N W Nerurkar
Articles written in Proceedings – Section A
Volume 41 Issue 6 June 1955 pp 245-252
Volume 45 Issue 5 May 1957 pp 341-361
The present status of knowledge concerning the daily variation of meson intensity is reviewed. A solar daily variation of a constant nature arising out of a permanent anisotropy in the cosmic radiation has not so far been established and even if it exists it may not exceed a few tenths of a per cent. However a number of features of a solar daily variation of a highly variable character having on the average a time of maximum on individual days either in the early morning or near noon are known. An attempt is therefore made to interpret the occurrence of a variable anisotropy of cosmic rays to which are attributed the principal experimental observations.
Beams of solar ionized matter with a frozen magnetic field derived from a solar dipole field have been earlier suggested to explain abnormal diurnal variation on magnetically disturbed days through an anisotropy in primary cosmic radiation created by them. The present paper considers that the variable anisotropy is due to such beams but the frozen magnetic field is derived from the magnetic field of the active solar regions and bears no preferential orientation in respect to the solar dipole field. With different orientations of the magnetic field in the beam, the component perpendicular to the solar equatorial plane could be reversed in direction. Depending upon the direction of this component, the anisotropy in the primary radiation gives rise to a daily variation at equatorial stations with maximum either in early morning hours or near noon for a group of days. With the strength of this component of the magnetic field in the range 10−4 to 10−6 gauss and the velocity of the beam between 500 km./sec. and 2,000 km./sec., the daily variation of meson intensity has amplitudes from 0·3 to 1·5%. The simultaneous presence of two such beams gives rise to double the amplitudes or a daily variation with two maxima.