Distributions of the properties of the base brightenings selected with the visual identification method (50 base brightenings). (a) shows the mean intensity of the base brightenings without subtracting the local background while (b) shows the mean intensity with the local background removed. (c) – (f) show the lifetime, area, length-to-width ratio, and velocity. The velocity here is a projection on the PoS and is calculated using the first and last positions of the intensity-weighted center of the base brightening.