August 18th, 2010 Category: Clouds, Image of the day

USA - August 29th, 2010

The western coast of the United States of America, parallel to California’s Great Central Valley, is lined by thick white clouds. This is a common occurrence in the area due to a combination of atmospheric and oceanographic conditions.

Visible in the lower half of the image are a series of lines in those clouds, creating an almost asterisk-like shape. These long, linear cloud formations are known as ship tracks, since they form when water molecules gather around the exhaust released into the air by passing ships. The phenomenon is similar to that of condensation trails in the air from passing jets.

Tags: California Clouds Great Central Valley Ship Tracks USA |  Print This Post |  Email This Post | | Leave a comment

August 8th, 2010 Category: Clouds, Image of the day

Canary Islands - August 5th, 2010

The clouds below the Canary Islands, an archipelago off the western coast of Africa that belongs to Spain,  form lines of swirls towards the southwest. These lines are called Kármán Vortex Streets, a double row of line vortices in a fluid.

Under certain conditions a Karman vortex street is shed in the wake of bluff cylindrical bodies, such as the Canary Islands, when the relative fluid velocity is perpendicular to the generators of the cylinder. This periodic shedding of eddies occurs first from one side of the body and then from the other, an unusual phenomenon because the oncoming flow may be perfectly steady.

Tags: Canary Islands Clouds Kármán Vortex streets |  Print This Post |  Email This Post | | Leave a comment

June 19th, 2010 Category: Clouds, Image of the day

Canary Islands - June 6th, 2010

The clouds lined up in parallel rows of swirls southwest of the Canary Islands, belonging to Spain but located off the western coast of Africa, are an atmospheric phenomenon known as Kármán Vortex Streets.

They are named for the American engineer and researcher Theodore von Kármán. In 1911 he made an analysis of the alternating double row of vortices behind a bluff body (one having a broad, flattened front) in a fluid stream, now famous as Kármán’s Vortex Street.

Tags: Africa Canary Islands Clouds Kármán Vortex streets Spain |  Print This Post |  Email This Post | | Leave a comment

November 25th, 2009 Category: Clouds

Namibia - November 16th, 2009

The sands of the Namib Desert appear orange near the coast, changing to rusty red further inland. The desert stretches along 2000 km (1200 mi) of Namibia’s coastline. It is common to see clouds and fog hugging the shoreline, as can be observed here, a phenomenon caused by the interaction of moist sea air and dry desert air.

East of the desert, whose average width of the desert is only 113 km (70 mi), are the Naukluft Mountains in the Hardap Region. This massif in central Namibia forms the easternmost part of the Namib-Naukluft National Park. They are known for their wildlife, including mountain zebras and leopards. The mountains have many small streams and waterfalls, while the Never Ending Hills lie to their east.

Tags: Africa Clouds Hardap Region Namib Desert Namib-Naukluft National Park Namibia Naukluft Mountains Never Ending Hills |  Print This Post |  Email This Post | | Leave a comment

June 4th, 2009 Category: Clouds

Clouds off Chilean coast - June 2nd, 2009

The coast of central Chile borders the right side of this image, which focuses instead on cloud patterns in the Pacific Ocean.

While the areas at the top and flanking the coastline and covered by thick clouds, the central area is clearer.

Between the densely covered and the mostly clear parts, there is an intermediate transition area in which lines of small vortices are visible.

Tags: Chile Clouds Pacific Ocean |  Print This Post |  Email This Post | | Leave a comment

June 1st, 2009 Category: Clouds

West Coast, USA - May 25th, 2009

San Francisco Bay

Here, the coast of California is framed by a blanket of clouds and sea fog. Fog begins to form when water vapor (a colorless gas) condenses into tiny liquid water droplets in the air. Fog normally occurs at a relative humidity near 100%.

Another common type of formation is associated with sea fog (also known as haar or fret), due to the peculiar effect of salt. Clouds of all types require minute hygroscopic particles upon which water vapor can condense. Over the ocean surface, the most common particles are salt from salt spray produced by breaking waves.

Except in areas of storminess, the most common areas of breaking waves are located near coastlines, hence the greatest densities of airborne salt particles are there.

