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Essential Question:
Water in the Atmosphere (Chapter 18)
Characteristics of Water
 solid state at 0o or below; appears as ice, snow, hail, and ice crystals.
 liquid state between 0o and 100o; appears as rain and cloud droplets.
 gas state 100o or higher. This is an invisible gas referred to as water vapor.
 Energy is either absorbed or released when water changes state.
o changing from a gas to a liquid is called condensation, energy is
released.
 Products of condensation are dew, fog and clouds.
 condesation slows down the rate at which air cools.
o changing from liquid to a gas is called evaporation, energy is absorbed
 evaporation is a cooling process, the water molecules absorbed
the heat as they evaporate.
Humidity
 Humidity is the amount of water vapor present in the air.
 Specific Humidity: actual amount of water vapor in the air at a given time or
place.
 Relative Humidity is what meteorologist report in weather forecasts.
o Relative Humidity is how near the air is to maximum capacity for
holding water vapor.
o Relative humidity is usually stated as a percentage (%).
 Saturated: when air cannot hold anymore water vapor.
o Amount evaporating equals the amount of condensation forming
o The amount of water vapor in saturated air is dependent on the
temperature.
o The warmer the air the more water vapor it can hold.
 Humidity is measured using a psychromter and a relative humidity chart.
o The psychrometer, works on the principle that evaporation causes
cooling.
o The psychrometer consist of two thermometers, one wet bulb and one dry
bulb.
Summary:
Essential Question:
Condensation
 Condensation: is the changing of water vapor to a liquid.
o night air cools more rapidly and when it cools past the point of
saturation, condensation occurs.
o Water vapor condensing in the atmosphere, forms clouds or fog.
o Water vapor condensing on surfaces is called dew.
 Dew Point is the temperature at which saturation occurs and condensation
begins.
o The more water vapor in the air the less the air has to cool in order for
condensation to begin.
Cooling and Condensation
 Two conditions are required for condensation to occur.
1. Condensation nuclei must be present
2. Air must cool to or below the dew point.
 Condensation nuclei are usually substances such as salt, sulfate, particles, nitrate
particles, ash, dust.
 Air may cool or lose heat through the following ways:
o Contact with a colder surface
o Radiation or heat
o Mixing with colder air
o Expansion as it rises
 Dew/Frost form when moist air contacts a colder surface.
o Air temp above 0oC dew forms
o Air temp below 0oC frost forms
 Fog forms when air cools through contact and mixing with colder air
Summary:
Essential Question:
Clouds
 There are four types of clouds
o Low clouds
o Middle clouds
o High clouds
o Vertical developed clouds
 classified based on their altitude and shape.
 Cloud names are formed from one or more of five words or word parts.
o Stratus or Strato: clouds that form layers
o Cumulus or Cumulo: clouds that grow upward, puffy.
o Cirrus or Cirro: feathery clouds, these clouds are high in altitude and
contain ice crystals.
o Alto: clouds located between 2000 and 7000 meters altitude.
o Nimbus or Nimbo: dark rain clouds
o
Summary:
Essential Question:
Cloud Formation
 Shape of a cloud shows how the air moves through the cloud.
o Verical developed clouds form when rising air is lighter than the
surrounding air.
 Condensation Level: the atmospheric level at which condensation occurs. (dew
point in the atmosphere)
 Rising air that cools to its dew
point
 Without a steady influx of
warm, moist air the cloud will
soon evaporate.
 clouds stop growing when the
air in the cloud reaches the
same temperature as the air surrounding the cloud
 Water vapor releases energy (heat) as it condenses.
 The released of heat is very important to the formation of clouds.
o Rising dry air cools faster than rising moist air.
o Moist air cools more slowly due to the fact that heat is being release by
condensing water vapor.
o Heat released during ________________condensation can fuel the
growth of huge cumulonimbus clouds.
Cumulonimbus Clouds
 Cumulonimbus clouds form as moist air rises and cools to its dew point
(condensation level).
 Heat released from the condensation keeps the air rising.
 Air inside the cloud air is warmer and less dense than the air outside.
 Cumulus clouds that receives a continuous supply of warm moist air, it will
continue to grow until it enters a layer of stable air.
 Stable air is where the surrounding air temperture is the same as inside the cloud.
Layer Clouds
 Stratiform or layered clouds form in stable air.
o Air that cannot easily move up or down in stable air so the clouds will
spread out horizontally.
 Clouds for in stable air in two way:
1. Air is forced slowly upward to its condensation level. This happens when
air moves up a mountainside or over a layer of colder denser air or a low
pressure forces it upward.
2. Air cools past its condensation level by radiating heat or mixing with
cooler air.
Summary:
Essential Question:
Predicting Condensation Level
 As air rises the temperature and dew point decreases
 Condensation level can be determined by knowing the ground temperature and
dew point.
 Knowing the condensation level allows for
o predicting at what level clouds will form
o predicting how high they will grow
o predicting the severity of a possible storm
Precipitation
 Precipitation is any form of water that has formed in clouds and has grown heavy
enough to fall to Earth.
 Water droplets grow by
o bumping into and combing with other water droplets.
o The larger the droplets the faster they will fall.
 temperatures in upper clouds is below freezing,
o both ice and supercooled droplets form in the clouds.
o supercooled droplets evaporate and deposits on the ice crystals causing
them to grow.
 There are several forms of precipitation:
o Drizzle, Rain, Snow
o Sleet: rain freezes as it falls
o Freezing Rain: rain freezes as it hits a cold surface
o Hail: balls or irregular clumps of ice
 In the summer, frozen precipitation melts before hitting the ground except for
Hail.
o Hailstones begin as a frozen raindrop or small, dense clump of ice
crystals.
o Strong updrafts cause hailstones to grow until it is too heavy to stay
aloft.
o The stronger the updrafts the larger the hailstones.
Where does precipitation occur
 rising and cooling moist air major cause of precipitation
 warmer the air is before it rises the more moisture it can hold
 the higher it rises the more precipitation it can release.
 Areas that receive the most precipitation are those where warm moist air rises
high in large quantities.
o Near the equator due to heating of the land by insolation, causing
warmed air to rise. Daily thunderstorms
Summary:
Essential Question:
o
o
Summary:
Low pressure areas which cause air to rise and cool to produce
precipitation.
Areas where moist air often blows across a mountain range,
 The windward side receives precipitation as the air rises and
cools. It can receive large amounts of precipitation.
 The leeward side the colder and dryer air is sinking and warming
so there is little to no precipitation on this side of mountain
ranges (desert regions occur on the leeward side of a mountain
range).