Geometry statistics of the 32 shock waves. Panel a: ellipsoid parameter b as a function of ellipsoid parameter a for the 32 events. The colours correspond to the solar activity of the event day, with, from yellow to red, the smallest to the largest number of sunspots observed. The red points are the average b/a ratio for each event. The purple dashed line corresponds to the overall ⟨b/a⟩ ratio, i.e. b = 1.02 × a and the black dashed line to a case where b = a. Panel b: in two parts. Top: histogram of ⟨b/a⟩ ratio. Bottom: boxplot of ⟨b/a⟩ ratio. On the purple box, the central mark indicates the median, whereas the bottom and top edges indicate the 25th and 75th percentiles, respectively. The whiskers extend in red to the most extreme data points, and in dot blue are plotted individual data points considered outliers. Panel c: mean width of the shock wave, ⟨2b⟩, as a function of V_R, max, the maximum radial speed of the shock wave.