The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Terra satellite passed over the North Pacific Ocean on April 20, 2013, and captured a true-color image of a complex cloud cover. Some of the cloud patterns are formed by wind interacting with Alaska’s Aleutian Islands, and other patterns are the result of pollution.
In the northeast section of the image, “V” shaped waves can be seen stretching southeast across the ocean. These are ship-wave-shaped wave clouds, and are formed as the moving air hits the tall volcanic peaks of the Aleutian Islands. When the fast moving winds hit the tall, immobile peaks, turbulence is created. The air can be forced to pass in sinuous waves, with both peaks and troughs forming on the lee side of the islands. At the peak of the waves, clouds form, while at the troughs, clouds dissipate and the sky is clear. This particular pattern looks like the wave-shaped wake behind a ship, hence the name.
Near the center of the image, a long swirling pattern can be seen off the leeward side of an island, with another, fainter swirling pattern to the west. These are von Karman vortex streets, and are another pattern created by turbulent wind passing a tall peak. The different patterns are created by the shape of the islands. Von Karman vortex streets are created when the shape of the “bluff body” interfering with wind flow is just about as wide as it is tall.
Further south, bright linear but irregular streaks can be seen. These are ship tracks, and are created by particles and gases released from ships traveling the ocean below. The aerosols can act as cloud seeds, and when conditions are right, accumulate water molecules, forming the tell-tale clouds that mimic the trail of the vessels’ voyage as it travels across the ocean below.