Fig. 10

CDFs of the daily TEC occurrence estimated with Method II. The occurrence rate, which is the number of days per 100 years, and the occurrence rate in percentage are shown on the left- and right-hand axes of the ordinate, respectively. The black histograms are derived from the average slab thickness shown in Fig. 9. The blue and red histograms are derived with slab thicknesses of average + 3σ and + 4.2σ, which are shown with blue and red vertical lines, respectively. The solid, dotted, and dashed horizontal lines represent occurrence rates of 0.3%, 0.03%, and 0.003%, which correspond to frequencies of once per year, 10 years, and 100 years, respectively