Alejandro Selkirk Island Von Karman vortex street
 

Dear all,

I'm trying to determine the velocity of the coulds that made a Von Karman vortex
street near Juan Fernandez Islands:
http://earthobservatory.nasa.gov/IOTD/view.php?id=625

A Von Karman vortex street occures for:
Re = 90

Alejandro Selkirk Island diameter is:
D = 1500 meters

The air kinematic viscosity is:
nu_air = 15.6E-06 meters**2 / second

The relation is:
Re = Velociy_clouds * D_vortex / nu_air

So:
Velocity_clouds = Re * nu_air / D_vortex
= 2.8E-07 meters / second
= 1 meter / 12 days


Cloud velocity is 1 meter / 12 days, really?

Why pick a Reynolds number of 90? A vortex street can exist for a wide range of Reynolds numbers.