ChapterChapter 2727

The Water Cycle, Relative Humidity, Dew The Water Cycle, Relative Humidity, Dew Point, Clouds, Specific Heat, Orographic Point, Clouds, Specific Heat, Orographic

EffectEffect

BFRB Pages 117-122. BFRB Pages 117-122. Specific Heat P. 77-78 Specific Heat P. 77-78

Orographic Effect P. 108 Orographic Effect P. 108

WaterWater

• exists as a solid, liquid, and gasexists as a solid, liquid, and gas• can change from one state to anothercan change from one state to another• The change from a solid to a liquid is called The change from a solid to a liquid is called

meltingmelting, liquid to a solid is called , liquid to a solid is called freezingfreezing

• Heat of Fusion = +/- 80Heat of Fusion = +/- 80 cal/g/°Ccal/g/°C• Add (+) 80Add (+) 80 cal/g/°C to melt ice to watercal/g/°C to melt ice to water• Take away (-) 80Take away (-) 80 cal/g/°C to freeze cal/g/°C to freeze

water to icewater to ice

GASGAS LIQUID LIQUID SOLID SOLID

EvaporationEvaporation

• the process of water changing from the process of water changing from a liquid to a gasa liquid to a gas

• occurs when occurs when water absorbs energy water absorbs energy from its surroundingsfrom its surroundings

• Because of this, Because of this, evaporation results evaporation results in the surroundings becoming coolerin the surroundings becoming cooler (think of sweating)(think of sweating)

• Heat of Vaporization = + 540 Heat of Vaporization = + 540 cal/g/°Ccal/g/°C

EVAPORATION IS A EVAPORATION IS A

COOLINGCOOLING PROCESSPROCESS

CondensationCondensation

• the process of water changing from a the process of water changing from a gas to a liquidgas to a liquid

• occurs when occurs when water vapor loses energy water vapor loses energy (releases heat)(releases heat)

• Because of this, Because of this, condensation results in condensation results in the surroundings getting warmer (the the surroundings getting warmer (the air surrounding the condensing water air surrounding the condensing water droplets heats up)droplets heats up)

• Heat of Vaporization = - 540 Heat of Vaporization = - 540 cal/g/°Ccal/g/°C

• WARM TEMPERATURE - WARM TEMPERATURE - EVAPORATIONEVAPORATION

• COOL TEMPS – CONDENSATIONCOOL TEMPS – CONDENSATION(but the surrounding air actually heats up a little)(but the surrounding air actually heats up a little)

CONDENSATION IS CONDENSATION IS

A A WARMINGWARMING PROCESSPROCESS

Water Vapor in the AirWater Vapor in the Air • The amount of water vapor in the The amount of water vapor in the

air depends on the air air depends on the air temperaturetemperature• The warmer the air, the more water The warmer the air, the more water

vapor it can hold (think of those vapor it can hold (think of those hot, humid summer days)hot, humid summer days)

• The actual amount of water vapor The actual amount of water vapor in the air is called in the air is called specific humidityspecific humidity

Relative Humidity Relative Humidity • the amount of water vapor in the air, the amount of water vapor in the air,

comparedcompared to how much water vapor to how much water vapor it it could holdcould hold at that temperature at that temperature

• Relative humidity is a Relative humidity is a percentpercent measurementmeasurement

• Air with 100% humidity is said to be Air with 100% humidity is said to be saturated (that temp air can’t hold saturated (that temp air can’t hold any more water vapor)any more water vapor)– Precipitation (rain/snow/sleet) or Precipitation (rain/snow/sleet) or

condensation (dew/frost) will occurcondensation (dew/frost) will occur

Finding Relative HumidityFinding Relative Humidity • use an instrument called a use an instrument called a hygrometerhygrometer• One particular type of hygrometer is called a One particular type of hygrometer is called a sling sling

psychrometerpsychrometer– This instrument is made of two thermometers attached to a This instrument is made of two thermometers attached to a

handlehandle– One thermometer has a piece of gauze which is the soaked One thermometer has a piece of gauze which is the soaked

with water - This is called the with water - This is called the WET BULBWET BULB• The other thermometer is called the The other thermometer is called the DRY BULBDRY BULB

– These thermometers are swung in the air for a few minutes, These thermometers are swung in the air for a few minutes, and then the temperatures are recorded (take the wet bulb and then the temperatures are recorded (take the wet bulb temperature first)temperature first)

• The wet bulb thermometer should have a lower The wet bulb thermometer should have a lower temperature, since it temperature, since it removes heat from the removes heat from the thermometer as water evaporatesthermometer as water evaporates from it. from it. Remember, evaporation is a cooling process!!!Remember, evaporation is a cooling process!!!

