Clouds & precipitation: Nicole Irvine

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Clouds & Precipitation By: Nicole Irvine

Transcript of Clouds & precipitation: Nicole Irvine

Page 1: Clouds & precipitation: Nicole Irvine

Clouds & Precipitation

By: Nicole Irvine

Page 2: Clouds & precipitation: 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

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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

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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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