Weather n Climate

Want to be an Ace Cloud Reporter

Staring up at the blue skies how often have you imagined funny floating shapes in the clouds. Has the dark grey menacing clouds ever affected your moods. Well, clouds come in millions of many shapes and sizes, from little powder puffs dotting the blue skies to the deepest of greys.
If you are asked to identify these clouds you probably would want to know what they are named and how they are coded by the meteorological departments world over.
But, why do we need to code clouds at all? By understanding clouds you can comprehend and anticipate the weather. Perhaps you will be the spoilt sport who will predict a rainy afternoon on a picnic day! Airmen too find the understanding of clouds very useful in navigating their aircrafts safely.

photo-1

How are different forms of clouds formed?
Stratiform clouds form where air layers begin to rise gradually over stable underlying denser layers. As the displaced sheet of air continues to rise, it is adiabatically cooled, and condensation takes place. As the rising air is in the form of a sheet it covers a large extent and the clouds formed have a huge horizontal expanse. These clouds are capable of bringing substantial amounts of rain and snow.
On the other hand cumuliform clouds are globular masses and represent pockets of rising air which are less dense than the surrounding air. These clouds do not have a large horizontal expanse and bring rain and snow to only limited areas.
However, all said and done, we must remember that specific clouds can be created only if there are sufficient conditions fulfilled in terms of moisture content in the air, surface and air temperature, upper and lower air circulation and so on.
Through the study of clouds one can predict ground conditions accurately.
You may have been wondering why the name cirro is prefixed to several cloud names. Clouds having the same general level but differing appearances have been assigned the name cirro. Although all these clouds are essentially composed of ice-crystals they do not produce any precipitation and indicate fair weather.
Sit down with your easel when you are around these clouds because they either acquire brilliant colours at sunset or dawn or produce romantic moonlit halos in the sky.

What are the clouds found in the family of high clouds?

Cirrus
These clouds are the lace makers inspiration, delicate white and wispy. They form streaks, stringers or narrow bands across blue skies. Cirrus clouds do not interfere with the passage of sun or moonlight.
These are high clouds, which often show the presence of jet-stream circulation in the upper atmosphere. If you have observed these clouds moving slowly in parallel bands, you can be sure that there are jet streams around.
Visit your local meteorological centre and look for the name of the upper atmospheric flow you have witnessed.

Photo Courtesy: Weather Wiz Kids

Photo Courtesy: Weather Wiz Kids

Cirrocumulus
These forms of clouds do not believe in independent existence. They are more often than not found in combination with either cirrus or cirrostratus clouds.
These clouds look like small white puffs of cotton candy that may sometimes acquire a grainy, flaky, or globular texture. These are arranged in ripples in a more or less regular pattern.
One such uniform arrangement has been popularly designated the title of ‘mackerel sky’.

Photo Courtesy: Super Teacher Tools

Photo Courtesy: Super Teacher Tools

Cirrostratus
These are ice-cloud sheets, a transparent milky white veil that covers the sky lightly. The sun’s rays are filtered and a remarkable halo is cast around both the sun and the moon. The edge of this huge sheet is punctuated with patches of cirrus or cirro-cumulus clouds.

Photo courtesy: Met Office, UK

Photo courtesy: Met Office, UK

What are the clouds found in the family of middle clouds?

Altostratus
As the word stratus suggests these clouds form a uniform thick strata of cloud cover. The edges feather out in the distance and may merge into cirrostratus. The underside of this layer is smooth and appears grey or bluish grey in colour. You can neither enjoy brilliant sunlight nor a serene moonlight because they are completely obscured and only appear to be lighted spots behind the cloud layer.
Corona is the optical effect that may be sometimes visible, as opposed to the halo which is formed in the cirro-stratus. The corona results due to the diffraction of the light b’ water droplets whereby a red or faint colour band is formed along the outer margin of the corona, that is away from the sun or moon, while in the halo the red or colour band is along the inner side of the halo.
These clouds may yield some rain and snow, although most of it usually dries up, and is reabsorbed by the warmer layers below before reaching the ground. The phenomenon is called the virga and produces a trail under the cloud which looks like shreds hanging from beneath the cloud.

Photo Courtesy: Met Office, UK

Photo Courtesy: Met Office, UK

Altocumulus
Small puffs of cloud which may be white or greyish on the underside, are fitted closely together. The blue sky may be visible somewhat through the gaps in these clouds, which are either arranged in patches or bands.
Lookout for the alto-cumulus and you are sure to find a completely original design based on geometric patterns. These clouds have such an interesting appearance that they are sometimes referred to as ‘sheep clouds’ or ‘wool pack clouds’. Sadly, these clouds do not produce halos.

