Variation of ionosonde foE and its comparison with IRI-2016 & a local model over Pakistan longitude sector during solar cycle 22

The study presents the variation of ionospheric critical frequency of E-layer ( foE ), its comparison with International Reference Ionosphere (IRI-2016) over Pakistan and suggests an artificial neural network (ANN) based algorithm to predict noontime daily hourly values. The ionosonde measurements of Karachi (Geog. Coord: 24.95 ° N, 67.13 ° E, dip latitude = 17.0 ° N), Multan (30.18 ° N, 71.48 ° E, 21.8 ° N) and Islamabad (33.75 ° N, 73.13 ° E, 25.2 ° N) have been used for the purpose. The observed foE values have been analysed during the high, moderate and low solar activity years 1989, 1992 and 1996, respectively. Results show a strong correlation between foE and solar activity which was expected because the E-layer is essentially solar controlled. It is found that foE peaks around noon with higher values during summer. The annual relative percentage deviation between data and IRI-2016 modelled values remains less than 6% for all locations and years under study. The ANN based algorithm predicts daily noontime foE values with a goodness of fit of 78%, compared to the IRI-2016 prediction, which has a goodness of fit of 71%. It is noted that the performance of IRI-2016 in predicting monthly hourly median values of foE improves with decreasing solar activity. The study confirms the data authenticity of foE over Pakistan and suggests an ANN based algorithm in predicting noontime values with no immediate updates to IRI-2016 for this Asian longitude sector.