2. Mozambique Channel, Spiral Eddies

This photograph is completely cloud-free and looks down, almost vertically, on the ocean surface in the Mozambique Channel. The eddies, driven by the Agulhas Current, are approximately the same diameter as those in slide #1, but are viewed with the longer-focal-length 250-mm lens. This frame covers an area of approximately 50 kilometers on a side.

This is one of a series of pictures, taken by STS-8 Mission Commander Richard H. Truly, that gave the first indications that spiral eddies might be interconnected. The shear current boundary (the bright parallel lines observed on the ocean surface) is thought to be highlighted by the accumulation of natural surfactants along the shear. These surfactants are natural oils exuded by phytoplankton, and they enhance the reflectivity of the ocean surface.

Oceanographer Paul Scully-Power, who flew on the thirteenth shuttle mission in 1984, observed widespread examples of sea-surface surfactants, suggesting that the concentration of this material worldwide is higher than had previously been thought. Notice that the rotation of the spirals in this view is clockwise, the reverse of that in slide #1. Cyclonic rotation in the southern hemisphere is clockwise, while that in the northern hemisphere is counterclockwise.

STS-8, August-September 1983. Picture #8-42-2090

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