Impacts of the December 2006 solar radio bursts on the performance of GPS

Four X class solar flares originated from active sunspot region 10930 on 5, 6, 13, and 14 December 2006. Wideband noise from associated solar radio bursts (SRB) on 6, 13, and 14 December drastically reduced the carrier-to-noise ratio (C/No) of the Global Positioning System (GPS) signals. Using specialized high-rate GPS receivers from the AFRL-SCINDA global network, we investigate the impacts of these SRBs on the performance of GPS and quantify the Sudden Increases in Total Electron Content (SITEC) caused by the solar flares. The C/No reduction experienced by a GPS receiver during a SRB depends on the solar incidence angle due to the anisotropy of the antenna gain. We derive an expression for the vertical equivalent C/No reduction due to a SRB in order to compare measurements collected at locations where the solar incidence angles differ. During the SRB on 6 December we observed C/No reductions exceeding 25 dB, intermittent loss of lock, and complete loss of GPS positioning information lasting for several minutes. Peak positioning errors in the horizontal and vertical directions reached 20 and 60 m, respectively. While deep C/No reductions were observed during the SRBs on 6, 13, and 14 December, only the 6 December event was strong enough to substantially degrade GPS tracking and positioning accuracy.