Variation in PCW activities during three SIR phases with the solar cycle. (a) Time series of the daily sunspot number. (b) Time series of the Mars solar longitude (L_S, a measure of the season on Mars), which repeats itself from one MY to another. (c, d) PCW occurrence rate and median wave amplitude as a function of time, with the green, red, and black points corresponding to the pre-SIR, SIR, and post-SIR phases. The gray-shaded regions correspond to the perihelion season (L_s = 180º−360º) of MYs 32–35.