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Contrails Over Jutland Peninsula, Denmark and Germany

57.0N 8.8E

June 5th, 2013 Category: Climate Change, Clouds MODISTerra

Denmark – June 4th, 2013

Condensation trails create criss-crossed lines over the Jutland Peninsula (center), the northern part of which belongs to Denmark and the southern part of which belongs to Germany. Depending on the temperature and humidity at the altitude the contrail forms, they may be visible for only a few seconds or minutes, or may persist for hours and spread to be several miles wide. Persistent spreading contrails are thought to have a significant effect on global climate.

Contrails, by affecting the Earth’s radiation balance, act as a radiative forcing. Studies have found that contrails trap outgoing longwave radiation emitted by the Earth and atmosphere (positive radiative forcing) at a greater rate than they reflect incoming solar radiation (negative radiative forcing).

Global radiative forcing has been calculated from the reanalysis data, climatological models and radiative transfer codes. It is estimated to amount to 0.012 W/m2 for 2005, with an uncertainty range of 0.005 to 0.0026 W/m2, and with a low level of scientific understanding. Therefore, the overall net effect of contrails is positive, i.e. a warming effect.

However, the effect varies daily and annually, and overall the magnitude of the forcing is not well known: globally (for 1992 air traffic conditions), values range from 3.5 mW/m2 to 17 mW/m2. Other studies have determined that night flights are mostly responsible for the warming effect: while accounting for only 25% of daily air traffic, they contribute 60 to 80% of contrail radiative forcing. Similarly, winter flights account for only 22% of annual air traffic, but contribute half of the annual mean radiative forcing.

Vortex Streets by Canary Islands and Dust Off Mauritania

26.8N 17W

April 18th, 2013 Category: Clouds, Dust Storms

Mauritania – April 17th, 2013

The interesting paisley swirled cloud patterns southwest of the Canary Islands are Kármán vortex streets. In fluid dynamics, these are repeating patterns of swirling vortices caused by the unsteady separation of flow of a fluid around blunt bodies – in this case, the islands of the archipelago. Visible in the lower part of the image is the Bay of Arguin, in Mauritania, and a light veil of dust blowing off the coast.

Contrails Over the Bay of Biscay, Spain and France – April 17th, 2013

45.1N 3.4W

April 17th, 2013 Category: Clouds, Image of the day

Spain and France – April 17th, 2013

Contrails hang in the air over the Bay of Biscay, between Spain (below) and France (right), creating criss-crossed patterns. Contrails, or condensation trails, usually occur when clouds form around the water vapor left in the air from the exhaust of passing airplanes, although they can also be triggered by the changes in air pressure in wingtip vortices or in the air over the entire wing surface.

Haze Over Northwestern Italy

44.8N 9.1E

April 17th, 2013 Category: Clouds, Sediments

Italy – April 17th, 2013

A haze hangs over the northwestern part of Italy, over the Po Valley and along the coast to the French border, also spilling over the Mediterranean Sea towards the island of Corsica. Visible on the other side of the Italian peninsula, in the Adriatic Sea, are green sediments and algae spilling forth from the mouth of the Po River.

Popcorn Clouds Over Florida, USA

27.9N 82.4W

April 7th, 2013 Category: Clouds

USA – April 6th, 2013

Popcorn clouds speckle the skies over much of the state of Florida, USA. Visible through the clouds are bodies of water, such as Lake Okeechobee (below) and cities such as Tampa and St Petersburg (west coast) and Miami (southeast coast). This is due to the fact that popcorn clouds tend to appear only above vegetated areas, since they are formed by water vapor released by plants that rises and eventually condenses into clouds.

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