• U D Desai

Articles written in Proceedings – Section A

• Meteorological and extra-terrestrial causes of the daily variation of cosmic ray intensity

The daily variations of total cosmic ray intensity and the intensities of meson and electron components have been studied at Alimedabad with vertical geiger counter telescopes. The influence of meteorological factors on these variations has been examined, and it has been found that appropriate barometric coefficients for correcting the cosmic ray intensities can be obtained from a consideration of the semidiurnal components of the variations. The barometric coefficients for the three intensities are$$\begin{array}{l} \beta _r = - 4 \cdot 2\% per cm. Hg, \beta _M = - 2 \cdot 4\% per cm. Hg \\ \beta _K = - 14 \cdot 0\% per cm. Hg \\ \end{array}$$ The cosmic ray intensity variations are corrected with the appropriate coefficients for the daily variation of barometric pressure. No significant variation is then left in the electron intensity, implying that variations of this component are mostly caused by the mass absorption effect with a variation of barometric pressure. In total intensity and in meson intensity, on the other hand, there is a significant residual variation of about ·3% in amplitude. This is mainly diurnal in character with a maximum at 0900 hours I.S.T.

Reasons are given for concluding that the meson residual variation is not primarily caused by either the diurnal variation of temperature in the atmosphere or of geomagnetic elements. It is finally concluded that the bulk of the meson residual diurnal variation is extra-terrestrial in origin and is caused by continuous solar emission of cosmic ray particles. This conclusion is discussed in terms of the interpretation of omnidirectional and unidirectional measurements of the diurnal variation by other workers. A connection between changes in the amplitude and the hour of maximum of the diurnal variation has been suggested.