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Fires Near Western Coast and Cloud Streets, Mexico – April 28th, 2012

20.2N 103W

April 28th, 2012 Category: Clouds, Fires, Lakes

Mexico - April 19th, 2012

Lake Chapala, visible near the center of the right edge, appears bright silvery white due to sun glint in this image of northwestern Mexico. The southern tip of the Baja California peninsula extends into the upper left quadrant of the image. Upon opening the full image, plumes of smoke several wildfires can be seen by the mountains parallel to the coast, northwest of Lake Chapala and southeast of the peninsula.

Visible in the lower left quadrant are von Kármán vortex streets, parallel rows of swirled clouds that form as air currents pass over bluff bodies. In this case, the bluff body is Socorro Island, one of the four volcanic islands in the Revillagigedo Archipelago, belonging to Mexico.

Cloud Streets Behind Cape Verde Islands – January 30th, 2012

16.0N 24W

January 30th, 2012 Category: Clouds, Image of the day

Cape Verde - January 19th, 2012

The roughly symmetrical patterns of swirls and curves in the clouds in this image are cloud vortex streets, also known as von Karman vortices. They were created by low-level winds rushing over the Cape Verde Islands off the coast of northwestern Africa.

Von Karman vortices form nearly everywhere that fluid flow is disturbed by an object. In this image, the “object” that is disturbing the fluid flow is the group of Cape Verde islands. As a prevailing wind encounters the island, the disturbance in the flow propagates downstream of the island in the form of a double row of vortices which alternate their direction of rotation.

Cloud Streets Over Gulf of Mexico – November 6th, 2011

27.3N 94.3W

November 6th, 2011 Category: Clouds, Image of the day

Mexico - October 29th, 2011

This image shows clouds streets over the Gulf of Mexico, by the coasts of Lousiana, Texas and Mexico (counter-clockwise from upper right). Cloud streets are bands or lines of cumulus cloud that are oriented almost parallel to the low-level wind direction (with a slight angle of about 10 to 20 degrees to the left).

They usually form within the lower one to three kilometers of the atmosphere known as the planetary boundary layer and are caused by convection when the wind direction is relatively constant with height.

Multiple sources of thermals and a constant wind speed often give rise to a series of longitudinal roll vortices visible as cloud streets. This effect may be accentuated when a temperature inversion is capping the convection. The space between the cloud streets (the non-cloud streets) is about two or three times the depth of the convective layer.

Usually cloud streets have a well defined start point often following coast lines, but the end points tend to tail off as the air moves away from the source of convection. Cloud streets may from over seas as relatively cool air streams over relatively warm water, as is the case in this image, or they may be form over land as relatively unstable air streams over an obstacle and convection is caused by friction or shear.

Cloud Streets Over Lake Superior, Canada and USA

48.7N 87.6W

January 21st, 2011 Category: Clouds, Lakes

USA and Canada - January 21st, 2011

The dark blue line curving across this image is the northern shoreline of Lake Superior, bounded to the north and northeast by the Canadian province of Ontario, to the northwest by the U.S. state of Minnesota, and to the south by the U.S. states of Wisconsin and Michigan.

The rest of the lake appears crossed by parallel white lines that gradually curve from the north to the southeast. These lines are cloud streets: long rolls of counter-rotating air that are oriented approximately parallel to the ground in the planetary boundary layer.

Also visible in the image is Lake Nipigon, in the upper left quadrant. Its surface is frozen and thus appears solid white. The lake drains into the Nipigon River and thence into Nipigon Bay of Lake Superior.

Cloud Streets and Hazy Skies by Hainan Island, China

19.3N 109.8E

March 19th, 2010 Category: Clouds

China - March 5th, 2010

China - March 5th, 2010

Hainan Island (Hainan Dao) comprises all but three percent of the land mass of Hainan Province, China, despite the fact that the province includes some two hundred islands scattered among three archipelagos off the southern coast.

Hainan Island is located in the South China Sea, separated from Guangdong’s Leizhou Peninsula to the north by a shallow and narrow strait. To the west of Hainan is the Gulf of Tonkin. Hainan Dao has an area of 33,920 square kilometers and is China’s southernmost and smallest province. Wuzhi Mountain (1,876 m) is the highest point on the island.

Much of the land and water visible here appear hazy due to smoke from hundreds of fires blazing across Southeast Asia at the time the image was taken. Some clouds hug the southern coast of the island and reach across the sea in parallel rows, a phenomenon known as cloud streets.