Introduction Geometrical Asymmetry Figure 1 illustrates three cases. The intersection of a cylinder and a plane is a circle if the two are perpendicular, and an ellipse if they are inclined. In fact an air shower cascade disk first grows and then contracts as it passes down through the atmosphere.
Ground level is normally beyond the point of maximum development.
In this conical scenario a series of 2-dimensional isodensity contours in the ground plane are increasingly eccentric ellipses. In reality the structure of an air shower will be more complex. However, as we will see later, an inverted cone seems to be a reasonable first approximation.