Secondary circulation
In fluid dynamics, a secondary circulation is a weak circulation that plays a key maintenance role in sustaining a stronger primary circulation that contains most of the kinetic energy and inertia of a flow. For example, a , but their evolution and maintenance against friction involves an in-up-out flow that is important to its clouds and rain. On a planetary scale, Earth's winds are mostly east-west or zonal, but that flow is maintained against friction by the Coriolis force acting on a small north-south or meridional secondary circulation.
