Cirrus Clouds (Ci)

The same is true for Cumulus and for Cirrus clouds: in the tropics they are not generally different from those in other regions. However, since the tropopause is found at much higher altitudes in the tropics, compared to the medium and the polar latitudes, the temperatures at which cirrus clouds occur will be much lower in the tropics.

On 2/18/2004 the flight from Sao Paola to Fortaleza ran at a cruising altitude of 11.3 km with an outside temperature of - 49 deg C. On its way back the aircraft flew again at 11.3 km, but this time the ambient temperature was -54 deg C. Because in both cases temperatures were well below -35 deg C, it can be assumed, that any cloud particles consist of ice.

Even liquid, under-cooled droplets must freeze under these conditions. This is the case for all images except Tropics21.jpg where the aircraft has already started to land. It can be recognized that the Cirrus clouds were located clearly above the cruising altitude.

Tropics1.+2.jpg show uncinus-like Cirrus clouds. Hook-like virgae, which consist of sedimenting ice-particles can be also noticed in Tropics3.jpg und Tropics4.jpg below the cloud. The other images show views of thin Cirrus clouds with varying structure which are found to be relatively close above the aircraft. The clouds in the lower level are typical tropical Cumulus clouds (see Tropical Cumulus clouds).

Tropics1-12.jpg: S. Borrmann, flight from Sao Paolo to Fortaleza in Brazil, 18 February 2004 between noon-time and 2:00 p.m.

Tropics21-27.jpg: S. Borrmann, flight Varig RG2375 from Fortaleza to Sao Paulo in Brazil, 2 March 2004 between 3:30 p.m. and 3:45 p.m.

Camera Parameters

Olympus E-1 SLR with 14-54 mm objective. Exposure and ASA selectivity choice were performed by the program automation of the camera. The images were taken in the sRGB colour range with a resolution of 2560 x 1920 Pixel x 24 colours. A polarisation filter was not used, since it produces interfering colour effects caused by the airplane windows.