pbuttigieg
commented
4 years ago Thank you for this thorough assessment @raissameyer I think this brings a good degree of systematics to the cloud hierarchy, so would welcome a pull request with these revisions.
Some issues include
- the ☁️fluffiness☁️ of terms like "especially", "considerable", "nearly always" etc can those be made more precise? I see that this is actually the language of the Cloud Atlas, which suggests that this is the limit of the precision we can expect, however, we then have to think about how we can handle this uncertainty smartly. What happens if you move all of those components to the comment? Do the definitions of genera then start to overlap?
- The aspect of shading and dark/light parts seems very observer-centric, which can lead to weaker definitions. What does the shading imply about the actual structure/thickness of the cloud? Or is it not that simple?
- "may allow a clearly visible outline of the local star to be seen through its mass" Is another observer-centric differentia that is difficult to work with. We're assuming 20/20 human vision? If there's a way to actually comment on the density/thickness it would be better. Moving that to the comment is also an option.
raissameyer
Following #996, I would like to modify the cloud genera terms in ENVO according to WMO following this structure:
I welcome your thoughts and suggestions for improvements!
Cirrus cloud
Definition ENVO, WMO def, WMO composition, WMO étage A cloud which 1) is often present in aggregates where individual cirrus clouds are organised in patches or narrow bands of detached filaments with fibrous appearance and/or a silky sheen, 2) is almost exclusively composed of ice crystals, 3) occurs in the high atmospheric level (high étage), 4) is white or mostly white.
Cirrocumulus cloud
Definition ENVO, WMO definition, WMO composition, WMO étage A cloud which 1) is organised as a thin patch, sheet or layer without shading, composed of very small, regularly arranged, merged or separated structural elements such as grains and ripples, 2) is composed almost exclusively of ice crystals, 3) occurs in the high atmospheric level (high étage), 4) is white. Comment Most of the small structural elements have an apparent width of less than one degree. Strongly supercooled water droplets may occur but are usually rapidly replaced by ice crystals.
Cirrostratus cloud
Definition ENVO, WMO definition, WMO composition, WMO étage A cloud which 1) is organised as a transparent, whitish veil of fibrous (hair-like) or smooth appearance, 2) is composed of a relatively sparse number of mainly small ice crystals, 3) occurs in the high atmospheric level (high étage), 4) often produces halo phenomena when scattering visible range stellar radiation.
Altocumulus cloud
Definition ENVO, WMO definition, WMO composition, WMO étage A cloud which is 1) is organised as a patch, sheet, or layer often with shading, composed of laminae (a layer or layers), rounded masses, or rolls, which are sometimes partly fibrous or diffuse and which may or may not be merged, 2) is invariably composed of water droplets, 3) occurs in the middle atmospheric level (middle étage), 4) is white, grey, or both white and grey. Comment Most of the regularly arranged small elements in this cloud type often have an apparent width of between one and five degrees.
Altostratus cloud
Definition ENVO, WMO definition, WMO composition, WMO étage A cloud which 1) is organised as a sheet or layer of striated (grooves or channels in cloud formations, arranged parallel to the flow of the air), fibrous or uniform appearance, 2) is composed of water droplets and ice crystals, 3) occurs in the high atmospheric level (high étage), 4) has parts thin enough to reveal the local star, at least vaguely, as through ground glass or frosted glass, 5) is greyish or bluish in colour. Comment Altostratus clouds do not produce halo phenomena when scattering visible range stellar radiation. Altostratus is usually found in the middle atmospheric level (middle étage), but it often extends higher.
Nimbostratus cloud
Definition ENVO, WMO definition, WMO composition, WMO étage A cloud which 1) is organised as a layer, 2) is composed of water droplets (sometimes supercooled) and raindrops, of snow crystals and snowflakes, or of a mixture of these liquid and solid particles, 3) occurs in the middle atmospheric level (middle étage), 4) is diffused by more or less continuously falling rain or snow, which in most cases reaches the ground, 5) is thick enough throughout to blot out the appearance of the local star, 6) is grey, often dark grey in colour. Comment Low, ragged clouds frequently occur below the layer, with which they may or may not merge. Nimbostratus is almost always found in the middle atmospheric level (middle étage), but it usually extends into the other two levels.
Stratocumulus cloud
Definition ENVO, WMO definition, WMO composition, WMO étage A cloud which 1) is structurally organised as a patch, sheet or layer that a) almost always has dark parts and b) is composed of non-fibrous tessellations, rounded masses, rolls, and similar structural elements and which may or may not be merged, 2) is composed of water droplets, sometimes accompanied by raindrops or, more rarely, snow pellets, snow crystals and snowflakes, 3) occurs in the low atmospheric level (low étage), 4) is grey or whitish, or both grey and whitish in colour. Comment Most of the regularly arranged small structural elements of stratocumulus clouds have an apparent width of more than 5 degrees. Fibrous structural elements may emerge when virga is formed.
Stratus cloud
Definition ENVO, WMO definition, WMO composition, WMO étage A cloud which is 1) is structurally organised as a layer with a fairly uniform base or, less frequently, ragged patches, 2) is usually composed of small water droplets, 3) occurs in the low atmospheric level (low étage), 4) is disposed to produce drizzle, snow or snow grains as preciptation, 5) may allow a clearly visible outline of the local star to be seen through its mass, 6) is generally grey in colour, 7) only produces halo phenomena at very low temperatures.
Cumulonimbus cloud
Definition ENVO, WMO definition, WMO composition, WMO étage A cloud which 1) has the form of a dense mountain or one or more huge towers, 2) is composed of water droplets and, especially in its upper portion, ice crystals, 3) occurs in the low atmospheric level (low étage), 4) has a considerable vertical extent, 5) is usually smooth, fibrous or striated, and nearly always flattened across part of its upper portion, which often spreads out in the shape of an anvil or vast plume, 6) has a very dark base which may be merged with low ragged clouds which frequently form underneath this cloud, 7) is frequently associated with precipitation, sometimes in the form of virga. Comment Cumulonimbus usually have their bases in the low atmospheric level (low étage), but their vertical extent is often so great that their tops may reach into the middle and high atmospheric levels (middle and high étage). Cumulonimbus also contains large raindrops and, often, snowflakes, snow pellets or hailstones. The water droplets and raindrops may be substantially supercooled.