C_M = 1

(a) TECHNICAL SPECIFICATION

Altostratus translucidus.

(b) EXPLANATION

(i) The greater part of this Altostratus, which is of a greyish or bluish colour, is translucent enough to reveal the position of the Sun or Moon. This Altostratus usually forms by the continuous evolution of a gradually thickening veil of Cirrostratus. Sometimes, especially in the tropics, it may be produced by the spreading out of the middle or upper part of a Cumulonimbus.

(ii) Altostratus does not show halo phenomena.