Chapter 23 Section 2 Chapter 23 Section 2 HandoutHandout

Clouds and FogClouds and Fog

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• A collection of small water droplets A collection of small water droplets or ice crystals falling slowly through or ice crystals falling slowly through the air a(n)the air a(n)– CloudCloud

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• The crystals or droplets that make up The crystals or droplets that make up clouds form when condensation or clouds form when condensation or sublimation occurs more quickly than sublimation occurs more quickly than the process of:the process of:– EvaporationEvaporation

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• A cloud that forms near or on Earth’s A cloud that forms near or on Earth’s surface is:surface is:– FogFog

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• What must be available for water What must be available for water vapor to condense and form a cloud?vapor to condense and form a cloud?– A solid surfaceA solid surface

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• The lowest layer of the atmosphere is The lowest layer of the atmosphere is thethe– tropospheretroposphere

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• What is present in the troposphere What is present in the troposphere that is essential for cloud formation?that is essential for cloud formation?– Tiny suspended particlesTiny suspended particles

Dust from Africa's Saharan Desert lingers in high Dust from Africa's Saharan Desert lingers in high altitudes as it crosses the Atlantic Ocean. This altitudes as it crosses the Atlantic Ocean. This picture was taken from an aircraft northeast of picture was taken from an aircraft northeast of Barbados in 2006. Cumulus clouds can be seen Barbados in 2006. Cumulus clouds can be seen poking through the tops of the dust layer, which is poking through the tops of the dust layer, which is seen as a milky white haze. seen as a milky white haze.

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• Suspended particles that provide a Suspended particles that provide a surface for water vapor to condense surface for water vapor to condense are calledare called– Condensation nucleiCondensation nuclei

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• What happens when water molecules What happens when water molecules collect on condensation nuclei?collect on condensation nuclei?– Water droplets formWater droplets form

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• What condition must the air be in for What condition must the air be in for clouds to form?clouds to form?– The rate of condensation must be higher The rate of condensation must be higher

than the rate of evaporation.than the rate of evaporation.

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• The net condensation that forms The net condensation that forms clouds may be caused byclouds may be caused by– The cooling of airThe cooling of air

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• What happens to molecules in rising What happens to molecules in rising air?air?– They move farther apart.They move farther apart.

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• What occurs in adiabatic cooling?What occurs in adiabatic cooling?– The temperature of an air mass The temperature of an air mass

decreases as the air rises.decreases as the air rises.

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• What does the adiabatic lapse rate What does the adiabatic lapse rate describe?describe?– The rate at which the temperature of The rate at which the temperature of

rising or sinking air changesrising or sinking air changes

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• What is the adiabatic lapse rate of What is the adiabatic lapse rate of clear air?clear air?– -1-1ooC for every 100m that air risesC for every 100m that air rises

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• What is the average adiabatic lapse What is the average adiabatic lapse rate of cloudy air?rate of cloudy air?– Between -0.5Between -0.5ooC and -0.9C and -0.9ooC per 100 m C per 100 m

that air risesthat air rises

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• Why does cloudy air have a slower Why does cloudy air have a slower rate of cooling than clear air?rate of cooling than clear air?– Because of the release of latent heat as Because of the release of latent heat as

water condenses.water condenses.

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• What two things happen to the What two things happen to the energy from the sun when it reaches energy from the sun when it reaches Earth’s surface?Earth’s surface?– Earth’s surface absorbs it and then Earth’s surface absorbs it and then

reradiates it as heatreradiates it as heat

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• Describe what happens to air near Describe what happens to air near Earth’s surface.Earth’s surface.– It absorbs heat, it rises, expands, and It absorbs heat, it rises, expands, and

then coolsthen cools

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• What is the name of the altitude What is the name of the altitude where net condensation begins to where net condensation begins to form clouds?form clouds?– Condensation levelCondensation level

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• How does the mixing of two bodies of How does the mixing of two bodies of moist air with different temperatures moist air with different temperatures cause clouds to form?cause clouds to form?– The combination causes the The combination causes the

temperature of air to change. The temperature of air to change. The combined air may be cooled to below its combined air may be cooled to below its dew point, which results in clouds.dew point, which results in clouds.

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• What are the results of air being What are the results of air being forced upward?forced upward?– The cooling of the air and cloud The cooling of the air and cloud

formation.formation.

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• What kind of terrain may force air What kind of terrain may force air upward?upward?– Sloping terrain, such as a mountain Sloping terrain, such as a mountain

rangerange

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• How do large clouds associated with How do large clouds associated with storm systems form?storm systems form?– As a mass of cold, dense air enters an As a mass of cold, dense air enters an

area and pushes a less dense mass of area and pushes a less dense mass of warmer air upward.warmer air upward.

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• What is the name of the process in What is the name of the process in which the temperature of an air mass which the temperature of an air mass decreases as it moves over a cold decreases as it moves over a cold surface, such as cold ocean or land?surface, such as cold ocean or land?– Advective coolingAdvective cooling

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• What happens when an air mass What happens when an air mass moves over a surface colder than the moves over a surface colder than the air is?air is?– The cold surface absorbs heat from the The cold surface absorbs heat from the

air and the air cools.air and the air cools.

