F-scatter and cosmic radio noise on 25 Mc./s. at Ahmedabad

In the cosmic noise records on 25 Mc./s. which are maintained continuously at Ahmedabad, pronounced fluctuations are sometimes associated with F-scatter in the ionosphere. A dependence of the fluctuations on sidereal time is also observed. Cosmic noise attenuation increases if the F-scatter occurs at an hour of maximum cosmic noise, and decreases if the scatter occurs at the time of minimum cosmic noise. An explanation of the observed effects is offered in terms of the scattering of the cosmic radio waves by spatial variations in electron density. Sporadic E is found to have negligible effect on cosmic noise absorption on 25 Mc./s.