Stunning “Sunshine” Turns Sea Surface Into A Swirling Silver Mirror
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An astronaut from the International Space Station (ISS) recently took a stunning photograph of a “sunshine” that turned the surface of the sea into a swirling silver mirror surrounding a pair of Greek islands. The phenomenon of color change, caused by the SunLight from reflecting off the still sea directly into the astronaut’s camera, highlights interesting oceanographic effects on and below the surface of the water.
An unidentified Expedition 67 crew member captured the image on June 25 using a digital camera pointed from an ISS window. The largest landmass at the heart of the photo is Milos, a 58 square mile (151 square kilometer) Greek. volcanic island, and its smaller uninhabited partner to the west is Antimilos, which measures about 3 square miles (8 square km). The silver seas surrounding the islands are the Sea of Myrto to the northwest of Milos and the Sea of Crete to the southwest, both of which are part of the larger Mediterranean Sea. The image was posted online on September 12 by NASA Earth Observatory.
Sunglare can be seen by observers in space when sunlight reflects off particularly calm seas or other flat bodies of water with little or no wave action. It resembles the way light reflects off a still sea during sunrise or sunset as seen from Earth, causing a bright streak across the surface; but from space the contrail looks like a massive silver smudge, often covering several hundred square miles, and appears to be moving across the ocean like Earth turned.
The wavy lines and swirls in the image, which cut across the silver surface of the sea like scratches on a mirror, are caused by wind-driven surface currents and sea currents deeper below the surface, as well as by rarer phenomena, such as internal waves moving below. the surface of the water and the gyres – large systems of rotating ocean currents. Most of these features would normally go unnoticed from space, but because they scatter some of the sunlight, the features become glaring in solar reflection.
Related: Landsat satellites: 12 amazing images of the Earth from space
One of the most striking oceanographic features in the image is a vortex-like whirlpool located east of Milos, which almost looks like a huge whirlpool from above. However, rather than pulling things like a whirlpool, these swirling sheets of water play an important role in maintaining nearby currents that circulate nutrients in the ocean, according to the National Oceanic and Atmospheric Administration (NOAA) (opens in a new tab).
Another remarkable feature is the long straight line in the lower left of the image, which is most likely the wake of a ship moving at high speed on the surface, according to NASA’s Earth Observatory.
But perhaps the most interesting feature of the photo is the rather innocuous set of parallel lines off the northeast coast of Antimilos. These lines, which are mostly obscured by the clouds surrounding the island, are “internal waves” – massive vertical waves that cut through the water below the surface. Unlike surface waves, which are mainly driven by ocean currents or strong winds, internal waves are the result of gravity waves (not to be confused with gravitational waves in space-time).
Gravity waves cross the interface, or meeting points, of two fluid media after gravity upsets the balance between the two, which in this case is caused by the earth’s tides. The seas are stratified, that is to say made up of layers of water of different densities due to variations in temperature and salinity. Gravity waves can therefore form where these layers meet, creating internal waves in the ocean, according to The conversation (opens in a new tab).
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Normally, internal waves pass through water without leaving a visible trace. But the sun’s glare provides the contrast needed to illuminate the waves hidden beneath the surface. Other images of sun flare captured by astronauts and satellites can also highlight atmospheric gravity waves that occasionally form where the atmosphere and ocean surface meet, creating massive ripples. As a result, scientists commonly use solar glare to study gravity waves above and below the surface, according to The Conversation.
Researchers also use images of sun flare to track oil spills because oil slicks on the ocean surface reflect less light than water, according to NOAA.
However, for other marine scientists who rely on satellite images to track algal blooms or monitor ocean color, sun glare can be a nuisance. As a result, these scientists often have to remove sun flare from their satellite images, according to NOAA.
Originally posted on Live Science.