Cumulus Clouds (Cu)
Cu humilis
Smog BL Top Clouds
BL Top Clouds - Dust
Cu congestus I
Cu congestus II
Cu con praecipitatio
Con congestus IV
Con congestus V
Cu ´magritteus`
Cu mediocris
Cu pileus
Cu arcus
Tropical Cu
Marine BL



Cumulus arcus Clouds

Phenomenology: Long sickle-like cloud rotors which sometimes are also called "Cumulus arcus" result from gust winds. At the front end of Cumulonimbus clouds an outflow of cold air from the cloud base downwards occurs. Under certain complex fluid-mechanical circumstances a rotor cloud can be generated. This happens only when the outflow of cold air is associated with rain and is slowly drifting away from the main rainfall region and this air is much colder than the environment at the same time.

This cloud can reach a linear extension of 100 km length. Wind velocities over 160 km/h can be associated to these squall rotors such that they might pose a risk for the air traffic. These images are copied from the chapters Tropical Rain and Squall line from Cb. Details about the whole atmospheric situation and the camera parameters are described there.

CuArcus1+2.jpg: S. Borrmann, Morro Branco near Fortaleza, Ceara, Brasilia, 24 February 2004, from 6:37 a.m. to 6:42 a.m.

CuArcus3-5.jpg: S. Borrmann, Fortaleza, Ceara, Brasilia, 29 February 2004, from 7:41 a.m. to 7:45 a.m.

Camera Parameters

An Olympus E-1 SLR with a 14-54 mm objective was used. All images were recorded with a sensitivity of 100 ASA within in the colour range sRGB. The exposure time was chosen automatically by the camera. The images have a resolution of 2560 x 1920 pixels x 24 colours.

Cumulus arcus Clouds - Roll Cloud