• The two temperatures are then used to look up the The two temperatures are then used to look up the relative humidity on a chart (ESRT’s Page 12 relative humidity on a chart (ESRT’s Page 12 BOTTOMBOTTOM))

Condensation and DewCondensation and Dew • VIF - remember that VIF - remember that air’s ability to hold air’s ability to hold

moisture decreases as the temperature moisture decreases as the temperature decreasesdecreases

• As the air cools, its relative humidity increases As the air cools, its relative humidity increases EVEN THOUGH IT’S HOLDING THE SAME EVEN THOUGH IT’S HOLDING THE SAME AMOUNT OF WATER VAPOR, THE RELATIVE AMOUNT OF WATER VAPOR, THE RELATIVE HUMIDITY INCREASES, BECAUSE ITS ABILITY HUMIDITY INCREASES, BECAUSE ITS ABILITY TO HOLD THE WATER VAPOR DECREASES.TO HOLD THE WATER VAPOR DECREASES.

• When the relative humidity reaches 100% When the relative humidity reaches 100% (saturated), the water condenses out of the air (saturated), the water condenses out of the air as liquid droplets or ice crystalsas liquid droplets or ice crystals

• The temperature at which this will occur is The temperature at which this will occur is called thecalled the dew pointdew point

• **The dew point can be found using the same **The dew point can be found using the same method for relative humidity, except use the method for relative humidity, except use the dew point chart (ESRT’s Page 12 dew point chart (ESRT’s Page 12 TOPTOP))

VIF – MAKE SURE THAT VIF – MAKE SURE THAT YOU USE THE CORRECT YOU USE THE CORRECT TABLE. BECAUSE I CAN TABLE. BECAUSE I CAN GUARANTEE YOU THAT GUARANTEE YOU THAT

THE # FROM THE OTHER THE # FROM THE OTHER TABLE WILL BE ONE OF TABLE WILL BE ONE OF THE CHOICES THAT THE THE CHOICES THAT THE “EVIL ONES” PROVIDE!!!!“EVIL ONES” PROVIDE!!!!

• Condensation can only occur if the water has Condensation can only occur if the water has something to condense onsomething to condense on

• VIFVIF - Tiny particles in the air on which water - Tiny particles in the air on which water molecules condense are called molecules condense are called condensation nucleicondensation nuclei

• This can be dust, salts, volcanic ash, soot from This can be dust, salts, volcanic ash, soot from forest fires, chemicals from burning fuel, etc.forest fires, chemicals from burning fuel, etc.

• * Water vapor that condenses on the ground is * Water vapor that condenses on the ground is called called dewdew (think of walking across wet grass in the (think of walking across wet grass in the morning)morning)

• If the dew freezes on the ground, it is called If the dew freezes on the ground, it is called frostfrost• * Water vapor condensing in the air forms clouds* Water vapor condensing in the air forms clouds• If the cloud forms close to the ground, it is called If the cloud forms close to the ground, it is called

fogfog

Condensation and DewCondensation and Dew

DewDew

FrostFrost

Fog in San Francisco – Cloud formed on the Fog in San Francisco – Cloud formed on the ground…ground…

CloudsClouds

• formed by the formed by the condensation of water vapor condensation of water vapor • There are three main types of clouds: There are three main types of clouds:

cumulus, stratus, and cirruscumulus, stratus, and cirrus– Cumulus Cumulus clouds are thick, puffy clouds. They clouds are thick, puffy clouds. They

tend to be lower in the skytend to be lower in the sky– StratusStratus clouds appear as low to middle sheets or clouds appear as low to middle sheets or

layers of cloudslayers of clouds– CirrusCirrus clouds appear as high, thin or “feathery” clouds appear as high, thin or “feathery”

clouds. These clouds are made of ice crystalsclouds. These clouds are made of ice crystals• There are many forms of these types of There are many forms of these types of

cloudsclouds– Ex. Cumulonimbus clouds often produce strong Ex. Cumulonimbus clouds often produce strong

thunderstorms and can form tornadoes!!thunderstorms and can form tornadoes!!– NimbusNimbus – rain/storm in Latin – rain/storm in Latin

CLOUDS have CLOUDS have FLAT FLAT BOTTOMSBOTTOMS which which show where the show where the dew point dew point temperature has temperature has been reached been reached and the cloud and the cloud starts to form!starts to form!