Photo Courtesy: Weather Wiz Kids

Photo Courtesy: Weather Wiz Kids

What comprises the family of low clouds?

Stratus
As you are already familiar stratus clouds form a layer in the lower atmosphere. These clouds are dense, low-lying and dark grey, just what you need to plummet you into a dull dismal mood.
It has a uniform base and you do not mind getting caught and becoming slightly damp in a light drizzle, these clouds should not keep you inside.
You could perhaps find it difficult to differentiate between a status cloud and a high fog. This is because both are structure less and cover the entire sky. Sometimes this sheet may be broken in parts to give a ragged appearance.

Photo Courtesy: Jackson's Weather

Photo Courtesy: Jackson’s Weather

Nimbostratus
A deluge of rain and snow breaking from these clouds distinguishes it from stratus clouds. And of course being an ace reporter you should know that stratus clouds are darker and denser.
These clouds may be thousands of feet thick, menacing but without any bite, as it is never accompanied by lightning thunder or hail.
The nimbo prefix is derived from a Latin word `nimbus’ meaning rainstorm.

Photo Courtesy: NASA S'cool

Photo Courtesy: NASA S’cool

Stratocumulus
These are low lying grey wooly packs of clouds. But you might be able to catch a glimpse of the bright blue skies in the long rolls of grey clouds. These clouds are positioned at right angles to the direction of wind.
The sight of these clouds should send your heart aflutter, as it would indicate that you could still keep your date as the stato-cumulus clouds have heralded fair weather.
However do carry grandpa’s umbrella to nestle both of you in case individual masses yield some precipitation.

Photo Courtesy: Met Office, UK

Photo Courtesy: Met Office, UK

Which clouds belong to the family of clouds with vertical development?

Cumulus
These clouds look like a white dense wool pack located at low levels of the atmosphere. You are familiar with these clouds as you have drawn them from your pre-school days. It has sharp outlines with a flat base and a bumpy head. Sometimes the vertical extent of these clouds may be larger than its horizontal extent.
Pockets of air that is heated from below and cooled from above form cumulus clouds. In addition, just like our drawings these clouds are associated with blue skies and daylight.
At night these clouds dissipate, unless of course they transform into the frightful cumulonimbus clouds.

Photo Courtesy: weather.ou.edu

Photo Courtesy: weather.ou.edu

Cumulonimbus
These clouds have been an object of study for many years. Their towering heights, with an outspread top, termed as the ‘anvil head’ have aroused enormous interest. If you were flying above these clouds, it seems white as snow, but to observers on the surface the sky suddenly attains night time darkness.
These clouds form quickly due to several reasons ranging from frontal to cyclonic. Stay indoors when you are surrounded by them because they are unpredictable and mean. Moreover, cumulonimbus is composed of water droplets, supercooled droplets and ice crystals, snowflakes, snow pellets, ice pellets or hail stones.
Lightning, thunder, rainfall and gusty winds make a perfect backdrop for heightened drama.
Not all people find such storms threatening. People residing in the middle and low latitudes breathe a huge sigh of relief as the skies break open cooling the hot summer afternoon.

Photo Courtesy: Aviation StackExchange

Photo Courtesy: Aviation StackExchange

Dr. Cumulus to Mr. Cumulonimbus: The Total Transformation
Imagine how devastating it would be to watch fluffy friendly cumulus cotton clouds alter into a menacing thundering huge body of dark growling matter.
To begin with cumulus humilis, is a humble little soul, brimming with good feelings and fair weather. It is characterized by a small vertical extent and may appear flattened. These little clouds hardly produce any precipitation at all.
Then our little cloud grows bigger. Cumulus mediocris are of moderate vertical extent, with small protuberances and sproutings about their tops and are good spirited as they hardly spoil your day with precipitation. At best its sharp outlines will remind you of a well-nourished cauliflower.
Now, our cloud mutates further, and cumulus congestus emerges. They release abundant precipitation in the form of showers, and are sometimes known to resemble a narrow, very high tower.
So, the cloud is named towering cumulus, although a more proper designation would be cumulus castellanus. The tops of these towers occasionally are formed of small “puffs” which may detach themselves successively from the main body of the cloud. They are then carried away by the wind and disintegrate more or less rapidly, occasionally producing virga. Then comes the final stage where all hell breaks loose.
Cumulonimbuses with the anvil tops are heavy and dense clouds with enormous vertical extent and form huge mountains or towers. The clouds to the front are cumulus and towering cumulus. At least part of its upper portion is usually smooth, or fibrous or striated, and nearly always flattened.
This is the part often spreads out in the shape of an anvil or vast plume and may even reach to the tropopause. Under the base of this cloud, which is often very dark, there are frequently low ragged clouds. The precipitation is intense accompanied by a thunderous symphony and flashing lightning.
Sometimes, observing carefully you may notice that strong cumulonimbus clouds have appendages protruding from the base of the cloud. They often resemble mammary glands of warm-blooded animals and have been thus dubbed suitably as the “mammatus” clouds.
However, they hardly represent a breast fed child’s security. In fact, quite the opposite, they indicate that the atmosphere is quite unstable impending severe weather is approaching.

