It may be something that every child does at one time or another. They lie on the ground, look up and watch the clouds float by. Then comes the question that most parents dread, “How did that cloud get there?” There is no easy way to explain how a cloud forms to a three year old. However if we understand the mechanics we may be able to give them an accurate answer and hope someday they really care and understand.
It all begins with an invisible thing called water vapor. Water vapor is simply water is a gaseous form. In this form water vapor is lighter than dry air. This is why is has the capability of rising above the dry air. When the water vapor rises it gets cooler and it expands. Then condensation begins.
Condensation occurs when water vapors attach to pollutants in the air. Tiny dust particles are everywhere. They come from many sources. They can come from the sea salt of the ocean, volcanoes, fires, cars and from you digging up some soil in your garden. The water attaches and becomes heavy and becomes saturated.
Most clouds are formed because the air reaches its dew point. This is the temperature where condensation occurs and the air is unable to hold anymore water. There are several factors that can cause air to rise and cool.
~ Topography
When air approaches a mountain it can not go through it so it must rise above it. This is called an orographic uplift. Cooling happens as the air rises.
~ Surface Heating
The soil is heated to about 10 centimeters by the sun. This heats the air and causes it to rise in thermals.
~ Turbulence
Just like in an airplane a sudden change of wind speed create swirls or eddies of circular moving air pockets.
~Frontal
A large mass of warm air that rises above a mass of cold and heavy air is called a front. When you watch the forecast you will see frontal boundaries pushing storms.
~ Convergence
This process is when air coming from different directions meets. As they crash together one mass is forced to rise.
Some clouds are white and others are dark and gray. What is the difference? White clouds are reflecting the sun, which is made up of all the colors of the rainbow. When all these colors are reflected together it comes out white. When a cloud gets thick enough with water and ice droplets attached to dust and pollution the sun can not reflect through. It scatters the light and then appears gray.
Perhaps the next time you find yourself on the ground gazing at the clouds passing by you will remember some of the answers to the questions you are bound to hear.
Sources:
www.weatherwizkids.com
www.sciencebuddies.org
www.intersites.co.uk
