Clouds and precipitation
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Clouds and Precipitation Earth Science Ms. Kurtzweil
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Transcript of Clouds and precipitation
Clouds and Precipitation
Earth ScienceMs. Kurtzweil
Unit Objectives 1. Describe what happens when the
temperature of air drops to or below the dew point.
2. Identify the conditions that must exist for a cloud to form.
3. Name the main types of the clouds and the weather they predict.
4. Describe the various types of liquid and solid precipitation.
Basics
Evaporation is the changing of water from a liquid to a gas Liquid water on Earth entering the
atmosphere as water vapor (when energy is added at the sunlight)
Condensation is the changing of water from gas to a liquid Water vapor in the atmosphere
condensing into liquid water droplets in a cloud (when energy is released = cooled)
Water Cycle
* When water reaches the dew point, or saturation point, it will begin to condense
into water droplets that form a cloud.
Four ways that air may cool enough below the dew point to begin condensation:
1. Contacting a colder surface (blade of grass, cold glass)
2. Radiating heat
3. Mixing with colder air
4. Expanding when it rises
“Expanding when it rises” is KEY to cloud formation!
Frost
If the temperature is below the freezing, the dew point is called the frost point.
If the surface temperature falls below the frost point water vapor is deposited directly as ice crystals
Before a true cloud can form, water vapor still needs something to condense upon!
Condensation nuclei: tiny particles on which water vapor condenses.
-The foundations of water droplets in a cloud
Examples of possible condensation nuclei in our atmosphere:
1. Salt
2. Dust
3. Ice
4. Smoke
5. Sulfate/nitrate particlesCloud Seeding during droughts
How Do Clouds Form?
1. Water leaves the Earth’s surface.
2. Warm, moist air is less dense; it rises high up into the atmosphere.
3. At high altitudes, lower air pressure allows the air mass to expand and cool… eventually to the dew point.
4. Water condenses on condensation nuclei in the atmosphere, and…
Voila!!!
A cloud is born!
“Fog is just a cloud near to the ground.” Is this true?
There are different types of fogs, radiation or advection, but overall, fog is formed nearer to the ground than a cloud. This occurs when moist air close to the ground cools to its dew point.
Fog can be considered a cloud at ground level. Like clouds, fog is made up of condensed water droplets which are the result of the air being cooled to the dewpoint, where it can no longer hold all of the water vapor it contains. For instance, rain can cool and moisten the air near the surface until fog forms.
Radiation Fog Forms under similar conditions as dew On calm, clear nights, the ground will quickly
lose heat via radiation Cold air sinks and cools A whole layer of air is cooled below the dew
point and fog forms Common in humid valleys, near rivers or
lakes
Cloud Types The shapes of clouds show how air is moving
through them. Rising? Horizontally? Stable?
main cloud types, based on their location in the sky
Cirrus “curly”• Highest family of clouds in the sky
Stratus “sheetlike” or “layered”• Mid-level clouds
Cumulus “piled” or “heaped”• Lowest clouds, closest to Earth’s surface
Cloud Type DescriptionWhat kind of weather?
Picture
Cirrus High-level clouds.Thin, feathery, ice crystals
Just before snowfall or rainfall
Stratus Low sheets or layers
Little precipitation to heavy rains or snowfall
Cumulus Thick, puffy masses, “cotton balls”
Fair weather, maybe leading to abrupt storms
Nimbus Thick, grey masses
Rain, snow and thunderstorms
Nimbus and Stratus are the clouds that bring rain, heavy rain or snow.
Thunderstorms are usually associated to the cumulonimbus .
Precipitation
The falling of any form of water from the air to Earth’s surface
When will water leave a cloud and fall to the ground as precipitation? Basically, when gravity tells it to. Like
thick beads of condensation on a glass, when cloud droplets grow into drops heavy enough to fall to Earth, precipitation occurs.
4 major types of precipitation
Rain Large droplets (up
to 0.25 cm in diameter) that are far apart and fall rapidly
Snow Clumps of 6-sided
crystals that grow by collision
The most common type of solid ppt
4 major types of precipitation
Sleet Ice pellets that form
when rain falls through a layer of freezing air
What about “black ice” or “glare ice”? Sometimes in an ice storm, supercooled rain drops will freeze instantly as they come in contact with a cold surface such as roads, roofs, and power lines
4 major types of precipitation
Hail Solid ppt in the form of
lumps of ice Begins as raindrops falling
from a cumulonimbus cloud
Convection currents toss the droplet high up into the cloud where it freezes. It then falls to a lower level and water condenses on it as a liquid. The tossing and freezing process repeats itself and the hailstone keeps adding layers and growing larger.
Cloud Type DescriptionWhat kind of weather?
Picture
Cirrus High-level clouds.Thin, feathery, ice crystals
Stratus Little precipitation to heavy rains or snowfall
Thick, puffy masses, “cotton balls”
Fair weather, maybe leading to abrupt storms
Nimbus Thick, grey masses
