Clouds & precipitation: Nicole Irvine
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Transcript of Clouds & precipitation: Nicole Irvine
Clouds & Precipitation
By: Nicole Irvine
Definition: when air compresses it gets warmer, when it expands, it cools
Air at high pressures, that compresses and heats to 10 degrees Celsius, moves downward; which is called dry adiabatic rate
Air that cools after condensation begins and is released, heat then works against the adiabatic cooling; which is called wet adiabatic rate
Adiabatic Temp. Changes & Expansion/Cooling
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Definition: elevated terrains act like barriers to air flow (Ex: Mountains)
On a mountain, the windward side would be cold and moist; leeward side is dry and warm
When air descends, it warms adiabatically
Orographic Lifting
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Definition: large masses of warm and cold air meeting, causes a front
When the two masses of air meet, colder air is denser and is like a barrier against the warmer air
Fronts that are weather producing have to do with specific storm systems; called middle-latitude cyclones
Frontal Wedging
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Definition: when air in lower atmosphere flows together it then lifts
May lead to adiabatic cooling and/or possible cloud formations
Depending on patterns of air movement, thunderstorms may form or occur
Convergance
http://zebu.uoregon.edu/ph121/converge.html
Unequal heating of Earth’s surface, on hot days, can cause pockets of air to be warmed more than the surrounding air
Localized convective lifting is a process that produces rising thermals
When parcels that are warm rise above the condensation level, clouds form
Localized Convective Lifting
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If temperatures drop because of expansion its because the volume of the air was forced to rise
Stable air: remains in it’s position; Unstable air: tends to rise
Clouds that have air that’s unstable are more likely to cause thunderstorms/tornadoes
Stability (Density Differences)
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Air must be saturated for condensation to occur
For water vapor to condense, it must have a surface
When condensation happens, air above the ground have condensation nuclei appear
When condensation takes place the growth rate of cloud droplets increase
Condensation
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Cirrus: high, white, thin, wispy fibers
Cumulus: flat base, appearance of rising towers
Stratus: sheets or layers that cover the sky
Types of Clouds
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3 types: Cirrus, Cirrostratus, Cirrocumulus
All of these are thin, white, and made of ice crystals
They aren’t considered precipitation makers
High Clouds
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Appear at 2,000-6,000 meters high
Larger and denser than other clouds
Light snow or drizzle may come from these clouds
Middle Clouds
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3 types: Stratus, Stratocumulus, Nimbostratus
May produce light precipitation
“Nimbus”- means rainy in Latin
“Stratus”- means cover w/ layer in Latin
Low Clouds
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Some clouds don’t fit into specific categories
Some have low height, and expand upward
When upward movement happens and the acceleration is powerful, clouds then have great vertical range to form
Clouds of Vertical Development
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Has the same appearance and structure of a cloud
Defined as a cloud with its base close to the ground
Fog can produce in mornings or nights when Earth’s surface cools by radiation
Fog
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When water is cooled below 0 degrees Celsius its called “super cooled”
Ice crystals grow as cloud droplets do, when they’re big enough they will fall
When the surface temperature is above 4 degrees Celsius, snowflakes will melt before reaching the ground
Cold Cloud Precipitation
physorg.com
Rainfall is related to clouds located below the freezing level
Rain drops formed in warm clouds have a process called “collision-coalescence” process
When large droplets move through clouds they collide and coalesce
Warm Cloud Precipitation
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In meteorology, rain means drops of water that fall from a cloud
At low temperatures, light snow made of individual six-sided ice crystals may form
Temperatures warmer than -5 degrees Celsius, cause crystals to join in large clumps
Rain and Snow
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Small particles of clear ice is called sleet
Sleet can form by a layer of air (with temperatures above freezing) overlie subfreezing near the ground
Hail produces in cumulous clouds by ice pellets growing by collecting super cooled water droplets
Sleet, Glaze, and Hail
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