Cloud Visual Opacity

Cloud Visual Opacity (Optional)

If clouds are present, GLOBE needs some information on their opacity, or how opaque the clouds are. GLOBE uses opacity rather than thickness because it means something a little different. When studying the radiative effects of clouds, GLOBE is interested in how much sunlight they let through, not in how much vertical space they take up. GLOBE uses three somewhat subjective categories to describe this:

Example of transparent cloud opacity. Transparent (more examples of transparent cloud opacity)
This describes thin clouds through which light passes easily, and through which people can even see blue sky. Note the milky bluish-whitish appearance of the cirrus clouds at left, especially those near the top of the photo.
Example of translucent cloud opacity. Translucent (more examples of translucent cloud opacity)
This describes medium-thickness clouds that let some sunlight through, but through which people cannot see blue sky. There may be some milky bluish-white near the edges and a very little bit of gray under the thickest parts, but these clouds are mostly a bright white.
Example of opaque cloud opacity. Opaque (more examples of opaque cloud opacity)
This describes thick clouds that do not allow light to pass directly, although light can diffuse through them. Such thick clouds often look gray. When the sky is overcast, or when these clouds are in front of the sun, it is impossible to tell where the sun is.

GLOBE asks for an estimate of the opacity for the cloudy part of the sky. In most cases, the opacity of clouds will vary from cloud edge to cloud center, or from one cloud to another. GLOBE asks for the predominant cloud opacity present in the sky.

When multiple cloud layers are present, submit this information for each cloud layer.

Cloud and Contrail Visual Opacity Field Guide