NASA Earth Observatory
Southern California's Catalina Eddy, the source of dense coastal fog, was spotted from space on Feb. 17 by NASA's Aqua satellite.
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As the east coast of the U.S. braces for Nor'easter Nemo, what's the weather been like for other countries around the world? Here, a young girl is pictured with her dog and a pony as it snows near Warsaw, Poland on Feb. 7, 2013.
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Afghan motor-cyclists ride in front of the war-damaged Darlaman Palace in Kabul on Feb. 7, 2013.
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A snow plow clears a road on Feb. 7, 2013, in Banska Bystrica, Slovakia.
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Snow covers the pavement in front of the Semperoper (Semper Opera House) in Dresden, eastern Germany, on Feb. 7, 2013.
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Pakistani Kashmiris walk through the snow in Muzaffarabad, the capital of Pakistani-administered Kashmir on Feb. 6, 2013.
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Commuters shelter from the snow under umbrellas whilst on their way to work in Tokyo on February 6, 2013.
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Indonesian people wade through a flooded main street in Jakarta on Feb. 6, 2013.
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Indonesian motorists maneuver through a flooded main street in Jakarta on Feb. 6, 2013.
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A Kashmiri fisherman rows his boat during a sunny day at Dal Lake, on Feb. 6, 2013 in Srinagar, India.
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Cars stand still on a road after snowfalls on Feb. 6, 2013 in Essen, western Germany.
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A rickshaw puller trying to protect himself from showers with umbrella on Feb. 5, 2013 in Noida, India.
In the hot summer months, coastal Californians enjoy cooler weather than inland residents thanks to a cooling offshore vortex called the Catalina Eddy.
NASA's Aqua satellite snapped a picture of weather pattern from space on Feb. 17 as the winds swirled counterclockwise west of San Diego. Clouds form a bull's-eye over the ocean between the Southern California coastline and the Channel Islands. The eddy's namesake is Santa Catalina Island, the largest of the Channel Islands.
The Catalina Eddy forms when upper-level atmospheric winds interact with Southern California's rugged coastline and islands, according to NASA's Earth Observatory. The topography combines with offshore winds blowing from the north and coastal winds coming from the south to spin marine stratus clouds in a counterclockwise direction. The eddies most often form between April and October, peaking in June, the Earth Observatory said.
The phenomenon drives the cloudy marine layer onshore during the summer, pushing hot air inland and cloaking the coast in fog during warmer months. Locally called "June gloom," the dense coastal fog and clouds can surprise tourists who arrive in Southern California expecting sunny beaches.
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