Clouds

Trang Mai =**Clouds**=

Cloud is a very familiar weather phenomena to us. We observe clouds from the ground and see it in different shape and color. Looking like a bunch of cotton, cloud is actually formed of water vapor.

The invisible droplets of water vapor gather to form visible clouds.
 * Introduction**:

Although the sun first comes through the air in higher altitude, the ground has more particles to receive that energy. There are also more air near the ground to be heated up (because of gravity).According to combined gas law: (V1P1)/T2 = (V2P2)/T2, when air is heated up, its pressure and volume increase.
 * Background**:
 * 1) //Surface heating//:The sun heats up the earth's surface and heat is transferred to air. At the same time, the sun evaporates water to create water vapor wandering in the air. Water in liquid is evaporated to gas form, the water vapor move faster in the atmosphere.
 * 2) //Ari being forced to rise//: in low pressure system, wind moves from all directions to the center because high pressure pushes air away to low pressure. Since the air has no way to go, it goes upward.
 * Also, warm air can be able to hold more water vapor than cool air
 * So the air expands upward, the cooling air is no longer hold the water vapor it used to be, these water vapor is released to condense.
 * In high altitude, the water vapor condenses onto very tiny dust particles or other tiny particles floating in the air to form droplet. these droplets are the particles of cloud.
 * Process**:
 * Warm air and water vapor mix together, and they are heated up. The higher temperature it is, the greater its volume, its density increases ( d= m/V). therefore it floats in the atmosphere.
 * The air in higher altitude is still cool ( less air than the ground) while the warm water vapor in warm air is rising up. On the way upward, water vapor is cooled down, if it meets a microscopic particle floating in the air, it condense to form droplet.
 * A lot of droplets gathering together form cloud.

There are 4 kinds of cloud based on their altitude in the air. This maybe different in different geographical zone. http://www.windows2universe.org/earth/Atmosphere/clouds/formation_convergence.html http://www.windows2universe.org/earth/Atmosphere/clouds/cloud_types.html http://en.wikipedia.org/wiki/Cloud http://www.infoplease.com/ce6/weather/A0812624.html http://www.infoplease.com/ce6/weather/A0857399.html http://www.infoplease.com/ce6/weather/A0857400.html http://www.enchantedlearning.com/subjects/astronomy/planets/earth/clouds/ http://www.weatherquestions.com/How_do_clouds_form.htm http://weathersavvy.com/Q-Clouds_And_Color1.html
 * Type**:
 * High cloud (containing ice crystal because of low temperature) includes cirrus: 5000m-13000m
 * [[image:http://www.windows2universe.org/earth/Atmosphere/images/cirrocumulus1_small.jpg link="http://www.windows2universe.org/earth/Atmosphere/clouds/cloud_types.html"]]
 * Intermediate cloud includes altocumulus: 2000m-7000m
 * [[image:http://www.windows2universe.org/earth/Atmosphere/images/altocumulus1_small.jpg link="http://www.windows2universe.org/earth/Atmosphere/clouds/cloud_types.html"]]
 * Low cloud includes stratocumulus: surface-2000m
 * [[image:http://www.windows2universe.org/earth/Atmosphere/images/stratocumulus1_small.jpg link="http://www.windows2universe.org/earth/Atmosphere/clouds/cloud_types.html"]]
 * Vertical cloud includes cumulus: surface-13000m
 * [[image:http://www.windows2universe.org/earth/Atmosphere/images/cumulus3_small.jpg link="http://www.windows2universe.org/earth/Atmosphere/clouds/cloud_types.html"]]
 * Color**: first of all, we know that color is light.
 * Parts of light ( called wavelength) are scattered when the sunlight hit the cloud. This is called Mie Scattering.
 * Due to your positions and the thick of the cloud, you will see the clouds darker or whiter
 * Under the cloud-> sunlight is some kind of being blocked by the cloud-> less light->darker
 * On the side-> is illuminated by sunlight-> reflected to your eyes->whiter.
 * if the cloud is thick-> more light is blocked-> darker : that's why when it is about to rain ( the cloud is really thick because it gathers so much droplets to make a rain) -> the cloud looks really dark.
 * if the cloud is thin-> more light gets through-> whiter.
 * Cloud has more colors (for example: red / orange when sunset or sunrise, or consider rainbow) because of the color of the light being reflected by the cloud.
 * Shape**: clouds do not have any specific shapes.
 * Fact**:
 * Even in the same high temperature, one place can have clouds but another cannot, because it does not have enough water vapor to form water droplets.
 * The water droplets eventually fall down to form rain or snow ( it is 50/50 that these droplets make rain/ snow or they will turn back to water vapor). The water cycle is continuing as water returns to the Earth. This process is precipitation.
 * Clouds are seen as the shield of the Earth. When the sun light comes through the cloud, the cloud blocks some of the sunlight, and also reflects some heat and sunlight back to the Earth
 * [[image:http://www.enchantedlearning.com/ggifs/Greenhouseeffect.GIF width="272" height="211" link="http://www.enchantedlearning.com/subjects/astronomy/planets/earth/clouds/"]]
 * Clouds are important for the study of climate.
 * Clouds play important role in the environment cycle and weather.
 * Source**:
 * Source**: