The Juan Fernández Islands' vortex streets
The Juan Fernández Islands lie in the Pacific about 670 km off the coast of Chile. Alejandro Selkirk is the westernmost; Robinson Crusoe Island lies east of it.
What the satellite saw
NASA's Aqua satellite photographed them with MODIS on 2 February 2019, a street behind each island (Earth Observatory, "Love is in the Air", for the heart shapes the swirls drew). The swirls are in a layer of marine stratocumulus.
Why these islands
Height. Alejandro Selkirk rises 1,268 m above the sea. NASA's rule: an island must be tall enough to force the air around it rather than over it.
A steady wind low in the atmosphere, which, NASA notes, is why the spirals so often form behind islands in the path of the trade winds.
Two bodies. Each island sheds its own street; in the tunnel, try Draw and raise a second island beside the first.
Make it in Wind Tunnel
- Open the link below, or press Juan Fernández under Island: the wind starts from 225°, south-west.
- Press Cloud under Look and Satellite under Colour: white cloud on a blue-grey sea, as the photo sees it.
- Turn on Satellite photo under Island to lay this photo over the corner of the frame, beside the flow.
- Choose 4K and 20 seconds under Save, and press MP4 once the street has formed.