Posts Tagged ‘cumulus cloud’
January 1st, 2009 | 
Author: Cumulus Clouds are found worldwide but tend to be more common in humid regions. Cumulus clouds form through convection and while the cloud base is commonly below 2,000m they can reach up to 12 miles high, and 6 miles across. Cumulus clouds are formed within columns of rising thermal air, with their base marking the level at which condensation is occurring, and this explains why all cumulus clouds in one area have their base at the same height.
As the thermal air speeds vertically upwards it draws in surrounding air at its base, and this air is cooler and drier. Cloud droplets evaporate, and cloud fragments sink, in this drier air. This prevents cumulus clouds from growing wider and stops other clouds from forming close to it.
If you look out of the window on a clear summer morning and discover that there is not a cloud to be seen in the sky, and then by mid morning there is a horde of fluffy white clouds marching across the sky, blocking out the sun, then these will be cumulus clouds. Fluffy and white, looking like cotton wool they move quickly across the sky on the breeze. Cumulus tend to be short lived, they form rapidly and they disappear rapidly.
The heat of the morning sun makes the ground warmer and so by mid-morning patches of warmed ground are overlain by larger invisible patches of warm air. This parcel of air will start to rise and carry its moisture with it, and as it rises it expands (the air pressure is lower the higher up you are) and cools and its moisture condenses into tiny cloud droplets, forming a cumulus cloud.
Sometimes a power station or an industrial chimney will introduce enough moisture into the atmosphere to cause its very own cumulus. As mentioned the clear air around surrounding the cumulus clouds is an indication of descending air, and the larger the cumulus then the larger the clear air around it. Therefore a bigger than normal patch of blue sky may indicate the approach of a sharp shower. A medium sized cumulus cloud can hold as much as 1000 tons of moisture in it.
But at the end of the day, as the sun starts to lose its heating power the convection will end, and the cumulus clouds will slowly drift, fade and disappear.
In summary, the word ‘cumulus’ comes from the Latin word for a heap or a pile, and this aptly describes their appearance. They do not tend to last very long, and consequently do not reach to great heights (unlike, for instance, cumulonimbus). Cumulus clouds are a good indication of fair weather, with perhaps the odd sharp, short shower. And finally they are more prominent in the summer months, when convection is at its greatest.
Mark Boardman BSc dip.hyp is a leading author and expert on world weather. For more information about cumulus clouds, feel free to visit these sites.
Article Source: Cumulus Clouds The small fluffy ones
Cumulonimbus cloud is a ‘heaped’ rain cloud. (Latin ‘nimbus’ translates as ‘rain’). Cumulonimbus cloud can be viewed as a bigger, more impressive version of it’s little brother, the cumulus cloud.
Occurring worldwide, except the Antarctic, cumulonimbus are most commonly found in tropical regions. They are low level clouds that extend vertically upwards to great heights, sometimes 6 miles high or more, and their base can equally be 6 miles or so across. Most commonly associated with thunderstorms, cumulonimbus cloud produces some of the world’s most violent weather.
Cumulonimbus cloud is composed of liquid droplets closer to ground level, and ice crystals high up in the upper regions. The cloud is characterised by great thermal currents with the moist air inside racing upwards at 100 mph (ten times the speed of a normal cumulus). As this warm, moist, extremely unstable air rises rapidly it cools and its moisture condenses which releases latent heat allowing the air to continue to rise. As this happens air is drawn into the cumulonimbus cloud to replace the rapidly ascending air and the cloud continues to grow.
Now ice crystal and hailstones fall through the cloud from great heights and produce downcurrents of air that exit at the base as very strong winds and start to cool the air in adjacent upcurrents. Eventually this suppresses the upcurrents and the convection ceases. As the convection stops so the cumulonimbus cloud will begin to dissipate. The life span of these clouds is, therefore, very short, just a few hours at most. However once the cloud starts to dissipate it releases its moisture – and in a big storm this can be as much as 280,000 tonnes. This of course leads to the torrential rains associated with cumulonimbus cloud.
A ’supercell’ is produced when the upcurrents and downcurrents separate so that they no longer interfere with each other. These clouds may now last for several hours. And if the wind speed and direction change in the up levels then there may be sufficient rotation for tornadoes to form.
Sometimes cumulonimbus are half hidden or totally embedded within other clouds, but on other occasions, when the downdraughts are strong they can, they can be well defined in clear skies. With these conditions the classic anvil shaped cloud may be visible from many miles away.
Because these clouds have great depth cumulonimbus are very dark when viewed from beneath as light is scattered and reflected by the ice crystals and liquid droplets in the cloud. Cumulonimbus cloud can be seen at any time of day, but are more likely to be spotted in the afternoon during spring and summer when convection is at its greatest.
Mark Boardman BSc dip.hyp is a leading author and expert on the climate. For more information about Cumulonimbus Cloud. or a look at World Weather, go and see these sites.
Article Source: Cumulonimbus Cloud