Abstract
THE solar diurnal anisotropy of cosmic rays is attributed to the bulk streaming of the cosmic ray gas caused by the corotating interplanetary magnetic field that is “rigidly attached to the Sun”1,2. By analogy with the classical Compton–Getting effect3, a(R), the amplitude of the daily variation at magnetic rigidity R is related to the ratio of particle speed v and the bulk streaming velocity u 
where γ is the exponent of the differential spectrum. Because, at the orbit of the Earth, u≈450 km s−1 a neutron monitor with mean rigidity of response about 10 GeV and atmospheric threshold 1 GeV should observe an amplitude extrapolated through the atmosphere to free space of about 0.7 per cent.
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JACKLYN, R., DUGGAL, S. & POMERANTZ, M. Solar Diurnal Anisotropy of Cosmic Rays. Nature 223, 601–602 (1969). https://doi.org/10.1038/223601a0
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DOI: https://doi.org/10.1038/223601a0
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