Unit 5: Chapters 22, 23, 24, 25, and 3
WEATHER AND
CLIMATE
SES5. Students will investigate the
interaction of insolation and Earth
systems to produce weather and climate.
 a. Explain how latitudinal variations in solar heating create
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atmospheric and ocean currents that redistribute heat globally.
b. Explain the relationship between air masses and the surfaces
over which they form.
c. Relate weather patterns to interactions among ocean currents,
air masses, and topography.
d. Describe how temperature and precipitation produce the
pattern of climate regions (classes) on Earth.
e. Describe the hazards associated with extreme weather events
and climate change (e.g., hurricanes, tornadoes, El
Niño/La Niña, global warming).
f. Relate changes in global climate to variation in Earth/Sun
relationships and to natural and anthropogenic
modification of atmospheric composition.
Chapter 3
MODELS OF EARTH
Finding Locations on Earth:
Latitude
 A reference grid that is made up of additional
circles is used to locate places on Earth‘s surface.
 Halfway between the poles, a circle called the
equator divides Earth into the North and Southern
Hemispheres.
 parallel any circle that runs east and west around
Earth and that is parallel to the equator; a line of
latitude
 latitude the angular distance north or south from
the equator; expressed in degrees
Latitude
Degrees of Latitude
 Latitude is measured in degrees
 the equator is 0° latitude.
 the latitude of both the North Pole and the
South Pole is 90°.
 In actual distance, 1° latitude equals about
111 km.
Minutes and Seconds
 Each degree of latitude consists of 60 equal
parts, called minutes. One minute (symbol:
°) of latitude equals 1.85 km.
 Each minute is divided into 60 equal parts,
called seconds (symbol: °).
Longitude
 East-west locations are established by using
meridians.
 meridian any semicircle that runs north and
south around Earth from the geographic North
Pole to the geographic South Pole; a line of
longitude
 longitude the angular distance east or west
from the prime meridian; expressed in degrees
Longitude
Degrees of Longitude
 prime meridian - 0° longitude and passes
through Greenwich, England
 International Date Line - The meridian
opposite the prime meridian, halfway around
the world, is labeled 180°.
Distance Between Meridians
 The distance covered by a degree of
longitude depends on where the degree is
measured. The distance measured by a
degree of longitude decreases as you move
from the equator toward the poles.
Chapter 22
THE ATMOSPHERE
Characteristics of the Atmosphere
 Atmosphere – layer of gases that surrounds
Earth.
 Composition
 Most abundant elements in air are Nitrogen,
Oxygen, and Argon
 Nitrogen makes up 78% of Earth’s atmosphere
 Oxygen makes up 21% of Earth’s atmosphere
 Two most abundant compounds in air are CO2 and
H2O.
 Ozone (O3) in the Atmosphere
 Ozone layer found in upper layer of the
atmosphere and absorbs harmful ultraviolent
radiation from the sun.
 Damage to Ozone layer caused by release of
Chlorofluorocarbons (CFCs), previously used in
refrigerators and air conditioners, and nitrogen
oxide from exhaust.
 Particulates in the Atmosphere
 Tiny solid particles which may include
volcanic dust, ash from fires, microscopic
organisms, mineral particles lifted from soil
by winds, pollen from plants, etc.
Atmospheric Pressure
 Gases are held near the Earth’s surface by gravity
 99% of the total mass of the atmosphere is held within
32km of Earth’s surface
 Air molecules are compressed together and exert a
force on any surface.
 Pressure decreases as altitude increases
 The pull of gravity is not as strong at higher altitudes, so
the molecules are farther apart and exert less pressure
 Measured with a barometer
 Average atmospheric pressure at sea level is 1
atmospheres (atm)
Layers of the Atmosphere
Distinctive
pattern of
temperature
changes with
increasing
altitude
caused by
differences in
absorption of
solar energy.
 Troposphere
 Closest to Earth’s surface
 Extends to nearly 12km
 Contains all water and carbon dioxide
 All weather occurs here
 Air is heated by thermal energy radiated
from Earth’s surface
 Temperature decreases with altitude
 Stratosphere
 Extends to nearly 50km
 Contains almost all of the ozone
 Temperature increases with altitude as
ozone absorbs solar radiation
 Mesosphere
 Extends to about 80km
 Temperature decreases with altitude to nearly
-90°C
 Thermosphere
 Temperature increases with altitude because nitrogen and
oxygen absorb solar radiation
 Temperatures recorded at more than 1,000°C
 Contains the Ionosphere
 Atoms of gas molecules lose electrons producing ions and
free electrons.
