https://doi.org/10.1351/goldbook.A00257
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 \(2000-6000\ \text{m}\); vertical velocities of \(0.05-0.1\ \text{m s}^{-1}\).