Dynamic pipe effect

dynamic pipe effect (DPE)

A model of tornado formation in which the incipient tornado vortex builds downward from aloft owing to the effects of radial convergence of angular momentum at progressively lower heights.

Initially, there is a strong mesocyclone aloft within a convective storm. The incipient tornado vortex that forms within the mesocyclone is assumed to be in cyclostrophic balance, such that the elevated rotating column of air behaves like a “dynamic pipe.” Low pressure is present within the dynamic pipe owing to the vertical vorticity of the air within the pipe. Thus, an upward-directed vertical pressure-gradient force exists beneath the dynamic pipe, which accelerates air upward. The radial acceleration that accompanies the upward acceleration draws angular momentum, if present, inward beneath the dynamic pipe, increasing vertical vorticity beneath the pipe via convergence and stretching until cyclostrophic balance is achieved, which extends the base of the dynamic pipe downward. For tornado formation to occur in this model, subsequent inward and upward accelerations beneath the dynamic pipe must continue to draw angular momentum inward at progressively lower altitudes, thereby extending the dynamic pipe toward the surface. The dynamic pipe also grows upward in time owing to the upward advection of vertical vorticity. The latest tornado research findings as of 2013 suggest that the DPE is largely theoretical and likely not a dynamic process through which tornadoes commonly form, if at all, in the real atmosphere.

A cyclonically rotating vortex, around 2–10 km in diameter, in a convective storm.

1. A type of stress characterized by uniformity in all directions.