display | more...
A Cloud Street is an arrangement of cumulus clouds in a line, which allows soaring aircraft, such as hang gliders, paragliders, and sailplanes to easily fly for long distances.

Cumulus clouds are formed when thermals reach an altitude where the moisture in them condenses, thus cumulus clouds are good markers for lift. The layer of air between the surface and the altitude where the dew point (condensation) is reached is known as the convective layer, and is the volume of air within which soaring takes place. Thermals are born at the surface from points more or less evenly distributed (on the very large scale) and tend to be produced at regular intervals of time. If there is a steady breeze then there will be a line of thermals at various stages of life downwind of each thermal producing spot. If the breeze is not so strong that it breaks up the thermals at altitude then there will be a line of cumulus clouds marking the line of thermals. The best conditions for cloud streets are when the maximum wind speed is within the convective layer (near the top).

A pilot can climb to near cloudbase and then glide to the area under the next cloud downwind and stand a very good chance of finding lift, climbing back to cloudbase, and repeating as desired. The combination of flying directly downwind and not having to "hunt" for lift allows pilots to focus on efficiency and speed, leading to long flight distances.

As the line of thermals and clouds forms the convection along the line is enhanced by lines of sink along each side. The line of shadows the clouds cast on the ground increases the temperature differential on the surface along corresponding lines. This leads to large areas of parallel cloud streets, especially where the surface disruptions are minor; the streets usually have some curvature which illustrates the large scale flow of the airmass. The areas between cloud streets are areas of strong sink, and often only gliders with exceptional performance can fly from one street to another. "Streets" can be present where thermals are produced but that are too dry for clouds to form - "blue thermals" - but without the visual cues such streets are extrememly difficult to detect and exploit.

Log in or register to write something here or to contact authors.