The other special clouds
The mountain or orographic clouds are produced by the flow of air interacting with mountainous terrain.
Cap cloud
forms when air containing water vapour is uplifted on the windward side of the slope and reaches saturation forming a “cap” at the summit.
Leticular clouds
are lens-shaped clouds that can result from strong wind flow over rugged terrain. Sometimes they even stack up like pancakes in multiple layers.
The strong flow produces a distinct up and down wavelike pattern on the lee side of a mountain or a large hill and the lenticular clouds tend to form at the peaks of these waves. They sometimes are very round and the edges are so well defined that they resemble flying saucers.
Lenticuler clouds are often placed into the middle cloud category since they are most common at those altitudes.
Another “specialty” cloud is one that can develop due to Kelvin-Helmholtz (K-H) instability waves and subharmonic resonance with other waves in the atmosphere.
This can result in an intertwined or spiral cloud pattern. K.-H instability is the result of strong wind shear. K-H clouds that form in early stages can resemble well-organized waves that appear to be breaking like ocean waves.
Although this cloud is assigned a category it is not a cloud at all. In fact it is formed from the vapour emitted with the exhaust of a jet engine of an airplane when they fly at high altitudes.
The cold temperatures cause the vapour to turn into ice crystals like cirrus clouds. These clouds are called “contrails” (short for “condensation trails”) and look like lines in the sky.

Honey I Shrunk the Clouds!
Have you ever wondered what is happening to our clouds as the world is slowly warming up. Weathermen, being as unpredictable as their forecasts, hold divergent views on this issue. Some climatologists revel in a rosy picture while others paint a dismal one.
The revellers say that as the atmosphere gets warmer there would be greater evaporation, forming denser and brighter clouds which would reflect sunlight back into space.
Thus more liquid water a cloud holds, greater is its thickness and opacity, and consequently greater is its capacity to reflect back the sun’s rays. As a greater amount of sun’s rays are reflected back into the atmosphere a cooling effect will be felt all over the earth. Global warming would get a break because of these clouds and, as our revellers assume, it would make the entire phenomena of global warming less severe.

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However after every day, night follows.
So, we have the doomsday prophesies to make us sit up and get scared. Anthony Del Genio of NASA’s Goddard Institute for Space Studies published an article on October 1, 2000 issue of American Meteorological Society’s Journal of Climate, which highlighted findings quite op-posed to the prevailing views.
He discovered that as the air temperature rose the clouds became thinner. Well, not that he was the first to make such an observation. There were others who had found such a link way back in 1992, over much of the world, with long-term satellite observations. But, you may ask, why on earth does that happen? “The bottoms of the clouds rise with warmer temperature, while the top of the cloud stays the same so the clouds become thinner,” explains Del Genio.
Bottoms rise, but how? Well, as the air be-comes warmer than usual, the poor about-to-be formed cloud has to rise higher and higher to get condensed and become a cloud. As Del Genio puts it, “When low clouds are present, warmer air flowing over the land tends to be drier. As the parcel of dry air rises, it has to rise farther before it saturates with enough water to form a cloud base.”
Thus the low level clouds, which as you already know, are usually thick and bring precipitation, will reflect less sunlight and intensify global warming.
Choose your pick, believe what you want! But life ahead does seem hotter and drier than usual.

Codes of Cloud Classification

Recall all that you have learnt to become an Ace Cloud Reporter. Okay now, my techno-savvy meghdoot friend, need shortcuts? Here are the International Cloud Atlas codes used by the Indian Meteorological Department. You are now equipped to send cryptic messages, intelligible only to the well informed. It is simple, for instance if it is CH0 it means table CH code figure 0, that is ‘No Cirrus Cirrocumulus or Cirrostratus’. Similarly CH9– ‘cirrocumulus cloud…. Cirriform cloud’. And so the list goes on…..

