The scintillation receiver takes 50 GPS measurements per second, and performs statistical analysis on these measurements. These statistics are shown below. The S4 index (top) is a measure of amplitude scintillation, that is rapid variation in the apparent signal strength. Sigma phi (bottom) is a measure of phase scintillation, that is (roughly speaking) rapid oscillation in the delay between the signal leaving the satellite and arriving at the receiver.
Link to graph at current time.