 Reactions between solar radiation and ionosphere
produce auroras.
Solar Energy and the Atmosphere
 Radiation – all forms of energy that travel through
space as waves known as the Electromagnetic
Spectrum
 As solar radiation passes through the
atmosphere
 Shorter wavelengths (X-rays, gamma rays, and
ultraviolet rays) are absorbed in the upper
atmosphere
 Longer wavelengths (infrared and visible light) that
reach the lower atmosphere are absorbed by carbon
dioxide, water vapor, and other molecules in the
troposphere.
 Scattering occurs when particles and gas molecules
reflect and bend solar rays changing their direction,
but not wavelength
 Causes the sky to be blue and the sun to be red at
sunrise and sunset.
 When solar radiation reaches Earth’s surface, it is
either absorbed or reflected depending on the color,
texture, composition, volume, mass, transparency,
state of matter, and specific heat of the material.
 Albedo is the solar radiation that is reflected by
earth’s surface.
 30% of the solar energy that reaches Earth’s atmosphere
is reflected or scattered
 Earth’s albedo is 0.3
 Snow and ice reflect 50 to 90%
 Forests reflect 5 to 10%
 Surfaces heated by incoming solar radiation
convert the energy into infrared rays of longerwavelengths and reemit it.
 Those wavelengths of infrared rays are absorbed
by carbon dioxide, water vapor, and other gas
molecules in the atmosphere.
 This absorption and release of energy keeps the
earth’s surface warmer than it would be without
an atmosphere and is known as the Greenhouse
Effect
 Greenhouse Effect
Greenhouse Gases: naturally occurring gases that
absorb solar radiation quickly, but release it slowly.
H2O
CO2
Ozone
Methane
Human Impact on the Greenhouse
Effect
 Amount of Carbon Dioxide in the atmosphere
has been increasing due to burning fossil fuels
 Increases in Carbon Dioxide is believed to be
directly proportional to increase in energy
absorption by the atmosphere and increase in
global temperature.
 Temperature Variations
 Temperature of the atmosphere depends on
 Latitude
 Affects the angle the sun’s rays strike an area
 Energy that reaches the equator is at 90° angle and
is more intense than at lower latitudes
 Surface features
 Determines the amount of energy absorbed,
reflected and reradiated.
 Time of year and day
 Tilt of the Earth’s axis determines seasons as the
hemisphere tilted toward the sun receives direct,
more intense energy from the sun
 Water Vapor in the Air and Surface absorbs
and holds energy
 Water has high specific heat. It requires a lot of
energy to increase its temperature, but will take a
long time to cool down.
 Areas having less water vapor, such as deserts,
tend to warm during the day but cool very quickly
at night.
 Areas with high quantities of water vapor, such as
near large bodies of water, generally have more
moderate temperatures as the water vapor
absorbs and holds the sun’s energy.
Transfer of Energy
 Conduction
 Transfer by direct contact
 Lowest few centimeters of the atmosphere are
heated by conduction
 Convection
 Transfer within a liquid or a gas
 Less dense gas or liquid rises, more dense
sinks creating convection currents.
 Creates ocean currents and wind
Atmospheric Circulation
 Pressure differences in the atmosphere cause
the movement of air
 Air near the surface generally flows from the
high-pressure, cold, poles toward the lowerpressure, warm, equator.
 Coriolis Effect - the tendency of a moving object
to follow a curved path rather than a straight
path because of the Earth’s rotation.
 Northern Hemisphere – currents curve to the right, or
clockwise
 Southern Hemisphere – currents curve to the left, or
counterclockwise
 Coriolis Effect
 Global Winds
 Convection cells - 3 looping patterns of air flow in each
hemisphere create wind belts, also known as prevailing
winds
•Trade Winds –
flow toward the
equator
•Westerlies – flow
in the
mid-latitudes
•Polar Easterlies
 Wind and Pressure Shifts
 As the sun’s rays shift during changing seasons, the
position of pressure belts and wind belts shift.
 Example: The westerlies prevail in Southern Florida
during the winter, but trade winds dominate in the
summer.
 Jet Streams
 Narrow bands of high-speed winds that blow in the
upper troposphere and lower stratosphere
 Sometimes 100km wide and 2 to 3 km thick reaching
speeds of 500km/h
 Affect airline routes and storm paths
 Local Winds
 Influenced by local temperature variations
 Gentle winds that extend over less than 100km.
