Comparison of E layer critical frequency over the Thai station Chumphon with IRI

Abstract In this research, as a part of working towards improving the IRI over magnetic equatorial region, the critical frequency of E layer in the ionosphere ( fo E) derived from the ionogram at Chumphon station (10.72°N, 99.37°E), Thailand, during 2005–2008 is analyzed. The Chumphon station is located in the magnetic equatorial region at the magnetic latitude of 3.22°N. The seasonal variation of the fo E measurements is compared to the IRI fo E predictions with the optional input in the sunspot number (Rz12) and the solar radio noise flux (F10.7). For a declining phase of the solar cycle 23 during the year 2005–2008, the study shows that the IRI fo E prediction is similar to the fo E observation during the period of 2005–2008. The maximum differences between the IRI fo E prediction and fo E observation are about 500 kHz during daytime period of 2007.