Sketch of a longitudinal cut along the axis of a coronal loop harboring a fundamental standing slow body sausage mode, at the velocity’s maximal amplitude (left) and the local cartesian model at the boundary (right). The arrows on the left represent the velocity field and their lengths are to scale with the relative local magnitude of the field for a slow body sausage mode at a given time. The lengths and directions of the magnetic field arrows on the right figure are consistent for that same slow mode, whereas for the velocity arrows only the direction is consistent (the length of the exterior velocity arrow having been increased for visual clarification).