The performance of IRI-2016 in the African sector of equatorial ionosphere for different geomagnetic conditions and time scales

Abstract

This paper presents the performance of IRI-2016 model in describing the East African sector of equatorial ionosphere during different geomagnetic conditions and time scales. The analysis is carried out by taking six years (2008 and 2011–2015) of the vertical total electron content (vTEC) data from GPS receiver located at Arba Minch (Geographic: 6.06°N and 37.56°E; Geomagnetic: −3.03°N and 109.29°E) in Ethiopia. The IRI-2016 model either underestimates or overestimates observations depending on time of day, months, season, solar and geomagnetic conditions. An underestimation becomes more pronounced from the first to third quartiles, while an overestimation is nearly constant. The diurnal variation pattern of measured vTEC (vTECo) shows a single peak mostly occurring between 1000 and 1400 UT (1230 and 1630 LT), while the modeled vTEC (vTECm) is characterized by two remarkable peak values with the first peak occurring between 0500 and 0700 UT (0730 and 0930 LT), and the second peak occurring between 1300 and 1400 UT (1530 and 16300 LT). The nighttime monthly peak vTECm is lower compared to observations during 2008, but it is reversed during 2011–2015. Seasonally, the vTECo variations show a semiannual variation pattern with maximum values during March equinox and December solstice months and minimum during June solstice and September equinox months. This trend equally explains the semiannual variability noted on the seasonal percentage deviation in vTECm variability. The mean and median annual observations show better agreement with vTECm during daytime, but opposite at nighttime hours (except in 2008). The response of the equatorial ionosphere for storm, which was observed clearly in the observations, did not show in the model results. The vTECo shows a significant relation with both merging and interplanetary electric fields during storm. This suggests that a linkage of those parameters with storm-time vTEC needs to be established for a variety of geophysical conditions to improve the forecasting capability of the model. Generally, the IRI-2016 model shows better agreement with observations during solar minimum compared to other solar activity phases. We suggest that the results from this study would complement in the model improvement towards near real time predictions of different ionospheric parameters over the equatorial and low latitude regions like East Africa.