TYPES OF CLOUDS

Clouds are classified on the basis of appearance, form and altitude. On the basis of form, there are two major groups: (i) stratiform or layered types, and (ii) cumuliform or massive, globular !)'pes.

1. STRATIFORM CLOUDS are blanket-like, often cov­ering vast areas but are fairly thin when compared to their horizontal dimensions. They are sub-divided on the basis of elevation.
(a) High Clouds: 6000 to 12000 metres above sea-level, e.g., (i) Cirrus Cloud, a wispy, fibrous looking cloud, uften indicating fair weather; (ii) Cirrocumulus, a thin cloud often globular and rippled (this is the mackerel sky of popular
description);
(iii) Cirrostratus looks lilse a thin white sheet producing a halo around the sun or moon.
(b) Medium Clouds: 2100 to 6000 metres above sea level.
(i) Altocumulus Clouds: A layer of individual cloud masses
fitted closely together in geometric pattern; the masses appear white or somewhat grey on shaded sides, and the blue sky can be seen between individual patches of rows
of these bumpy-looking clouds with a flattened base. They indicate fine weather. (ii) Altostratus: A banked layer, often smoothly distributed over the entire sky; greyish in appear­ance, they usually have a smooth under-side and often
show the sun as a bright spot in the clouds. These are associated with development of bad weather.

(c) Low Clouds: Below 2100 metres (6900 feet) (i) Stratus: A dense, fog-like, low-lying dark-grey layer; brings 'dull weather, usually accompanied with a drizzle. (ii) Nimbos­tratus: If rain or snow is falling from a stratus cloud, it is Okta is a unit used in meteorology to measure cloud cover. One okta is equal to a cloud cover of one-eighth of the whole sky, Le., one okta represents one-eighth of cloud cover. Therefore, eight oktas are equivalent to a total cloud cover. called nimbostratus.

The prefix 'nimbo' means that precipi­tation is coming from the cloud. (Hi) Stratocumulus: A low­lying cloud layer consisting of distinct greyish masses of cloud between which blue sky is' visible; oriented at right angles to the direction of wind and cloud motion, they are generally indicative of fair or clearing weather.