Longitudinal Variability Study of Ionospheric Ranging Errors Around 20 N Geomagnetic Latitude

This study aims to highlight the effect of longitudinal variation on ionospheric ranging errors (IRE) for L1 frequency GPS users along the geomagnetic latitude of 20 degrees north. Observations from 9 GNSS stations - all within ±2 degrees of 200N — have been used, including the newly established GNSS station at Sharjah (SHJ1). The study period was chosen to be the winter solstice of 2018, a minimum solar period. Observation of derived IRE trends shows very small variations at early hours (0500 LT) of the morning. However, the error variation is quite significant at the peak hour (1400 LT) of the day. A comparison with the NeQuick 2 model shows that the model underestimates IRE calculation at 0500 LT and overestimates IRE values at 1400 LT, for most cases. It was also found that the ionosphere at the western hemisphere is generally more active than the eastern hemisphere for both periods. This study shows that the effect of longitudinal variation is significant along near equatorial latitudes and should be considered even at minimum solar periods.