Ionospheric Absorption on 2.5 MHz at Ahmedabad

Abstract

A study is made of diurnal and day-to-day variations of ionospheric absorption on 2·5 MHz measured by Al method at Ahmedabad (23 ^oN, 72·6 °E; magnetic dip 34 °N) for the year 1973. It is shown that the diurnal variation of absorption follows a law <i>L=L₀ </i> cos<i>ⁿ</i> <img src='/image/spc_char/lembda.gif' border=0> where <i>L₀ </i>is absorption when the sun is at zenith. The value of the index <i>n </i> is found to vary from 0·4 to 1·05 during the course of a year, its yearly mean value turning out to be 0·70. The maximum of absorption occurs a little later than noon, the delay being about 45 min in winter and about 12 min in summer. Among the day-to-day variations, the increases in absorption are related to the increases in 1-8 Å solar X -ray flux and the decreases to the occurrences of a reflecting low-type sporadic-E layer. The results are discussed in the context of the roles played by the D- and E- layer ionizations and the atmospheric composition.