Environment

Going With the Flow

ImaGeo iconImaGeoBy Tom YulsmanMay 6, 2013 4:44 AM
Bering-Strait-Sea-Ice-1024x1024.jpeg

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NASA's Terra satellite captured this image of the Bering Strait on May 2. South is up, so Alaska is to the left and Russia to the right. (Image: NASA) As temperatures warm, sea ice is breaking up in the Arctic — and it can be quite a spectacle, especially when viewed from orbit. As the image above suggests, from the vantage of space it's possible to see giant cracks opening up in the mantle of sea ice, and big white pancakes floating away into open water. The image, captured by NASA's Terra satellite on April 2, is of the Bering Strait between Alaska and Siberia. South is actually up, which means Alaska is to the left and Siberia is to the right. (Look for the dissected terrain amidst the snow, clouds and ice.) The more open water toward the top of the image is the Bering Sea, and toward the bottom is the more ice-clogged Chukchi Sea, which is on the margin of the Arctic Ocean. At first glance, it looks like sea ice is fracturing in the Chukchi Sea and trying to squeeze south through the 50-mile wide strait. When I compared images over the course of several days, I could indeed see big pancakes of sea ice moving that way between May 1st and the 2nd. This would be against the prevailing water currents, which flow north — pushing an average of 800,000 cubic meters of water per second from the Pacific Basin into the Arctic Basin. (That's more than four times the Amazon's flow.) So my guess is that the ice was being pushed by strong winds. But then the chunks of ice reversed direction. My sense is of ice sloshing back and forth with changes in wind direction. And then on May 5, quite a bit of ice was flushed out of the strait itself, leaving mostly open water flecked by some white patches. (You can see an Terra image of the strait on that day by clicking here.) One more thing catches my eye in this beautiful remote sensing image: the washboard pattern of clouds toward the top. The Bering Sea sometimes features "cloud streets," parallel lines of cloud that form as cold air rushing over sea ice hits the open water. But these look more like lee wave clouds, which form as an obstacle disturbs the air flow, causing standing waves in the atmosphere. Just such an obstacle is visible in the image: ice-cloaked St. Lawrence Island. Here's an image of the entire Arctic Ocean and surrounding waters from the same day:

The entire Arctic region and environs is captured in the image from NASA's Terra satellite, taken on May 2. The Bering Strait between Alaska at upper left and Siberia at upper right can be seen at the very top of the picture. (Image: NASA) Make sure to click on it to open it large, and then click on it again to get a glorious magnified view. Much of the Arctic Basin is still covered in sea ice. But the extent is shrinking as the warm season advances. According to the National Snow and Ice Data Center, the extent of Arctic sea ice in April was the seventh lowest for the month in the satellite record. This continues a trend of shrinking sea ice. This past September saw the lowest seasonal minimum ever recorded since satellite monitoring began.

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