Altocumulus (Ac)

In these images clouds in the medium level are displayed. The clouds are so thin that an observer on the ground could see the sun shining through it. Therefore this special type of clouds is named "translucidus". Since the sun or stars might be seen through the gaps between them, the term "perlucidus" is additionally added.

Especially in the middle row the convection cell structure is arranged in the form of "Benard Cells". In a perfect world this would be a hexagonal honeycomb structure of clouds with thin lines of cloud-free air in between. The last three images show this cloud type as you could watch it from the ground.

AcTranslucPerluc1-3.jpg: S. Borrmann; flight from Frankfurt to Birmingham, 17 December 2003.

AcTranslucPerluc4-6.jpg: S. Borrmann; flight Varig RG2375 from Fortaleza to Sao Paulo, Brazil, 2 March 2004 around 4:33 p.m.

AcTranslucPerluc7-9.jpg: S. Borrmann; Kakadu National Park, Northern Territory, Australia, 2 December 2005 at 8:41 a.m. local time

Camera Parameters

An Olympus E-1 SLR camera with a 14-54 mm objective was used. Exposure and ASA sensitivity were automatically selected by the camera. The images were taken in the sRGB colour range with a resolution of 2560 x 1920 pixels x 24 colours.

In the tropics the sensor chip of the camera is often heated up to more than 30 deg C. At these high temperatures images might have a significant noise level. Then it becomes necessary to post-process them using a noise filter. This was done from AcTranslucPerluc7.jpg to Ac TranslucPerluc9.jpg. More details are described below.