Cirrus Clouds (Ci)

The number concentration of the ice crystals is extremely low within the Cirrus clouds. Therefore thin Cirrus clouds can be hardly noticed at high sun level, if the aircraft is within the cloud. Only if the horizontal extension of the cloud is large enough, sometimes a thin veil can be recognized. Because the cloud particles are quite large, they scatter the sun light preferentially in forward direction so that the Cirrus clouds become visible at "back-light position" of the sun. This is demonstrated in the following series of images.

In Aircraft1.jpg Cirrus clouds can be recognized at the level of the wings and above them at a cruising altitude of 11 km. In Aircraft2.jpg the sun appears through the cloud veil that is therefore clearly noticeable. Besides the sun is "washy", but not sharp and circular. This indicates scattering at ice crystals. More details can be found in the chapter Sun through clouds.

In Aircraft3.jpg and Aircraft5.jpg it becomes apparent that the Cirrus clouds were in direct neighbourhood to the McDonnell-Douglas MD-11 aircraft.

In Aircraft4.jpg even single fumes which move over the wings and thus are directly next to the aircraft can be noticed. Considering a flight velocity of 200 m/s the cloud air moves approximately one meter during the time of exposure of 1/200 s. Therefore the fumes over the wings are not clearly reproduced.

Aircraft6.jpg proves that backwards scattering on large Cirrus crystals also leads to well-visible results. Here the sun is above and behind the observer. The Cirrus cloud is again close to the aircraft. However, this Cirrus cloud is optically much thicker in comparison to the other pictures. In both cases the vicinity to the aircraft gives an impression of the extremely small vertical extension of the cloud. It might be in the range of the wingspan for both of them, most probably even smaller.

Aircraft1-5.jpg : S. Borrmann, flight from Frankfurt to Sao Paulo, 17/18 February 2004, 4:43 a.m. to 4:49 a.m. local time at Sao Paulo, Brazil

Aircraft6.jpg: S. Borrmann, flight from Sao Paulo to Fortaleza, 18 February 2004, 12:12 p.m. local time at Sao Paulo, Brazil


Camera Parameters

Olympus E-1 SLR with a 14-54 mm objective. Light exposure and ASA sensitivity are chosen by program automation of the camera. Since the illumination was very weak, the noise of the CCD recording element affected quality. However, this could be reduced by the "noise reduction" function of the camera. The images were taken in the sRGB colour range with a resolution of 2560 x 1920 Pixel x 24 colours.