Comparison of maximum usable frequency (MUF) variability over Peninsular Malaysia with IRI model during the rise of solar cycle 24

• Variability of MUF test has been compared with MUF from IRI model.
• Variability MUF IRI is higher than the MUF test but both magnitudes are similar.
• MUF is more vulnerable to variability during the nighttime than the daytime.
• Variability range during the daytime is nearly half compared to the nighttime range.
• Increasing in sunspot number causes a decreasing of MUF variability.

The aim of this paper is to study maximum usable frequency (MUF) variability over Peninsular Malaysia (112.5°E, 2.5°N) which is located in the equatorial region during the rise of Solar Cycle 24 (2009–2011). The MUF Test data was obtained from high frequency (HF) transmission tests that were conducted from April 2009 to September 2011. Relative variability VR was used to compute the relative variability of MUF. Variability of diurnal, seasonal and sunspot effect on MUF of test was compared to International Reference Ionosphere (IRI) version of 2012. The results show that: (a) MUF from the IRI model is higher than the MUF Test but the magnitude for the MUF Test and IRI are similar; (b) from the diurnal analysis, MUF is more vulnerable to variability during the nighttime than the daytime where the variability range for MUF Test and IRI during daytime is 4–12% compared to the nighttime range of 10–30%; (c) seasonal variability for MUF Test in 2011 indicates no clear trend for all seasons, and the seasonal and monthly variability for both MUF VR in 2011 is lower compared to 2009 and 2010; and (d) when sunspot number increases, MUF VR decreases. This result complements the variability in the equatorial and low latitude regions in that when solar activity increases, variability decreases.