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Obstacles of any kind can set up such vortices—known technically as a Von Karman vortex street—from islands to craters to chimneys. The size of each swirl can be judged from the length of the island. Under ideal conditions, clouds make the swirls visible. However, a vortex street will only form under certain conditions of air speed, atmospheric stability, and obstacle size. Conditions are ideal for production of vortex streets in the vicinity of Guadalupe Island, which is known to produce them almost every day in June, July and August. The phenomenon is named after Theodore von Karman, a Hungarian-American engineer and fluid mechanics expert.
Also visible at image top right is a series of parallel cloud lines. Known colloquially as “gravity waves,” these are ripples at the boundary between atmospheric layers of slightly different density. The same phenomena was recently observed by astronauts onboard the International Space Station while flying over the Great Lakes.
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Lake Ontario—like the Great Lakes Erie, Huron, and Superior—is roughly divided between the United States and Canada. The USA side of Lake Ontario has its shoreline in the state of New York, while its Canadian shoreline lies within the province of Ontario. The city of Kingston, Ontario, is visible near the Saint Lawrence River outflow from the lake. Several other landscape features of New York State are visible in the image, including the Finger Lakes region to the west of Syracuse. To the northeast of Syracuse, the dark wooded slopes of the Adirondack Mountains are visible at image upper left. Patchy white cloud cover obscures much of the land surface to the west of Lake Ontario.
The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured an image of the whiting event on the same day, August 24, 2013.
Editor’s Note: A previous version of this story identified the discoloration of the water as a bloom of phytoplankton or harmful algae. Such events can produce stunning color changes, as shown here. However, scientists working on the water in the area provided information to verify that it was instead a whiting event.
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A small, vegetated island and shallow sand bars of the Great Sandy Strait are visible in this astronaut photograph from the International Space Station. A small, bright white exposure of sand is visible above the water level near the center of the image, while submerged sands appear as flowing, bright blue ribbons.
Hervey Bay was once a major freighting center for the sugar cane industry, but now the local economy is largely based on tourism, with whale watching a popular attraction. The estuary provides habitat for breeding fish, crustaceans, turtles, and other sea life, as well as a wide variety of birds—including wading species such as Eastern Curlews, Bat-tailed Godwits, and Pied Oystercatchers. Nearby Fraser Island is the world’s largest sand island and a World Heritage site.
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This image was taken about 15 minutes after local midnight in early August 2013. From their vantage point at 222 kilometers altitude, the astronauts were able to look northeast and see a near-midnight sunrise (when it was approaching noon in England). The rising Sun makes a red, teardrop-shaped reflection in the lower center of the image—perhaps a reflection within the camera lens, from the window frame, or from some item inside the spacecraft.
Long, blue-white ripples appear in the atmosphere above the midnight sun. These are noctilucent or “night-shining” clouds. Some astronauts say these wispy, iridescent clouds are the most beautiful phenomena they see from orbit. Noctilucent clouds are best seen after sunset, when the viewer is on the night side of the day-night line and these high clouds are still lit by the Sun. Crews are trained in this somewhat complicated geometry of clouds being lit from beneath, the spacecraft in sunlight, and the ground below in darkness.
Noctilucent clouds are also known as polar mesospheric clouds (PMCs), as they appear in the summer hemisphere over polar latitudes. Some data suggest that these clouds are becoming brighter and appearing at lower latitudes, perhaps as an effect of global warming. A comparison of noctilucent cloud formation from 2012 and 2013 has been compiled using data from NASA’s Aeronomy of Ice in the Mesosphere (AIM) spacecraft. You can see the sequence here.
Polar mesospheric clouds are interesting because they form much higher in the atmosphere (75 to 90 kilometers) than the normal rainclouds that form in the lowest, densest, “weather-layer” below 15 kilometers. The weather layer, or troposphere, appears in this image as a thin, orange line along the left horizon.
Other astronaut images of PMCs:
NASA Earth
Observatory (2010, July 5) Polar
Mesospheric Clouds Illuminated by Orbital Sunrise.
NASA Earth
Observatory (2010, February 22) Polar
Mesospheric Clouds, Southern Hemisphere.
NASA Earth
Observatory (2003, August 10) Noctilucent
Clouds.
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While much of the country is lightly populated desert—and relatively dark at night due to lack of city and roadway lights—the southwestern coastal region has a more moderate climate and several large cities. Three brightly lit urban centers are visible at image top left: Jeddah, Mecca, and Taif. Jeddah is the gateway city for Islamic pilgrims going to nearby Mecca, a religious journey known as the Hajj. Taif is located on the slopes of the Sarawat Mountains and provides a summer retreat for the Saudi government from the desert heat of the capital, Riyadh.
