I resumed work on the project this morning and while looking for images to use in a movie I'm making about agate pocket formation, I came across a new NASA web site that I have not previously seen. The images are so cool that I just had to post a blog update to share a few, along with NASA's explanations. The web site is: http://earthobservatory.nasa.gov/
LAKE EFFECT CLOUDS AND SNOW
The first image shown above was taken of the North American Great Lakes region, acquired December 5, 2000. Lakes Nipigon, Superior, and Michigan show striking contrasts between clear and cloudy air as the wind blows from the northwest across the lakes.
As the cold air flows across the relatively warm lakes, it gathers heat and moisture from the surface. The warm moist air rises into the atmosphere and mixes vigorously with the cold dry air above. The layer of warm moist air deepens as it travels across the lake. Some of the evaporated water from the lake condenses into streamers of fog rising from the surface, while much of the moisture condenses to form a stratocumulus cloud in the upper half of the mixed layer.
The cloud-forming water droplets may freeze into ice crystals and, due to accumulated water deposition over time, grow into snowflakes. This process can generate snowstorms that produce significant amounts of snowfall downwind. It is not uncommon for lake effect snowstorms to produce as much as two feet of snow within a 24-hour period.
ACTIVE VOLCANO
After more than a month of eruption, lava continues to flow from Tolbachik, one of many active volcanoes on Russia’s Kamchatka Peninsula. The current eruption at Tolbachik began on November 27, 2012. Lava flowed up to 20 kilometers (12 miles) from a line of fissures on the volcano’s southern flank. Since then, some of the lava has cooled enough to allow snow to accumulate. Snow-covered lava flows appear gray in this natural-color satellite image. Fresher lava appears black. A faint orange glow at the head of the northern flow marks the location of an erupting fissure.
DUST STORMS
The above photo shows multiple dust plumes blew off the coasts of Iran and Pakistan on November 29, 2012. This image documents the movement of the plumes southward over the Arabian Sea. The plumes apparently arose from fine sediments near the coast. Some of the plumes were thick enough to hide the water surface below, especially two large plumes off the coast of Pakistan.
WINTER VS SUMMER
The above images show the difference between winter and summer of the Canadian Arctic Archipelago, Bylot Island. This is an 11,000-square-kilometer (4,200-square-mile) island within Canada’s Sirmilik National Park. In wintertime, snow and ice blanket the island in white, but in summertime, Bylot’s glaciers contrast with its earth-toned land cover. NASA’s Terra satellite observed Bylot Island on March 9, 2012 (top), and July 22, 2012 (bottom).
The mountains on Bylot are part of the Arctic Cordillera that stretches from Baffin Island to Ellesmere Island. The mountains cast longer shadows in the winter, thanks to the low angle of the Sun. That play of sunlight and mountains also illuminates (or leaves in shadow) glacier fronts in Bylot’s valleys. But the glaciers are much easier to spot in the summertime, stretching north or south from the mountainous spine.
Bylot Island has had a long acquaintance with glaciers. The Laurentide Ice Sheet once scoured the island, but it began to retreat sometime between 8,000 and 6,000 years ago. Multiple glaciers remained in the ice sheet’s wake, but they have continued changing. Photographs of the glaciers taken between the 1940s and the 2000s indicate that many are rapidly retreating.
Away from the glaciers, tundra vegetation overlies permafrost. The southern plain of the island hosts a plant habitat that is unusually rich. The plants provide food for herbivores such as lemmings, hares, and caribou, which in turn provide food for predators such as Arctic foxes and jaegers. The island’s importance to migratory birds prompted officials to declare it a sanctuary in 1965.
Seasonal changes are apparent in the waters around the island as well as on it. Arctic sea ice waxes and wanes annually. In early March 2012, sea ice filled Eclipse Sound, but in late July, only small remnants lingered.
SEDIMENT PLUME
The Guadalquivir River empties into the Golfo de Cádiz (Gulf of Cádiz) along Spain’s southwestern coast. In November 2012, the river delivered a heavy load of sediment to the gulf. NASA’s Aqua satellite captured the image on November 12, 2012
Thick sediment gave the Guadalquivir River a tan hue, and that same color dominated the water near the river delta. One would think that a sediment plume released into the ocean would simply fan out evenly in all directions, but the shape of this sediment plume is convoluted. The shape may be the result of complicated ocean currents.
UNUSUAL SEA ICE
The above image shows the east coast of Greenland in October 2012. The shifting swirls of white were sea ice, as observed by the NASA’s Aqua satellite on October 17, 2012. The image shows thin, free-drifting ice that moves very easily with winds and currents.
Each year, Arctic sea ice grows through the winter, reaching its maximum extent around March. It then melts through the summer, reaching its minimum in September. By October, Arctic waters start freezing again. However, the ice in the image above is more likely a remnant of old ice that migrated down to the coast of Greenland. Sea water is unlikely to start freezing this far south in October.
Until the late 1990s, ice would persist for years, growing thicker and more resistant to melt. Since the start of the twenty-first century, however, ice has been less likely to survive its trip through the southern part of the off-shore currents. As a result, less Arctic sea ice has been able to pile up and form multi-year ice.
With less thick ice there is less Arctic sea ice volume, something the researchers at the Polar Science Center at the University of Washington have modeled from 1979 to 2012. The model indicates that ice volume peaks in March through May of each year and reaches its lowest levels from August through October. But while the seasonal timing of the peaks and valleys has remained consistent since 1979, the total sea ice volume has declined
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