21. In this case the Navier Stokes equations reduce to the vorticity -transport equations. 22. Using this in the vorticity transport equation, Rayleigh's equation is obtained. 23. But attributing causation to the vorticity in this way is not consistent with the physics. 24. Curl to find an equation for vorticity . 25. As usual for the vorticity dynamics, the pressure drops out of the vorticity equation. 26. As usual for the vorticity dynamics, the pressure drops out of the vorticity equation. 27. The first assumption will be an initial potential vorticity anomaly somewhere in the upper troposphere. 28. The flow field associated with the trochoidal wave is not irrotational : it has vorticity . 29. Instability is caused when the vortex tube, the line of concentrated vorticity , is displaced. 30. The enstrophy can be described as the integral of the square of the vorticity \ omega,
