in atmospheric chemistry
A grey, uniform, striated or fibrous sheet but without halo phenomena, and through which the sun is seen only as a diffuse, bright patch or not at all; usually at elevations \(\text{2000–6000 m}\); vertical velocities of \(\text{0.05–0.1 m s}^{-1}\).
PAC, 1990, 62, 2167. (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2180 [Terms] [Paper]