119-124Multifrequency ionospheric AI-absorption data obtained at Ahmedabad (23°N, 72.6°E, mag. dip 34°N) are analyzed to study the frequency dependence of absorption for low and high solar activity epochs, and also for low and moderately high solar activity years (1976 and 1978).The exponent m in the inverse frequency dependence of measured absorption is determined for practical purposes. The diurnal variation of the index m for different months and its seasonal variation at a fixed solar zenith angle (SZA) are studied for total absorption (Ltotal) as well as for its non-deviative (Lnd) part. It is found that (Ltotal) does not obey the inverse frequency square law. During sunspot minimum, m is found to vary with time of the day showing maximum (annual average =0.71) around noon and falling towards morning and evening hours, whereas for sunspot number Rz = 100, it shows the opposite trend showing minimum (average value =0.60) around noon and increasing towards morning and evening hours. In the case of non-deviative (Lnd) absorption. the index m in 1976 and 1978behaves in a manner similar to that of Ltotal for Rz =00 and 100, but m for Lnd has higher values and range of variation, the values being clustered around the theoretical value 2 near noon, in the spring months of 1976and for most part of the day in August 1978. These results suggest that the higher value of m on the average for Ltotal during increased solar activity is due to major contribution of non-deviative absorption and only small contribution of deviative absorption to the total absorption during high solar activity. It is also verified that the value of the proportionality constant A in the assumed frequency dependence law of total absorption changes with the or SZA corresponding to the changes in the value of m
