Ship-wave-shape wave clouds in the North Sea
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Ship-wave-shape wave clouds in the North Sea

November 16, 2011
From space, the clouds over the North Sea can appear much like artfully etched glass, with geometric designs intertwining in a complex, frosted pattern. Instead of being created by abrasion or caustic acid on clear glass, however, these designs are created by the interaction of wind and mountains on a layer of cloud. The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Aqua satellite captured this true-color image of ship-wave-shaped-wave clouds over the North Sea on November 9, 2011.

The peaks on the Shetland Islands (center right) have distinct ship-wave-shaped wave clouds forming on the lee side of the islands. The clouds on the lee side of the Orkney Islands, the northern tip of Scotland (southern land mass), the Faroe islands (upper left) are also similarly sculpted by moving winds.

These three dimensional wave patterns develop with air flows over an isolated peak, or a very short length of ridge. They most commonly form when there is a layer of stratocumulus cloud under an inversion which is not far above the mountain peak. As the wind blows across a single peak, the air is disturbed and the pattern caused by the wind motion looks much like the wake left behind a ship as it travels across the ocean. The same conditions can also cause parallel wave bars, especially when multiple mountain peaks string together along a ridge. These lee waves, as they called, are part of the pattern off the Faroe Islands. Where different wave patterns interact, complex and intricate patterns are formed.

The relatively low layer of cloud which is decorated by waves appears a faint blue color in this image. High altitude cirrus clouds appear bright white, and cast shadows on the clouds below.

Credits: Jeff Schmaltz, MODIS Land Rapid Response Team, NASA GSFC

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