altostratus cloud

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 2000 m - 6000 m; vertical velocities of 0.05 m s −1 - 0.1 m s −1.
PAC, 1990, 62, 2167 (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2180