Altostratus (As)

Here views of wave-like altostratus clouds above the Baltic Sea are shown. These clouds are supposed to be thin altostratus clouds and not Cirrus ones, since they clearly occur below the flight level of approximately 10 km. Also above the airplane any cirrus clouds could be observed.

Such waves arise, when two adjacent layers of air move with different velocities or directions or when the air is forced to ascend while flowing over mountains. The observer only sees the border of the widespread cloud cover so that the classification "stratus" seems to be justified.

S. Borrmann, flight from Stockholm to Frankfurt, 22 June 2002, 1 p.m. to 3 p.m.