Bright yellow-orange lighting marks highways that parallel the trend of the Asir Mountains (image center), connecting Mecca to the resort cities of Al Bahah and Abha. Smaller roadways, lit with blue lights, extend to the west to small cities along the Red Sea coastline. The bright yellow-orange glow of the city of Abha is matched by that of Khamis Mushait (or Khamis Mushayt) to the northeast. The brightly lit ribbon of highway continues towards other large cities to the south (Jazan, not shown) and southeast (Najran, not shown).
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This photograph taken by an astronaut on the International Space Station (ISS) illustrates the morphology of the Strait. The relatively clear, deep-water passages of the western Strait of Tiran are visible at image left, while the more sinuous, shallow-water passage on the Saudi Arabia side can be seen at image top center. Light blue to turquoise areas around Tiran Island indicate shallow water, while the island itself is arid and largely free of vegetation. Coral reefs are also found in the strait and are a popular diving destination.
The silvery sheen on the water surface within the Strait and the south of Tiran Island is sunglint—light reflecting off the water surface back towards the observer on the ISS. Disturbances to the surface, as well as presence of substances such as oils and surfactants, can change the reflective properties of the water surface and highlight both surface waves and subsurface currents. For example, a large wave set is highlighted by sunglint at image lower right.
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Sediments deposited by the Colorado River have been filling the northern rift valley (the Salton Trough) for several million years, excluding the waters of the Gulf of California, and providing a fertile environment for the development of extensive, irrigation-aided agriculture in the region (visible as green and yellow-brown fields at image center). The Salton Sea, a favorite landmark of astronauts in low-earth orbit, was formed by the rupture of an irrigation canal in 1905 and today is sustained by agricultural runoff water.
A wide array of landforms and land uses in the Salton Trough are visible from space. In addition to the agricultural fields and Salton Sea, several metropolitan areas are visible, including Yuma, Arizona; Mexicali, Mexico; and the San Diego-Tijuana conurbation on the Pacific Coast (image left). The 72-kilometer-long Algodones Dunefield also is visible at image top right.
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At the top of the image, the Canadian Shield of southern Ontario is covered by an extensive forest canopy typical of early summer. Offshore and to the west and southwest of Pukaskwa National Park, several distinct sets of parallel cloud bands are visible. Gravity waves are produced when moisture-laden air encounters imbalances in air density, such as might be expected when cool air flows over warmer air. This can cause the flowing air to oscillate up and down as it moves, causing clouds to condense as the air rises and cools and to evaporate away as the air sinks and warms. This produces parallel bands of clouds oriented perpendicular to the wind direction. The orientation of the cloud bands in this image, parallel to the coastlines, suggests that air flowing off of the land surfaces to the north is interacting with moist, stable air over the lake surface, creating gravity waves.
The second phenomenon—sunglint—affects the water surface around and to the northeast of Isle Royale. Sunglint is caused by light reflection off a water surface; some of the reflected light travels directly back towards the observer, resulting in a bright mirror-like appearance over large expanses of water. Water currents and changes in surface tension—typically caused by presence of oils or surfactants—alter the reflective properties of the water and can be highlighted by sunglint. For example, surface water currents are visible to the east of Isle Royale that are oriented similarly to the gravity waves, suggesting that they too are the product of winds moving off of the land surface.
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Urban areas are readily recognizable as gray-white regions contrasting with surrounding brown to tan semi-arid landscape. The Barada River runs through Damascus, and is visible entering the metropolitan area at image top center. The Ghouta oasis, fed by the Barada River, once encircled Damascus but urban expansion has converted much of the oasis from agricultural to other land uses. A large region of agriculture extends to the southeast of Damascus, visible as extensive green fields at image lower right.
Today, the city is the center of a metropolitan area with a population of over 2.6 million (based on 2004 information from the Syria Central Bureau of Statistics). Current industries include textiles, food processing, and chemicals, with traditional artisan handcrafts still produced in the old core of Damascus. Most recently, the city has experienced unrest, military conflict, and loss of life stemming from the ongoing Syrian Civil War.
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Much closer to the camera—but still more than 550 kilometers (340 miles) from the ISS—is a dust plume surging out over the Red Sea and reaching most of the way to Saudi Arabia. The point source of this plume is the delta of the southern Egyptian river Khor Baraka. Astronaut images have shown that this delta is a common source for dust plumes, mainly because it is a relatively large area of exposed, loose sand and clay that can be easily lofted into the air. The river also cuts a narrow valley through a high range of hills that channels the wind, making it blow faster.
This dramatic view of the Red Sea shows the generally parallel margins of the opposing coastlines. The rift, or depression, that now holds the Red Sea has been opening slowly for about 30 million years and is nearly 300 kilometers (200 miles) wide in the region of the dust plume. The depression only began filling with seawater within the past five million years. The satisfyingly good fit between the coastlines allows the viewer to easily visualize how Africa and Arabia were once a single landmass before the Red Sea rift formed.
