The minimum frequency at which echoes are observed in vertical incidence soundings, fmin is dependent, amongst other terms, on the absorption present in the ionosphere and thus can be used as an absorption index. In practice, it is particularly useful to discover the large changes in absorption with time and position. For comparison of daytime fmin at Multan (30.20N, 71.50E) during Solar Minimum (1996) and Solar Maximum (2000) years, the seasonal and annual means of monthly medians of fmin are used for the study. For determining fmin the ionograms recorded at Multan by Panoramic Ionospheric Recorder-9 (PIR-9) have been used. |
Abstracts 
