All through our atmosphere water vapor is present as an invisible gas. Through evaporation from the oceans about 90% of this water vapor joins the earth’s atmosphere. As the ocean waters get heat from the sun, a part of the water transforms from a liquid to a gas and in the warm water that gas rises.
While the sun heats the water, more rapid movement of the water molecules starts. A number of these rapidly moving molecules succeed in detaching themselves of the water below and as water vapor they run away.
But the capacity of air to hold water vapor is not unlimited. On the air temperature depend how much it can hold. For warmer air the capacity to hold water vapor is more. As the limit it reaches no more water vapor it can hold, that is, it is saturated, or the saturation point it has reached. Beyond this stage, the water vapor will start coming back to liquid form through condensation.
When the water vapor starts condensing that very temperature point is known as the dewpoint here. For the condensation process dirty air formation above ground level is the need really. Particles like dust, salt, and suspended pollutants fill in the atmosphere we live in. As condensation nuclei these materials work since for the water vapor molecules to clump around they find a role.
Condensation just above the ground is behind fog formation. Clouds are produced by condensation at higher levels. Since the process for each is absolutely identical with the other, it is quite logical to feel that fog is nothing but a cloud on the ground level.
Formation of cloud
When condensation takes place above ground level clouds are formed. Water vapor condenses into water droplets when the surrounding air temperature is above freezing point. However water may sublimate or change directly into ice crystals when air temperature below freezing point prevails. Sometimes in a supercooled state below freezing the water vapor can remain.
Since generally with altitude temperature decreases, high level clouds have tendency to form into ice crystal clouds while low level clouds may become water droplet clouds, often a combination comes of middle level clouds. Hundreds of millions of droplets and/or ice crystals join to produce clouds. On a number of factors depends the cloud type.
For the rise of the air masses three processes work. Of those convection is the first. As the sun heats the surfaces the air above the surfaces starts rising since that air too gets heated. Soil, sand and pavement are some of the surfaces that heat up faster because of their efficiency in the matter. Everywhere these warm bodies of air begin to rise, they ultimately reach the dewpoint and cloud formation is the result.
The rise of air is also possible when collision of fronts occur. Cloud formation takes place if in the warm air enough moisture is present.
Lifting of air is also possible when it faces mountain ranges and other geographic features. Further, clouds will form if enough moisture is present in the lifted air. Rare cloud shapes are often resulted from orographic lifting.
The rise of an air mass continues so long as in respect of the surrounding air it is warmer. The conditions do not get stability still the rise continues. However, with equilibrium stable conditions are quickly reached. Normally, the conditions are unstable if over warm air is present cold air in the upper atmosphere. When warm air is over cold air, stable conditions result generally.
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