GPS Ionospheric Delay during Extreme Space Weather Conditions in Croatia: A 2003 Halloween Event Case Study

The GPS positioning performance is affected by numerous positioning error causes. The GPS ionospheric delay, caused by various processes known as space weather, appears as the most emphasised single GPS positioning error source. Although the theoretical description of the nature of ionospheric impact on the GPS positioning performance already exists, the GPS positioning performance analysis in various space weather conditions is still to be conducted. The GPS positioning performance in severe space weather conditions is of particular importance, due to abrupt and considerable changes in the vertical ionospheric profile, causing a complex GPS ionospheric delay dynamics. Here the analysis of the maximum GPS ionospheric delay time series taken at the reference station Osijek, Croatia during a marked period of severe space weather conditions in October and November 2003 is presented. After a brief introduction to GPS positioning procedure and space weather, the development of space weather disturbances during the Halloween event is presented. Time series of maximum GPS ionospheric delay at Osijek, Croatia is shown, and its dynamics analysed and compared with the time series of space weather parameters (sunspot number, solar flux and planetary Ap index). Marked correlation between the GPS ionospheric delay and space weather parameters have been observed and presented. Finally, the prospects for deployment of continuous space weather monitoring in forecasting considerable changes in GPS ionospheric delay dynamics have been addressed.