropy. This is the basis of all previous analyses of the rigidity spectrum of 4sco (Jacklyn and Humble 1965, Jacklyn et al 1969, Ahluwalia and Erickson 1969, Humble 1971, Alania et al 1983, Ahluwalia and Riker 1987 and also the basis of the following methods of determining the spectrum of the solar diurnal anisotropy.…”

Australian Cosmic Ray Modulation Research

“…Rao et al (1963) found that the anisotropy was independent of rigidity (γ = 0) and P u was 200 GV. Further analysis by Jacklyn & Humble (1965) found that P u was not constant. This was confirmed by Peacock & Thambyahpillai (1967) and Peacock, Dutt & Thambyahpillai (1968), who showed P u varying from 130 GV during the period 1960-1964to 70 GV in 1965.…”