Code 3 (CH – Form of High Clouds)
Code Figures Description International Cloud Atlas Abridged Atlas Plate Numbers
(0) No Cirrus ,Cirrocumulus or Cirrostratus
(1) Cirrus in the form of filaments, strands or hooks not progressively invading the sky. (often called “Mares Tail”) 42, 43
(2) Dense Cirrus, in patches or entangled sheaves, which usually do not increase and sometimes seem to be the remains of the upper part of a Cumulonimbus; or Cirrus with sproutings in the form of small towers or battlements, or having the appearance of Cumuliform tufts. 44, 45
(3) Dense Cirrus, often in the form of an anvil; either the remains of the upper parts of Cumulonimbus, or parts of distant Cumulonimbus, the Cumuliform portions of which cannot be seen 46, 47
(4) Cirrus in the form of hocks or filaments, or both, progressively invading the sky; they generally become denser as a whole. 48, 49, 50
(5) Cirrus, often in bands converging towards one points or two points of the horizon, and Cirrostratus, or Cirrostratus alone; In either case, they are progressively invading the sky, and generally growing denser as a whole, but the continuous veil does not reach 45 degrees above the horizon. 51
(6) Cirrus, often in bands converging towards one point or two points of the horizon and Cirrostratus alone;. In either case, they are progressively invading the sky, and generally growing denser as a whole; but the continuous veil extends more than 45 degrees above the horizon, without the sky being totally covered. 52
(7) Veil of Cirrostratus completely covering the sky 53
(8) Cirrostratus not progressively invading the sky and not completely covering the sky. 54, 55
(9) Cirrocumulus alone, or Cirrocumulus accompanied by Cirrus or Cirrostratus, or both, but Cirrocumulus is the predominant cirriform cloud. 56, 57
Code 4 (CL – Form of Low Clouds)
Code Figures Description International Cloud Atlas Abridged Atlas Plate Numbers
(0) No Stratocumulus, Stratus, Cumulus or Cumulonimbus
(1) Ragged Cumulus other than of bad weather, or cumulus with little vertical extent and seemingly flattened, or both. 1, 2
(2) Cumulus of moderate or strong vertical extent generally with protuberances in the form of domes or towers, either accompanied or not by other Cumulus or by Stratocumulus; All having their bases at the same level. 3, 4, 5
(3) Cumulonimbus, the summits of which, at least partially, lack sharp outlines, but are neither clearly fibrous (Cirriform) not in the form of an anvil; Cumulus; Stratocumulus or Stratus may also be present. 6, 7
(4) Stratocumulus formed by the spreading out of Cumulus; Cumulus may also be present. 8, 9
(5) Stratocumulus not resulting from the spreading Cumulus. 10, 11
(6) Stratus in a more or less continuous sheet or layer or in ragged shreds, or both, but no Stratus Fractus of bad weather. 12, 13
(7) Stratus fractus of bad weather or Cumulus fractus of bad weather (pannus), or both: usually below Altostratus or Nimbostratus. By “bad weather” is meant the conditions which generally exist before, during or after precipitation. 14
(8) Cumulus and Stratocumulus, other than those formed from the spreading out of Cumulus; the base of Cumulus is at a different level from that of Stratocumulus. 15, 16
(9) Cumulonimbus, the upper part of which is clearly fibrous (Cirriform) often in the form of an anvil; either accompanied or not by Cumulus, Stratus. 17, 18
Code 5 (CM – Form of Medium Clouds)
Code Figures Description International Cloud Atlas Abridged Atlas Plate Numbers
(0) No Altocumulus, Altostratus or Nimbostratus
(1) Altostratus, the greater part of which is semitransparent; through this part the sun or moon may be weakly visible, as through ground glass 21, 22
(2) Altostratus, the greater part of which is sufficiently dense to hide the sun (or moon), or Nimbostratus. 23, 24, 25
(3) Altocumulus, the greater part of which is semitransparent, the various elements of the cloud change only slowly and are all at a single level. 26, 27
(4) Patches has (often in the form of almonds or fish) of Altocumulus, the greater part of which is semi-transparent; the clouds are at one or more levels and elements are continually changing in appearance. 28, 29
(5) Semitransparent Altocumulus in bands or Altocumulus in one more or less continuous layer progressively invading the sky; these Altocumulus clouds generally are growing denser as a whole; the layer may be opaque or may consist of two or more sheets 30, 31
(6) Altocumulus resulting from the spreading out of Cumulus (or Cumulonimbus) 32, 33
(7) Any one of the following cases: –
A. Altocumulus in two or more layers, usually opaque in places and not progressively invading the sky;
B. Opaque layer of Altocumulus, nor progressively invading the sky;
C. Altocumulus together with Altostratus or Nimbostratus.
34

35
36, 37

(8) Altocumulus with sprouts in the form of small towers or battlements, or Altocumulus having the appearance of Cumuliform tufts. 38, 39
(9) Altocumulus of a chaotic sky, generally at several levels. 40, 41

Source: India Meteorological Department Weather Code (1982)
Office of the Deputy Director General of Meteorology (Weather Forecasting), Pune

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