Download Chapter 16-1 Study Guide (Weather)

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Chapter 16-1 - Weather Study Guide
Ms. Grady
What is weather?
 Daily conditions of the earth’s atmosphere.
Heating the Earth
 Meteorologists = people who study the weather.
 Weather = the daily condition of the Earth’s atmosphere.
 The atmospheric factors (reasons) that interact (act together) to cause
weather are:
-Heat energy
-Air pressure
-Winds
-moisture
Temperature
 Air temperature is a measure of the movement of the particles in the air.
 Wind = air that is moving from an area of high pressure to an area of
low pressure.
 The temperature of air can affect (change) air pressure.
 High (hot) temperature has lower air pressure then low (cold)
temperature.
 Wind speed can be measured with an anemometer.
anemometer
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Measuring Temperatures
 Air temperature is measured with a thermometer.
 Most thermometers consist (are made up of) a thin glass tube with a bulb
at one end.
 The bulb is filled with a liquid, usually mercury.
 Sometimes it is filled with a liquid such as alcohol that is colored with dye.
 When the temperature falls (goes down), the liquid then contracts (shrinks,
tightens, reduces). Therefore, it takes up less space and drops in the tube.
Air Pressure
 Air pressure = a measure of the force of the air pressing down on the
Earth’s surface.
 The air pressure at any point on the Earth is equal to the weight of the
air directly above that point.
 Air pressure at any particular point on the Earth depends on the
density (thickness) of the air.
 Denser (thicker) air has more mass per unit volume than less dense air.
So denser air exerts (uses) more air pressure.
Factors that Affect Air Pressure
 The density of the Earth’s atmosphere, and air pressure is affected (can
be changed) by three factors:
-temperature
-water vapor
-elevation
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 At a given pressure, moist air is less dense than dry air.
 This is because a water molecule has less mass than either a nitrogen or
an oxygen molecule.
 Therefore, air with a large amount of water vapor in it exerts
(uses/applies) less air pressure than drier air.
 As the elevation increases (goes up), the air becomes thinner, or less
dense. So the air pressure decreases with increasing elevation.
Mercury Barometer
 Air pressure is measured with an instrument called a barometer.
 There are 2 types of barometers:
- mercury
- aneroid
Mercury Barometer
 The open end of the glass tube is placed in a container of mercury.
At sea level it is supported at certain levels.
As the air pressure decreases, the column of mercury drops (goes
down)
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Aneroid Barometer
 An aneroid barometer consists of an airtight metal box from which
most of the air has been removed (taken out).
 A change in air pressure causes a needle to move along a dial, which
shows the new air pressure.
Aneroid Barometer
Humidity
Vocabulary
Water vapor = moisture
Humidity = water vapor or moisture in the air.
 The amount of moisture can vary (change) from place to place and
time to time.
Relative humidity = the percentage of moisture the air holds relative (in
relation) to the amount it could hold at a particular temperature.
When the relative humidity is 100%, the air is saturated.
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Psychrometer
 Meteorologists measure the relative humidity with a psychrometer.
 When the air pressure passes over the wet bulb, the water in the
cloth evaporates (dissolves or vanishes).
 Evaporation from the cloth cools the thermometer bulb.
 If the humidity is low, evaporation will take place quickly and the
temperature of the wet-bulb thermometer will drop (go down).
 If the humidity is high, the wet-bulb will not change much.
Relative humidity is determined by the difference between the two
and expressed as a percentage (%).
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Types of Clouds
Cumulus



Cumulonimbus
These clouds are

fluffy and white.
They form at

altitudes of 2.4 to
13.5 kilometers.
When you see
these clouds, they

usually show fair
weather.
Thunderstorm
clouds
High winds can
flatten the top of
the cloud into an
anvil-like shape.
When we see these
clouds, we may have
heavy rain, snow,
hail, lightning, and
possible tornadoes.
Stratus






Smooth, gray clouds
They cover the whole
sky and block out the
sun.
Form at an altitude of
about 2.5 km
Light rain and drizzle
Nimbostratus clouds
bring rain
Near the ground they
form fog
Fog
Stratus Grey clouds
Cirrus





Feathery
clouds
Fibrous clouds
(thin and string
like clouds)
Usually made
of ice crystals
Form at high
altitudes.
When you see
these clouds,
rain or snow
will most likely
fall within
several hours.
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Precipitation = Water that falls from the atmosphere to the Earth.
Water vapor that condenses (contracts, shrinks) and forms clouds can fall to
the Earth as:
 Rain
 Sleet
 Snow
 Hail
Types of Precipitation
Sleet
Snow
 Falling snow or rain  Water vapor (gas)
passes through an
changes directly into
extremely cold layer
a solid (ice).
of air → they freeze  Snowflakes are 6
into small ice pellets
sided ice crystals
(sleet)
(flakes)
 All snowflakes are
 Winter →sleet
different. No two
reaches the Earth
snowflakes are
exactly the same.
Hail
 Hail is one of the most
damaging forms of
precipitation in
cumulonimbus clouds.
 Hailstones =small balls
of ice (ranging from
5-75 mm in diameter)
 They form when water
droplets hit ice pellets
in a cloud and freeze.