Condensation on salt particles has been observed to occur at humidities as low as 70%, thus fog can occur even in relatively dry air in suitable locations such as the California coast, as shown here. Typically, such lower humidity fog is preceded by a transparent mistiness along the coastline as condensation competes with evaporation, a phenomenon that is typically noticeable by beachgoers in the afternoon.

The close-up focuses on San Francisco, where the combination of cold ocean water and the high heat of the California mainland create the city’s characteristic fog that can cover its western half all day during the spring and early summer. The fog is less pronounced in eastern neighborhoods, in the late summer, and during the fall, which are the warmest months of the year.

The high hills in the geographic center of the city protect neighborhoods directly to their east from the foggy and cool conditions experienced in the Sunset District; for those who live on the eastern side of the city, San Francisco is sunnier, with an average of 260 clear days, and only 105 cloudy days per year.

Tags: Clouds Fog fret haar San Francisco San Francisco Bay USA |  Print This Post |  Email This Post | | Leave a comment

March 21st, 2009 Category: Image of the day

USA - March 19th, 2009

The white streaks in the clouds off the coast of California are not condensation trails caused by airplanes, but rather “ship tracks” from passing ships.

Ship tracks form when water molecules gather around the exhaust ships release into the air. When enough water molecules collect there, a visible cloud is formed. Ship track clouds have a long, string-like form because they stretch over the long, narrow path where the exhaust particles have been blown by the wind.

The particles billowing from ships’ smokestacks enter the air above the eastern Pacific and create long, thin clouds that remain there for days.

This is because the air above the oceans generally suffers from less turbulence and convection than the air above land. The lower atmosphere is especially calm over the eastern Pacific in the summertime due to a layer of hot air that settles in 500 to 700 meters above that region of the ocean.

This effect creates a temperature inversion, placing a cap on the cooler air below, trapping pollutants and water vapor. While the inversion is responsible for the smog that reduces air quality in Los Angeles, it also allows for the formation of long lasting ship tracks.

Tags: California Clouds Pacific Ocean Ship Tracks |  Print This Post |  Email This Post | | Leave a comment

March 17th, 2009 Category: Snapshots

Ship tracks in Pacific Ocean - March 15th, 2009

Although they seem like condensation trails from passing airplanes, these criss-crossed lines over the Pacific Ocean, south of Alaska, are actually from ships.

Such streaks are called ship tracks.  Ship tracks are clouds that form around the exhaust released by ships into the still ocean air.

Water molecules collect around the tiny particles (aerosols) from exhaust to form a cloud seed. More and more water accumulates on the seed until a visible cloud is formed.

In the case of ship tracks, the cloud seeds are stretched over a long, narrow path where the wind has blown the ship’s exhaust, so the resulting clouds resemble long strings over the ocean.

Tags: Alaska Clouds Pacific Ocean Ship Tracks |  Print This Post |  Email This Post | | Leave a comment

March 5th, 2009 Category: Rivers

Gulf of Khambat, India - March 3rd, 2009

Close-up of clouds

Close-up of rivermouth

Reddish brown sediments flowing out of the Narmada (east) and Sabarmati (north) Rivers create streaks in India’s Gulf of Khambhat (formerly known as the Gulf of Cambay), an inlet of the Arabian Sea.

The Kathiawar Peninsula forms the western coast of the gulf.  A range of low hills, known as the Gir Hills, occupies the south-central portion of the peninsula. The highest of these is Girnar.

The other side of the peninsula forms the eastern coast of the Gulf of Kutch. This gulf also contains an algal bloom, though there are fewer sediments. These are lighter and more golden brown in color, due to differences in soil content.

The salty marshes of the Rann of Kutch are visible north of the gulf of the same name, and the Indus River in Pakistan can be seen on the far left.

One close-up focuses on the rivermouths and gulfs, while the other focuses on an interesting cloud pattern visible to the south of the continent in the full image.

Tags: Arabian Sea Clouds Gir Hills Girnar Gujarat Gulf of Cambay Gulf of Khambhat Gulf of Kutch India Indus River Kathiawar Peninsula Narmada River Pakistan Rann of Kutch Sabarmati River Sediments |  Print This Post |  Email This Post | | Leave a comment