Download Chapter 8: Weather

 The
sun hits different parts of the earth at
different angles
 Areas around the equator are hottest-sun
hits at a high angle
 Areas around the north and south pole are
the coldest-sun hits at a low angle
 The greater the angle of insolation, the
warmer it gets
 During the seasons, different parts of the
world are warm, while the other is cold
 Areas
of earth which receive more
concentrated sunlight are warm
 Areas of earth which receive spread out
sunlight are cold
 Time of day affects insolation
 By
measuring the angle at which the sun’s
rays hit earth we can see how the time of
day affects insolation
 We does this by looking at the shadows cast
by objects
 Shadows tell you the position of the sun
 The lower the angle, the longer the shadows
 Sunlight is most direct at midday
 The angle of insolation is less before and
after midday
Dark
colors absorb more heat than
light colors
Rough textures cause light to bounce
around, allowing more heat to be
absorbed
 Atmosphere
is the air that surrounds Earth
 Atmosphere ranges from the Earth’s surface
to the edge of space
 Layer closest to the Earth is the troposphere
 Troposphere is the narrowest layer
 All life exists in this layer
 All storms form in the troposphere
 In the troposphere, as altitude increases, the
temperature decreases
 As you enter the other layers the air thins
out
 Is
the force put on a given area by the
weight of the air above it
 Air is a mixture of gases
 Air is made mostly of nitrogen and oxygen
 Normal air pressure is greatest at sea level
 As altitude increases, air pressure
decreases
 This is because the height of the air column
above you becomes shorter
 The
weather is what the troposphere is like
at any given place and time
 Ex: It is rainy. Or It is windy. Or It is sunny.
 6 conditions make up the weather:
1. Air temperature
2. Air pressure
3. Amount of moisture in the air
4. Wind
5. Clouds
6. precipitation
 Use
a thermometer to measure temperature
 2 scales
1. Fahrenhreit (F)
2. Celsius (C)
 Air pressure is measured with a barometer
 2 types:
1. Mercury
2. Aneroid
 Water
vapor is water in the air
 Its in the form of a gas
 Its invisible, colorless, odorless and
tasteless
 Humidity is the amount of water vapor in the
air
 Water vapor gets into the air through
evaporation of H2O from oceans, rivers,
lakes and groundwater
 Condensation is when water vapor
molecules turn back into a liquid
2
factors determine the amount of humidity
in the air
1. There has to be water available to
evaporate
2. The warmer the temperature the faster the
water evaporates: this means warm air
takes on more water vapor than cold air
 Air has a limit on how much water it can
hold
 When
the air is full we say it is saturated
 When the air has very little water vapor we
say it is dry
 Relative humidity is a comparison between
how much water vapor is in the air and how
much it can hold
 It is given in percentages

1.
2.
3.
3 ways clouds form:
Air warms up by being pushed upward
over mountains by winds. This causes
clouds to form.
The sun heats cool air and it rises, forming
clouds
When cooler and warmer air meet, the
warmer air is pushed upward, causing
clouds to form
 Precipitation
is any form of water particles
that falls from the atmosphere and reaches
the ground
 Precipitation occurs when water droplets in
clouds become heavy enough to fall
 4 types:
1. Rain
2. Sleet
3. Snow
4. Hail
1.
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2.
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Rain
Condensation forms around nucleus
Cloud droplets collect
Falls through warm air
Sleet
Condensation forms around nucleus
Cloud droplets collect
Raindrop forms and falls through the air at
freezing temperatures
3.
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4.
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Snow
Condensation forms around ice nucleus
Supercooled water freezes around the ice
nucleus or water vapor changes to ice
crystals
Ice crystals grow and snowflakes form
The ground temperature is cold
Hail
Condensation forms around a nucleus
Cloud droplets freeze and collect around an
ice crystal
This process repeats over and over to form a
ball of ice
The ground temperature is warm
 Tall
clouds produce larger raindrops b/c
droplets run into each other and combine
 Large cumulus clouds have short, heavy
rain or snow storms
 Stratus clouds produce a long snow or rain
shower with small drops
 Clouds with a large vertical development
are very violent
 They produce great downpours and
sometimes even hail
 Hail
is produced by an updraft, which is a
wind that hurls ice crystals upward again
and again creating hail stones
 Cloud
cover is the amount of sky covered by
clouds
 We use the terms clear, scattered clouds,
partly cloudy, mostly cloudy or overcast
 Empty circle=clear
 Fully shaded circle=overcast
 ¼ shaded circle= scattered clouds
 ½ shaded circle=partly cloudy
 ¾ shaded circle=mostly cloudy
1.

2.
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3.
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Volume
When volume increases, pressure
decreases
Height above Earth’s surface
air pressure is higher at sea level b/c air
molecules are denser or closer together
Temperature
when air is heated it moves faster and
spreads out, decreasing the pressure
Cold air exerts more pressure
4.
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Amount of water vapor
Moist air exerts less pressure than dry air
b/c water vapor molecules are lighter than
nitrogen and oxygen molecules
Showing Air Pressure
/: represents rising air pressure
\ : represents falling air pressure
- : represents no change
It’s important to know if the air pressure is
changing b/c a falling barometer can be a
sign that a storm is coming
A rising barometer can be a sign fair
weather is approaching.
 Denser
air exerts a higher pressure than
less dense air
 Wind is air that moves horizontally
 Rising air is an updraft
 Sinking air is a downdraft
 cold air is denser than warm air
 Warm air has a low pressure
 Cold air has a high pressure
 Winds
are produced when air flows from a
area of higher pressure (cold air) to areas of
lower pressure (warm air)
 2 Types
1.

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of Breezes
Sea breeze
is a wind that blows from the sea to the land
Land air heats more quickly than the air
over the water, causing the warmer air to
rise and the cooler air replaces it
Air moves from higher pressure to a lower
pressure
2.
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Land Breeze
Blows from land to sea
Air over land cools more rapidly at night
Air moves from a higher pressure (cooler
air) to a lower pressure (warmer air)
 Is
named after Gustave Gaspard Coriolis
who described it in 1835
 Earth’s rotation affects winds blowing
across its surface
 Earth rotates counterclockwise
 In the Northern hemisphere the wind
always curves to the right
 In the southern hemisphere the winds
always curve to the left
 The
air near the equator is very warm,
moist and has a low pressure
 As the air moves away from the equator it
cools and becomes denser creating a highpressure zone
 Trade winds form at 30º N and 30º S
latitudes to the equator
 These winds are caused by air moving from
these high-pressure zones toward the low
pressure zone
 Polar
easterlies occur at 60º S and 60º N
latitudes to the poles
 Air at the poles is cold, dry and has a high
pressure
 These winds blow from the east
 Westerly Winds occur between 30º and 60º
N and S latitudes
 The winds blow from the west
 Knowing
where the air pressure is high or
low allows you to predict which way air will
move
 Maps are made to show air pressure
 An isobar is a line on a map that connects
places with equal air pressure
 They make pressure patterns easy to see
 In a high pressure system, winds blow in a
clockwise pattern out from the center, which
has the highest pressure
 In
a low pressure system, the center is
surrounded by higher pressure regions
 The winds blow in towards the center
counterclockwise
 Isobars help meteorologists predict how
fast air will move
 Big differences in air pressure over short
distances cause strong winds