This is called the This is called the CLOUD BASECLOUD BASE

•CumulusCumulus clouds that are white clouds that are white and puffy like cotton balls are and puffy like cotton balls are "fair weather" clouds and are "fair weather" clouds and are unlikely to produce precipitationunlikely to produce precipitation

•They form in warm air on sunny They form in warm air on sunny daysdays

•Cumulus clouds can form at Cumulus clouds can form at almost any altitude, with bases almost any altitude, with bases sometimes as high as 14,000 sometimes as high as 14,000 feet feet

• Cumulus clouds are clouds of Cumulus clouds are clouds of vertical vertical developmentdevelopment and may grow upwards and may grow upwards dramatically under certain dramatically under certain circumstancescircumstances

• The updrafts may be caused by The updrafts may be caused by intense heating of the air by the intense heating of the air by the ground surface, the action of a cold ground surface, the action of a cold front, or by extreme temperature front, or by extreme temperature differences between land and waterdifferences between land and water

• The vertical air currents results in The vertical air currents results in towering clouds with an towering clouds with an anvil headanvil head on on top called top called cumulonimbuscumulonimbus clouds clouds

•StratusStratus clouds are low clouds, clouds are low clouds, ranging in height from near the ranging in height from near the earth's surface up to 6,500 feetearth's surface up to 6,500 feet

•Stratus clouds form flat Stratus clouds form flat layerslayers or or uniform uniform sheetssheets– Only a fine Only a fine drizzledrizzle can form from can form from

stratusstratus clouds because there is no clouds because there is no vertical developmentvertical development

– NimbostratusNimbostratus (nimbo = rain) (nimbo = rain) clouds produce long periods of clouds produce long periods of steady rainsteady rain

• CirrusCirrus clouds are clouds are wispywispy in in appearance, and resemble appearance, and resemble horsetails (they are sometimes horsetails (they are sometimes called called mares' tailsmares' tails))

• They are among the They are among the highesthighest clouds, forming at elevations of clouds, forming at elevations of 25,000 feet and above, where the 25,000 feet and above, where the temperatures are far below temperatures are far below freezing freezing

• Cirrus clouds are formed almost Cirrus clouds are formed almost entirely of tiny entirely of tiny ice crystalsice crystals

These are called cirrocumulus clouds These are called cirrocumulus clouds because they are very high (cirrus), but because they are very high (cirrus), but

have the cumulus (puffy) appearance, not have the cumulus (puffy) appearance, not the wispy appearance of regular cirrus the wispy appearance of regular cirrus

clouds…clouds…

These are called cirrocumulus clouds These are called cirrocumulus clouds because they are very high (cirrus), but because they are very high (cirrus), but

have the cumulus (puffy) appearance, not have the cumulus (puffy) appearance, not the wispy appearance of regular cirrus the wispy appearance of regular cirrus

clouds…clouds…

Precipitation Precipitation • any form of water that falls from the clouds when any form of water that falls from the clouds when

they become they become too massive be supported by the airtoo massive be supported by the air• Forms of precipitation include:Forms of precipitation include:

– RainRain– SnowSnow– Sleet – rain that falls through Sleet – rain that falls through air that is below air that is below

freezingfreezing– Freezing rain – rain that Freezing rain – rain that freezes on contactfreezes on contact with a with a

surface that is below freezing (the ground)surface that is below freezing (the ground)– Hail – formed in Hail – formed in cumulonimbuscumulonimbus clouds clouds

(thunderstorms). These are ice balls which can be (thunderstorms). These are ice balls which can be as large as a softball!! as large as a softball!! HAIL ONLY HAPPENS IN THE HAIL ONLY HAPPENS IN THE SUMMERTIME!!!!SUMMERTIME!!!!

• **When water condenses on nitrate and sulfate **When water condenses on nitrate and sulfate particles (from burning fossil fuels), particles (from burning fossil fuels), acid rainacid rain is is formedformed

Rain LevelRain Level

SupercooleSupercooled Rain d Rain LevelLevel

Ice LevelIce Level

Snow LevelSnow Level

BRRRR…I’m BRRRR…I’m CHILLY!CHILLY!

• Precipitation does not occur the same everywhere Precipitation does not occur the same everywhere (OROGRAPHIC LIFT)(OROGRAPHIC LIFT)– Wind hits the Wind hits the windwardwindward side of the mountain, side of the mountain,

rises, cools off, and condensation happensrises, cools off, and condensation happens– This forms clouds and precipitationThis forms clouds and precipitation– As the air goes over the top, is sinks on the As the air goes over the top, is sinks on the

leewardleeward side side– As the air sinks, it compresses together and gets As the air sinks, it compresses together and gets

warmed by friction warmed by friction – Since the warmer air can hold more moisture, and Since the warmer air can hold more moisture, and

since it lost moisture on the windward side, since it lost moisture on the windward side, condensation condensation does notdoes not occur (and no occur (and no precipitation)! precipitation)!

• Occurs along the Sierra Nevada Mts. The California Occurs along the Sierra Nevada Mts. The California side is wet, the Nevada side is dry. Also, the Cascade side is wet, the Nevada side is dry. Also, the Cascade Mountains – Seattle is wet, the rest of Washington is Mountains – Seattle is wet, the rest of Washington is dry.dry.

Orographic Effect Animation