CLOUDS AND PRECIPITATION

By Brendan McFadden

Adiabatic Temperature changes, expansion, and cooling.

When air is compressed, the molecules move faster and the temperature increases. When it can expand, the temperature decreases.

Every 1,000 meters from the surface the temperature goes down 10 c.

Orographic Lifting

Mountains act as barriers to prevent air flow. That is why the leeward is cooler than the windward side.

The moisture in the air decreases by the time it gets to the leeward side so it becomes dryer.

Frontal Wedging

Hot air and cool air collide causing a Front.

The cool air rises over the warm air, acting as a wall, which can prevent storm systems.

Convergence

When air comes from multiple directions it must go up.

This causes cloud formation and adiabatic temperature changes.

Localized Convective Lifting Unequal heating sometimes causes

sections of air be more heated than others.

Warmer air rises and is called a thermal. That is the process which causes convective lifting.

Stability(Density differences, stability, and daily weather).

Stable air usually stays in its original position, but unstable air rises.

The most stable conditions happen in a temperature inversion, which is when air temperature increases with height.

Clouds in unstable air can usually lead to tornados and thunderstorms.

Condensation

The air MUST be saturated before it can condense.

Condensation nuclei, which contain salt, smoke and dust particles, act as surfaces for water vapor.

Salt, Dust , and smokeWater Droplets

Types of clouds Clouds are known by their height and

form. There are 3 types of clouds. Cirrus(High

white and thin), Cumulus( Flat base and dome), and Stratus( High sheets that cover much of the sky).

http://en.wikipedia.org/wiki/Cirrus_cloudhttp://en.wikipedia.org/wiki/Cumulus_cloudhttp://urbanext.illinois.edu/kalani/18.cfm

High clouds

Cirrus, cirrostratus, and cirrocumulus make up the high clouds. They are white, thin and usually ice crystals.

This happens because low quantities of water and low temperatures.

http://www.enchantedlearning.com/subjects/astronomy/planets/earth/clouds/

Middle clouds

These clouds appear in the 2000 to 6000 meter range are middle clouds.

They are larger and denser than high clouds. They can contain light snow and rain.

http://scienceprep.org/clouds.htm

Low clouds

These clouds are a fog-like layer that sometimes has light precipitation.

Most of the clouds are gray and are in the surface to 2000 meter range.

http://photos.igougo.com/pictures-photos-p369775-Low_Clouds.html

Clouds of vertical development

Some clouds don’t fit in to any of the categories. They are formed in unstable air

The result is often thunderstorms and rain.

http://www.free-online-private-pilot-ground-school.com/Aviation-Weather-Principles.html

Fog(by cooling and evaporation)

Some fog is formed when warm moist air flows over cool currents.

Some forms when cold air leaves the water and causes it to evaporate from the water’s surface.

http://www.renderplus.com/wk/Volumetric_Fog_w.htm

Cold cloud precipitation(Bergeron Process)

Water suspended in air does not freeze until -40 c. When the water touches an ice crystal it will supercool.

This causes snow and snow crystals

Warm cloud Precipitation Rain is most of the time from clouds

above the freezing level. The collision- coalescence process causes larger drops of water to collide with smaller drops.

This will make large amounts of smaller drops and they will be slower.

https://www.meted.ucar.edu/sign_in.php?go_back_to=http%253A%252F%252Fwww.meted.ucar.edu%252Ftropical%252Ftextbook_2nd_edition%252Fnavmenu.php%253Ftab%253D6%2526page%253D3.0.0

Rain and snow

Rain is actually small drops of water that fall from clouds that of a diameter of at least .5 mm.

Snow, which usually melts before it touches the ground, clumps up with ice crystals and make a heavy moisture content.

Sleet, Glaze, and Hail

Sleet is small grains of translucent ice that fall from clouds. A layer of air near the ground must be subfreezing.

Glaze is know as freezing rain and must be super cooled below 0 c. Hail begins as small ice pellets but can supercooled and increase in size.

http://climate.met.psu.edu/features/Hail/PEMA_hail.php

The End