Fluid Flow

The wind and the general flow of air and ocean currents around our planet is of great importance to aviators and sailors alike. It is often hard to visualise exactly what is going on. Satellite pictures can show us a lot, not only for illustrating the weather forecasts we all see on TV, but sometimes also for helping us to visualise what is happening.
I was looking through a few satellite pictures recently and was struck by how similar fluid flow looks in different scales, whether it is in the atmosphere or in the oceans. We are all used to looking at the water in rivers and streams and seeing all the little eddies but we are not so familiar with what happens on a larger scale.
The first four satellite photos below show what is happening in the sea. In the first two the swirling currents are made visible by the plankton in the water, and in the second two by the drifting ice. For those of us who sail, it explains the odd changes of current a boat can be subjected to despite what the tide tables say.


The US Geological Survey has put together several collections called Earth As Art. They feature Landsat satellite images selected for their artistic quality, rather than for scientific reasons. The Landsat programme is a series of Earth-observing satellite missions jointly managed by NASA and the US Geological Survey. Since 1972, Landsat satellites have collected information about Earth from space. The images are presented in “false colour” – satellites use both visible and invisible parts of the electromagnetic spectrum. Near-infrared light is invisible to the human eye, but adding it to these images allows scientists to “see” the surface of the Earth in other than natural colours.
In the style of Van Gogh’s painting “Starry Night,” massive congregations of greenish phytoplankton swirl in the dark water around Gotland, a Swedish island in the Baltic Sea. Phytoplankton are microscopic marine plants that form the first link in nearly all ocean food chains. Population explosions, or blooms, of phytoplankton, like the one shown here, occur when deep currents bring nutrients up to sunlit surface waters, fuelling the growth and reproduction of these tiny plants.

Electric blue-coloured plankton blooms swirl in the North Atlantic ocean off Ireland. Plankton, the most abundant type of life found in the ocean, are microscopic marine plants that drift on or near the surface of the sea. While individually microscopic, the chlorophyll they use for photosynthesis collectively tints the surrounding ocean waters, providing a means of detecting these tiny organisms from space with dedicated ‘ocean colour’ sensors.

Like distant galaxies amid clouds of interstellar dust, chunks of sea ice drift through graceful swirls of ice in the frigid waters of Foxe Basin near Baffin Island in the Canadian Arctic.

Along the south-eastern coast of Greenland, an intricate network of fjords funnels glacial ice to the Atlantic Ocean. During the summer season, newly calved icebergs join slabs of sea ice and older weathered bergs in an offshore slurry that the southward-flowing East Greenland Current sometimes swirls into stunning shapes. Exposed rock of mountain peaks, tinted red in this image, hints at a hidden landscape.
But what is also interesting is that the same patterns can be found on a much smaller scale in a flame…

This image of a flame struggling for existence milliseconds before it is snuffed out by a blast of cold air has won a scientist a top award. It is the winning image in the Engineering photo competition at the University of Cambridge and was taken as part of a research project into the physics of flame extinction. Dr Rob Gordon, a Royal Society Newton International Fellow, was examining flame structures to prevent aircraft jet engines losing power due to flames suddenly going out. The photograph was taken using two high-speed cameras working at 5000 frames per second.
And for those of us who fly, the atmosphere is where we work, move and have our being. We are all used to the patterns created by fontal depressions that sweep across the temperate latitudes as seen in these pictures of the Earth.

Severe storm in California as seen from space. 

But have you ever seen pictures of the vortices found downwind of island peaks and mountains?

Creating a striking design which looks a bit like a serpent swimming through clouds, curling patterns of eddies are formed as air flows around and over the island of Tristan de Cunha in the South Atlantic. These spiraling cloud patterns, caused when prevailing ocean winds encounter an island, are known as von Karman vortices or ‘vortex streets’. Home to about 275 people, Tristan de Cunha is considered to be the most remote inhabited island in the world, lying 2,816km (1,750 miles) from South Africa, the nearest land, and 3,360km from South America.

The steady south, southwest flow of bright white clouds on the Portuguese trade winds is dramatically interrupted by the island of Maderia and by the Canary Islands, resulting in swirls and eddies on the leeward side of each island. In the northeast corner of the image, the island of Maderia, Portugal, rises 1,862 meters (6,109 feet) above the ocean surface. On the day this image was captured, large fires were burning on the island and a wide plume of gray smoke can be seen trailing from the island.
Back on Earth, we poor souls, at the mercy of the elements, just see it all as chaotic weather, rain, winds, snow and turbulence. And when at sea, the unexpected ocean currents that set us towards the rocks.
Pictures from NASA and University of Cambridge