Effect of electron-ion collisions in theFregion of the ionosphere on the absorption of cosmic radio noise at 25 Mc/s at Ahmedabad changes in absorption associated with magnetic storms

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Measurements of cosmic radio noise at 25 Mc/s, being made at the Physical Research Laboratory, Ahmedabad, since March 1957, have shown much larger values of absorption than those observed by Shain and Mitra in Australia. This fact, together with the empirically known dependence of the absorption on the critical frequency of the F region, and the effect of magnetic storms on the absorption found from the Ahmedabad observations have led us to examine the different possible parameters that may affect cosmic-noise absorption. It is found that electron-ion collisions in the F region both below and above the level of maximum electron density contribute in a substantial way to the absorption of cosmic radio noise. The values of hourly absorption due to collisions of electrons with neutral particles and with ions have been calculated for a period of 6 days in August–September 1957, when there were three magnetic storms. The results obtained show a depletion of electrons above F maximum on the day following the commencement of the magnetic storm and a refilling on later days. The results are discussed in relation to findings from satellite observations about particle fluxes in the Van Allen belts during magnetic storms.