183-187Ionospheric absorption has been studied in model ionospheric layers at Waltair using Sen-Wyller's fully generalized magneto-ionic theory. On the basis of numerical calculations a suitable model is selected that gives values of absorption, virtual height and the cos index n in reasonable agreement with the experimentally observed values from Al absorption data. It is found that 'the assumption of a single Chapman layer model along with an exponential collision frequency profile leads to a cos index less than 1.5In particular. a three-tier model of electron density profile consisting of (i) a Chapman type E(Ne0 = 2 x 105 cm-3 and h0 = 110 km) and a Chapman type D(N e0= 103 cm-3 and h0= 75 km); (ii) a constant electron density lower D-region (Ne= 200 cm-3 in the height range 50-70 km) with a uniform scale height of 6 km, and (iii) an exponential collision frequency profile assuming the value of v0 -= 2 X 104 sec-1 at 110 km, is proposed
