Figure 3. The time dependence of the "vertical'' TEC I(t) value at the AZU1 Site of the Californian regional GPS network, corresponding to different time intervals: A (day, a) and B (night, e), marked in Figure 4c; TEC variations dI(t) filtered in the period range of 32-128 minutes (b, f), of 10-25 minutes (c, g), and 2-10 minutes (d, h). Given above the curves are the recording dates and the PRN numbers. The scale of local time is for the longitude of 240oE.