The Earth Story

Curving cloud streets Most cloud streets form over the sea, and being formed of lines of cumulus cloud directed by the prevailing wind direction, they are usually straight. Many form when cold winds blow over warmer oceans, but this example snapped by the MODIS instrument aboard the TERRA satellite over the Amazonian regions of Brazil and Bolivia traces the curved lines of a high pressure weather system. As the land heats under the tropical sun moisture evaporates up thermals (columns of heated air used by condors and glider pilots alike) and condenses when it reaches the layer of cooler air above before dissipating in the coolth of the late afternoon. Loz Image credit: NASA

Wave clouds in the southern Indian Ocean

The wake created in the winds by l'Ile aux Cochons (pig island, a 775 metre volcano in the Crozet isles about halfway between South Africa and Antarctica) is beautifully captured in the cloud formations photographed by an astronaut on the space station. I've heard clouds described as the laws of physics drawing in the air and the complex scene here displays two layers of clouds demonstrating some of these forces interacting. The lower one is forming cloud streets (see http://tinyurl.com/q84zhjw) in response to the prevailing westerlies, while the higher one are orographic, formed as the moist winds pass over the island, cooling as they rise, and condensing the water vapour within into clouds. As the air masses fall back down again after the island, they encounter alternating layers of moist and dry air and form the chevron shaped clouds in the island's wake. The clouds themselves are still, and merely mark in a visible sculpture the movements of the air masses and the interaction between humidity, altitude and temperature. The chevron clouds are forming where the air mass after passing over the island meets moist air, condensing it with its relative coolth from its recent journey to higher altitudes, while the dry regions remain free of visible cloud, since they have too little moisture to condense.

Loz

Image credit: NASA http://earthobservatory.nasa.gov/IOTD/view.php?id=77729&src=fb

Cloud streets over the Barents Sea As spring begins in the northern hemisphere and the sea ice starts to melt, the greatest temperature differential between the icy Barents Sea and the coastal waters of Russia just after its winter is such that the land remains colder than the sea. As the cold dry wind blowing over the sea ice reached the warmer moist air of the sea near the coast, the encounter spun off lines or whirling air. The clouds form in long lines down the path of these vortices whose instabilities generate cylindrical columns of rising air down their length. As the air rises and cools it condenses the moisture at the altitude where two layers of air are meeting with a temperature inversion (see https://bit.ly/2uAFkal) while the empty patches mark where the air is dropping back in a wave. Most cloud streets form over the sea, and consist of lines of cumulus cloud directed by the prevailing wind direction. Loz Image credit: NASA https://go.nasa.gov/2uAVvo7

Cloud streets and ice in the Davis straight.

This image was taken by NASA's AQUA satellite in 2013. It shows cloud streets and winter sea ice in the Davis Straight, which connects the Atlantic Ocean with Baffin Bay, and separates Canada from Greenland. Cloud streets form when cold Arctic air passes over warmer ocean, causing condensation of the warmer marine air. When the winds pass over ice, no clouds result as the wind itself is very dry. It is the temperature difference with the sea that causes condensation. They align in the direction of the prevailing winds at the altitude where toe two airs meet.

Loz

Image credit: Nasa.

The Japanese Himawari-8 weather satellite captured this video off the coast of Korea, China, and Japan. Note the “cloud streets” over the water on both sides of the peninsula - linear cloud paths being blown out over the ocean by fairly consistent wind directions. They break up a bit more out to sea as the weather pattern changes, but a really cool shot.

Spectacular view of linear clouds flowing over Perpignan, a city in southern France. These types of clouds are nicknamed “Cloud Streets” since they’re so straight, they require straight line winds and a calm atmosphere to form. Look how they appear to undulate slightly up and down as the sun rises.

Curving cloud streets Most cloud streets form over the sea, and being formed of lines of cumulus cloud directed by the prevailing wind direction, they are usually straight. Many form when cold winds blow over warmer oceans, but this example snapped by the MODIS instrument aboard the TERRA satellite over the Amazonian regions of Brazil and Bolivia traces the curved lines of a high pressure weather system. As the land heats under the tropical sun moisture evaporates up thermals (columns of heated air used by condors and glider pilots alike) and condenses when it reaches the layer of cooler air above before dissipating in the coolth of the late afternoon.  Loz

Image credit: NASA