Modelling the probability of ionospheric irregularity occurrence over African low latitude region

Abstract

This study presents models of geomagnetically quiet time probability of occurrence of ionospheric irregularities over the African low latitude region. GNSS-derived ionospheric total electron content data from Mbarara, Uganda(0.60°S, 30.74°E, geographic,10.22°S, magnetic) and Libreville, Gabon(0.35°N, 9.68°E, geographic,8.05°S, magnetic) during the period 2001–2012 were used. First, we established the rate of change of total electron content index (ROTI) value associated with background ionospheric irregularity over the region. This was done by analyzing GNSS carrier-phases at L-band frequenciesL1and L2 with the aim of identifying cycle’s lip events associated with ionospheric irregularities. We identified at both stations a total of 699 events of cycle slips. The corresponding median ROTI value at the epochs of the cycles lip events was 0.54TECU/min. The probability of occurrence of ionospheric irregularities associated with ROTI0.5TECU/min ≥ was then modelled by fitting cubic B-splines to the data. The aspects the model captured included diurnal, seasonal, and solar flux dependence pattern soft the probability of occurrence of ionospheric irregularities. The model developed over Mbarara was validated with data over Mt. Baker, Uganda(0.35°N, 29.90°E, geographic,9.25°S, magnetic), Kigali, Rwanda(1.94°S, 30.09°E, geographic,11.62°S, magnetic), and Kampala, Uganda(0.34°N, 32.60°E, geographic,9.29°S, magnetic). For the period validated at Mt.Baker (approximately, 137.64km, northwest), Kigali (approximately, 162.42km, southwest), and Kampala (approximately, 237.61km, northeast) the percentages of the number of errors (difference between the observed and the modelled probability of occurrence of ionospheric irregularity) lessthan0.05are97.3, 89.4, and81.3, respectively.