Comparison of Faraday rotation observations at Delhi with IRI model

Comparison of Faraday rotation (FR) observations made at Delhi with FR computed from option II of the International Reference Ionosphere (IRI) shows that during low solar activity (1975–1976) the IRI model grossly overstimates daytime Faraday rotation in all seasons by 185 to 320%. The premidnight and postmidnight values are also overestimated by 130 to 205% and 95 to 200% respectively. During high solar activity (1980), the daytime FR values predicted by the IRI are overestimated by 70 to 110%. The premidnight and postmidnight values are also overestimated by 55 to 115% and 100 to 280% respectively. However, it may be noted that in the 05 to 06 hour time slot, the estimates are within 20% in all seasons during low solar activity and in winter and autumnal equinox of high solar activity. It is suggested that instead of the CCIR set, a different set of co-efficients as applied in option I and II be derived based on the observed data obtained in the low latitude region.