Looking into the Karman Vortex

With amazing missions observing Mars, Venus and the Saturn system, itis all too easy to forget that the Earth has some pretty amazing features tosee too. Chris Brooke sent me a link to his blogpost about the 30 Most Incredible Abstract Satellite Images of Earth. The images Chris uses were part of a NASA exhibitiontitled Earth As Art which showcases amazing landscape, seascape and atmospheric patterns seen by Landsat 7. I recognise a few of them but as always there are some new ones I haven'tseen before.

These vortices appeared over Alexander Selkirk Island in the southern Pacific Ocean. Landsat 7 WRS Path 6 Row 83, center: -33.18, -79.99 CREDIT: USGS/NASA

Given my fascination with clouds - they always get in the way of observing the night sky (and sometimes the day if you observe at 30 GHz) - I thought I would show a Von Karman Vortex Street. These vortices were caused by the unsteady separation of air flow over Alexander Selkirk Island in the southern Pacific. As I've shown it here, the wind would be heading towards the right. To observe the effect you need the correct ratio of the speed of the flowing fluid - in this case the atmosphere - to the viscosity of the liquid. Basically this causes eddies to form from each side of the obstructing object in turn. As a result, the eddies also have opposite rotations. As they move further away from the obstruction they disappate their energy through friction and gradually disperse.

The Earth as Art site has more examples of pretty Karman Vortices.