Martes, Oktubre 14, 2014

Cloud Formation

Cloud

-Mass of water in sky: a visible mass of water or ice particles in the atmosphere from which rain and other forms of precipitation fall.


How Clouds are Formed: How to make a cloud in a bottle


Formation of Cloud

Air Compression and Expansion
-      When air is compressed, the motion of gas molecules increases and the air temperature rises. The opposite happens when air is allowed to escape. The air expands and cools. The expanding air pushes on the surrounding air and cools by an amount equal to the energy used up.

-Adiabatic Temperature Changes
-           Temperature changes that happen even though heat isn’t added or subtracted are called adiabatic temperature changes. They result when air is compressed or allowed to expand. When air is allowed to expand, it cools, and when it is compressed, it warms.
-Expansion and Cooling
-           As you travel from Earth’s surface upward through the atmosphere, the atmospheric pressure decreases.  As a result, the ascending air expands and cools. Unsaturated air cools at the constant rate of 10°C for every 1000 meters of ascent. In contrast, descending air encounters higher pressures, compresses, and is heated 10°C for every 1000 meters it moves downward. This rate of cooling or heating applies only to unsaturated air and is called the dry adiabatic rate.
-           If a parcel of air rises high enough, it will eventually cool to its dew point. Here the process of condensation begins. From this point on as the air rises, latent heat of condensation stored in the water vapor will be released. This slower rate of cooling caused by the addition of latent heat is called the wet adiabatic rate. Because the amount of latent heat released depends on the quantity of moisture present in the air, the wet adiabatic rate varies from 5–9°C per 1000 meters

Cloud Formation by Adiabatic Cooling
Rising air cools at the dry adiabatic rate of 10°C per 1000 meters, until the air reaches the dew point and condensation (cloud formation) begins. As air continues to rise, the latent heat released by condensation reduces the rate of cooling.



Processes That Lift Air
In general, air resists vertical movement. Air located near the surface tends to stay near the surface. Some exceptions to this happen when conditions in the atmosphere make air buoyant enough to rise without the aid of outside forces. In other situations, clouds form because there is some mechanical process that forces air to rise.

Four mechanisms that can cause air to rise are
- Orographic lifting
- When elevated terrains, such as mountains, act as barriers to air flow, orographic lifting of air occurs. The air cools adiabatically; clouds and precipitation may result.
-Frontal wedging
- Here the cooler, denser air acts as a barrier over which the warmer, less dense air rises. This process, called frontal wedging. A front is the boundary between two adjoining air masses having contrasting characteristics.
 Orographic Lifting and Frontal Wedging

-Convergence
- whenever air in the lower atmosphere flows together, lifting results. When air flows in from more than one direction, it must go somewhere. Because it cannot go down, it goes up. Convergence is when air flows together and rises ;and
-Localized convective lifting
On warm summer days, unequal heating of Earth’s surface may cause pockets of air to be warmed more than the surrounding air. occurs where unequal surface heating causes pockets of air to rise because of their buoyancy.

Convergence and Localized Convective Lifting


10 Rare Cloud Formations - Top10Stuff





References:
Microsoft® Encarta® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.
http://mhs.wcpss.net/teachers/murphy/earthscience/textbook/este182.pdf
https://www.youtube.com/watch?v=9shBFnhg72k
https://www.youtube.com/watch?v=wiFyg0i9K3M

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