This is the flow as it evolves in time. Notice how the particles, which follow the trajectories at each moment in time, trace out cycloidal patterns and look nothing like the streamlines. Although at a given instant, streamlines and trajectories are both tangent to the velocity vectors, trajectories may deviate significantly from the streamlines over even a short time interval.

The MATLAB source code for these animations can be found here and uses a subroutine written by Zhenhai Wang.

• Durran, D.R., 1999: Numerical Methods for Wave Equations in Geophysical Fluid Dynamics, Springer, 465pp. (Referenced for the second order Runge-Kutta scheme used to create the trajectories)
• Kundu, P.K. and I.M. Cohen, 2002: Fluid Mechanics, Academic Press, 730pp.
• Young, D.F, B.R. Munson, and T.H. Okiishi, 2001: A Brief Introduction to Fluid Mechanics, John Wiley, 517pp.

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