Chapter 27

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# Chapter 27 - PowerPoint PPT Presentation

Chapter 27. The Water Cycle, Relative Humidity, Dew Point, Clouds, Specific Heat, Orographic Effect. BFRB Pages 117-122. Specific Heat P. 77-78 Orographic Effect P. 108. Water. exists as a solid, liquid, and gas can change from one state to another

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### Chapter27

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

BFRB Pages 117-122. Specific Heat P. 77-78 Orographic Effect P. 108

Water
• exists as a solid, liquid, and gas
• can change from one state to another
• The change from a solid to a liquid is called melting, liquid to a solid is called freezing
• Heat of Fusion = +/- 80cal/g/°C
• Add (+) 80cal/g/°C to melt ice to water
• Take away (-) 80cal/g/°C to freeze water to ice
Evaporation
• the process of water changing from a liquid to a gas
• occurs when water absorbs energy from its surroundings
• Because of this, evaporation results in the surroundings becoming cooler (think of sweating)
• Heat of Vaporization = + 540 cal/g/°C
Condensation
• the process of water changing from a gas to a liquid
• occurs when water vapor loses energy (releases heat)
• Because of this, condensation results in the surroundings getting warmer (the air surrounding the condensing water droplets heats up)
• Heat of Vaporization = - 540 cal/g/°C

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

WARM TEMPERATURE - EVAPORATION

Water Vapor in the Air
• The amount of water vapor in the air depends on the air temperature
• The warmer the air, the more water vapor it can hold (think of those hot, humid summer days)
• The actual amount of water vapor in the air is called specific humidity
Relative Humidity
• the amount of water vapor in the air, compared to how much water vapor it could hold at that temperature
• Relative humidity is a percent measurement
• Air with 100% humidity is said to be saturated (that temp air can’t hold any more water vapor)
• Precipitation (rain/snow/sleet) or condensation (dew/frost) will occur
Finding Relative Humidity
• use an instrument called a hygrometer
• One particular type of hygrometer is called a sling psychrometer
• This instrument is made of two thermometers attached to a handle
• One thermometer has a piece of gauze which is the soaked with water - This is called the WET BULB
• The other thermometer is called the DRY BULB
• These thermometers are swung in the air for a few minutes, and then the temperatures are recorded (take the wet bulb temperature first)
• The wet bulb thermometer should have a lower temperature, since it removes heat from the thermometer as water evaporates from it. Remember, evaporation is a cooling process!!!
• The two temperatures are then used to look up the relative humidity on a chart (ESRT’s Page 12 BOTTOM)
Condensation and Dew
• VIF - remember that air’s ability to hold moisture decreases as the temperature decreases
• As the air cools, its relative humidity increases EVEN THOUGH IT’S HOLDING THE SAME AMOUNT OF WATER VAPOR, THE RELATIVE HUMIDITY INCREASES, BECAUSE ITS ABILITY TO HOLD THE WATER VAPOR DECREASES.
• When the relative humidity reaches 100% (saturated), the water condenses out of the air as liquid droplets or ice crystals
• The temperature at which this will occur is called thedew point
• **The dew point can be found using the same method for relative humidity, except use the dew point chart (ESRT’s Page 12 TOP)
VIF – MAKE SURE THAT YOU USE THE CORRECT TABLE. BECAUSE I CAN GUARANTEE YOU THAT THE # FROM THE OTHER TABLE WILL BE ONE OF THE CHOICES THAT THE “EVIL ONES” PROVIDE!!!!
Condensation and Dew
• Condensation can only occur if the water has something to condense on
• VIF - Tiny particles in the air on which water molecules condense are called condensation nuclei
• This can be dust, salts, volcanic ash, soot from forest fires, chemicals from burning fuel, etc.
• * Water vapor that condenses on the ground is called dew (think of walking across wet grass in the morning)
• If the dew freezes on the ground, it is called frost
• * Water vapor condensing in the air forms clouds
• If the cloud forms close to the ground, it is called fog

Dew

Frost

Clouds
• formed by the condensation of water vapor
• There are three main types of clouds: cumulus, stratus, and cirrus
• Cumulus clouds are thick, puffy clouds. They tend to be lower in the sky
• Stratus clouds appear as low to middle sheets or layers of clouds
• Cirrus clouds appear as high, thin or “feathery” clouds. These clouds are made of ice crystals
• There are many forms of these types of clouds
• Ex. Cumulonimbus clouds often produce strong thunderstorms and can form tornadoes!!
• Nimbus – rain/storm in Latin

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

This is called the CLOUD BASE

Cumulus clouds that are white and puffy like cotton balls are "fair weather" clouds and are unlikely to produce precipitation
• They form in warm air on sunny days
• Cumulus clouds can form at almost any altitude, with bases sometimes as high as 14,000 feet
Cumulus clouds are clouds of vertical development and may grow upwards dramatically under certain circumstances
• The updrafts may be caused by intense heating of the air by the ground surface, the action of a cold front, or by extreme temperature differences between land and water
• The vertical air currents results in towering clouds with an anvil head on top called cumulonimbus clouds
Stratus clouds are low clouds, ranging in height from near the earth\'s surface up to 6,500 feet
• Stratus clouds form flat layers or uniform sheets
• Only a fine drizzle can form from stratus clouds because there is no vertical development
• Nimbostratus (nimbo = rain) clouds produce long periods of steady rain

Cirrus clouds are wispy in appearance, and resemble horsetails (they are sometimes called mares\' tails)

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

Cirrus clouds are formed almost entirely of tiny ice crystals

These are called cirrocumulus clouds because they are very high (cirrus), but have the cumulus (puffy) appearance, not the wispy appearance of regular cirrus clouds…

These are called cirrocumulus clouds because they are very high (cirrus), but have the cumulus (puffy) appearance, not the wispy appearance of regular cirrus clouds…

Precipitation
• any form of water that falls from the clouds when they become too massive be supported by the air
• Forms of precipitation include:
• Rain
• Snow
• Sleet – rain that falls through air that is below freezing
• Freezing rain – rain that freezes on contact with a surface that is below freezing (the ground)
• Hail – formed in cumulonimbus clouds (thunderstorms). These are ice balls which can be as large as a softball!! HAIL ONLY HAPPENS IN THE SUMMERTIME!!!!
• **When water condenses on nitrate and sulfate particles (from burning fossil fuels), acid rain is formed

Snow Level

Ice Level

Supercooled Rain Level

BRRRR…I’m CHILLY!

Rain Level

• Wind hits the windwardside of the mountain, rises, cools off, and condensation happens
• This forms clouds and precipitation
• As the air goes over the top, is sinks on the leeward side
• As the air sinks, it compresses together and gets warmed by friction
• Since the warmer air can hold more moisture, and since it lost moisture on the windward side, condensation does not occur (and no precipitation)!
• Occurs along the Sierra Nevada Mts. The California side is wet, the Nevada side is dry. Also, the Cascade Mountains – Seattle is wet, the rest of Washington is dry.