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• What must happen in order for air What must happen in order for air cooled by adiabatic cooling, mixing, cooled by adiabatic cooling, mixing, lifting, or advective cooling to form lifting, or advective cooling to form clouds?clouds?– The air must be cooled to below its dew The air must be cooled to below its dew

point.point.

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• What two features are used to What two features are used to classify clouds?classify clouds?– Shape and altitudeShape and altitude

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• Name the three basic forms of Name the three basic forms of clouds.clouds.– Stratus, cumulus, and cirrusStratus, cumulus, and cirrus

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• What are the three altitude groups of What are the three altitude groups of clouds and their heights?clouds and their heights?– Low clouds (0 to 2,000m)Low clouds (0 to 2,000m)– Middle clouds (2,000 to 6,000m)Middle clouds (2,000 to 6,000m)– High clouds (above 6,000m) High clouds (above 6,000m)

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• Stratus clouds:Stratus clouds:– Clouds with a flat base forming at very Clouds with a flat base forming at very

low altitudes.low altitudes.

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• Altostratus clouds:Altostratus clouds:– Middle-altitude clouds that usually Middle-altitude clouds that usually

produce little precipitation.produce little precipitation.

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• Cumulus clouds:Cumulus clouds:– Billowy, low-altitude cloudsBillowy, low-altitude clouds

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• Cumulonimbus clouds:Cumulonimbus clouds:– High, dark storm cloudsHigh, dark storm clouds

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• Cirrus clouds:Cirrus clouds:– Feathery clouds composed of ice Feathery clouds composed of ice

crystals.crystals.

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• Cirrostratus clouds:Cirrostratus clouds:– Clouds that form at a high, transparent Clouds that form at a high, transparent

veil.veil.

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• Clouds that form where a layer of Clouds that form where a layer of warm, moist air lies above a layer of warm, moist air lies above a layer of cool air are called:cool air are called:– stratusstratus

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• What do the prefix nimbo and the What do the prefix nimbo and the suffix nimbus mean?suffix nimbus mean?– rainrain

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• How do nimbostartus clouds differ How do nimbostartus clouds differ form other stratus clouds?form other stratus clouds?– They can cause heavy precipitationThey can cause heavy precipitation

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• What does cumulus mean?What does cumulus mean?– ““piled” or “heaped”piled” or “heaped”

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• What does the characteristic flat What does the characteristic flat base of cumulus clouds represent?base of cumulus clouds represent?– The condensation levelThe condensation level

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• On what two factors does the height On what two factors does the height of a cumulus cloud depend?of a cumulus cloud depend?– On the stability of the troposphere and On the stability of the troposphere and

on the amount of moisture in the air.on the amount of moisture in the air.

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• In what kind of weather do cumulus In what kind of weather do cumulus clouds grow highest?clouds grow highest?– Hot, humid daysHot, humid days

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• What are cumulus clouds at middle What are cumulus clouds at middle latitudes called?latitudes called?– Altocumulus cloudsAltocumulus clouds

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• Name the low clouds that are a Name the low clouds that are a combination of two kinds of clouds.combination of two kinds of clouds.– Stratocumulus cloudsStratocumulus clouds

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• What do cirrus and cirro mean?What do cirrus and cirro mean?– ““curly”curly”

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• At what altitude do cirrus clouds At what altitude do cirrus clouds form?form?– At altitudes above 6,000mAt altitudes above 6,000m

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• Why does light easily pass through Why does light easily pass through cirrus clouds?cirrus clouds?– Because they are thinBecause they are thin

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• What kind of clouds often apperar What kind of clouds often apperar before a snowfall or rainfall?before a snowfall or rainfall?– CirrocumulusCirrocumulus

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• Compare and contrast fog and Compare and contrast fog and clouds.clouds.– Fog and clouds are bothe the result of Fog and clouds are bothe the result of

the condensation of water vapor in the the condensation of water vapor in the air, but fog is much nearer Earth’s air, but fog is much nearer Earth’s surface than clouds and forms surface than clouds and forms differently.differently.

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• Radiation fog:Radiation fog:– Forms due to the loss of heat by Forms due to the loss of heat by

radiation when Earth cools at night.radiation when Earth cools at night.

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• Advection fog:Advection fog:– Forms when warm, moist air from above Forms when warm, moist air from above

water moves over a cold surface.water moves over a cold surface.

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• Upslope fogUpslope fog– Forms when air rises along land slopes.Forms when air rises along land slopes.

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• Steam fog:Steam fog:– Forms when cool air moves over an Forms when cool air moves over an

inland warm body of water.inland warm body of water.

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• Why is radiation fog thickest in Why is radiation fog thickest in valleys and other low places?valleys and other low places?– Because dense, cold air sinks to low Because dense, cold air sinks to low

elevations.elevations.

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• Why is radiation fog often thick Why is radiation fog often thick around cities?around cities?– Smoke and dust particles act as Smoke and dust particles act as

condensation nuclei.condensation nuclei.

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• Where is advection fog common?Where is advection fog common?– Along coastsAlong coasts