An essential element of convection and MHD dynamos, more familiar examples of this quantity occur in hurricanes and airflow around airplane wings.  
Kelvin's circulation theorem guarantees that in an inviscid, incompressible fluid, this quantity, the curl of the velocity vector, is constant.  An essential element of convection and MHD dynamos, more familiar examples of this quantity occur in hurricanes and airflow around airplane wings.  For ten points, name this quantity, the amount of rotation in a fluid flow.
Kelvin's circulation theorem guarantees that in an inviscid, incompressible fluid, this quantity, the curl of the velocity vector, is constant.  
vorticity