 Land Sea Breezes
 Land surfaces heat up faster than water surfaces. Air over
land warms, rises, and cool air over water moves in to
replace it.
 Reverses at night as land surfaces cool faster than water.
 Mountain and Valley Breezes
 Warm air from the valley moves upward during the day
 At night, cool air descends from the mountain peaks and
settles in the valley
Chaper 23
WATER IN THE
ATMOSPHERE
Chapter 23
Changing Forms of Water
 Water in the atmosphere exists in three states,
or phases.
 One phase is known as a gas called water vapor.
 The other two phases of water are the solid
phase known as ice and the liquid phase known
as water.
 Water changes from one phase to another when
heat energy is absorbed or released.
Chapter 23
Changing Forms of Water, cont.
Latent Heat
latent heat the heat energy that is absorbed or
released by a substance during a phase
change
 When liquid water evaporates, the water
absorbs energy from the environment.
 When water vapor changes back into a liquid
through the process of condensation, energy
is released into the surrounding air and the
molecules move closer together.
Chapter 23
Changing Forms of Water, cont.
Evaporation
 Most water enters the atmosphere through
evaporation of ocean water near the equator.
 However, water vapor also enters the
atmosphere by evaporation from lakes,
ponds, streams, and soil.
 Plants release water into the atmosphere in a
process called transpiration.
 Volcanoes and burning fuels also release
small amounts of water vapor into the
atmosphere.
Chapter 23
Changing Forms of Water, cont.
Sublimation
sublimation the process in which a solid
changes directly into a gas (the terms is
sometimes used for the reverse process)
 Ice commonly changes into a liquid before
changing into a gas.
 When the air is dry and the temperature is
below freezing, ice and snow may sublimate
into water vapor.
Chapter 23
Changing Forms of Water, cont.
The diagram below shows the different phases of water.
Chapter 23
Humidity
 Water vapor in the atmosphere is known as
humidity.
 Humidity is controlled by rates of
condensation and evaporation.
 When the rate of evaporation and the rate of
condensation are in equilibrium, the air is said
to be “saturated.”
Chapter 23
Humidity, continued
 The rate of evaporation is determined by the
temperature of the air.
 The higher the temperature is, the higher the
rate of evaporation is.
 The rate of condensation is determined by
vapor pressure.
 When vapor pressure is high, the
condensation rate is high.
Chapter 23
Humidity, continued
Absolute Humidity
absolute humidity the mass of water vapor per
unit volume of air that contains the water
vapor, usually expressed as grams of water
vapor per cubic meter of air
absolute humidity =
mass of water vapor (grams)
volume of air (cubic meters)
Chapter 23
Humidity, continued
Absolute Humidity, continued
 However, as air moves, its volume changes as
a result of temperature and pressure
changes.
 Therefore, meteorologists prefer to describe
humidity by using the mixing ratio of air.
 The mixing ratio of air is the mass of water
vapor in a unit of air relative to the mass of
the dry air.
Chapter 23
Humidity, continued
The diagram below shows the effects of vapor pressure.
Chapter 23
Humidity, continued
Relative Humidity
relative humidity the ratio of the amount of water
vapor in the air to the amount of water vapor
needed to reach saturation at a given
temperature
 If the temperature does not change, the relative
humidity will increase if moisture enters the air.
 Relative humidity can also increase if the
moisture in the air remains constant but the
temperature decreases.
Chapter 23 Humidity,
Measuring
continued
Using Psychrometers to Measure Humidity
 It consists of two identical thermometers. The
bulb of one thermometer is covered with a damp
wick, while the bulb of the other thermometer
remains dry.
 When the psychrometer is held by a handle and
whirled through the air, the air circulates around
both thermometers.
 The difference between the dry-bulb
temperature and the wet-bulb temperature is
used to calculate relative humidity.
Changing Forms of Water,
cont.
Dew point at constant pressure and water
vapor content, the temperature at which
the rate of condensation equals the rate of
evaporation
Chapter 23 continued
Humidity,
Reaching the Dew Point
 When the air is nearly saturated with a
relative humidity of almost 100%, only a
small temperature drop is needed for air to
reach its dew point.
 Air may cool to its dew point by conduction
when the air is in contact with a cold surface.
 The resulting form of condensation is called
dew.
Chapter 23
Humidity, continued
Reaching the Dew Point, continued
 If dew point falls below the freezing
temperature of water, water vapor may
change directly into solid ice crystals, or frost.
 Because frost forms when water vapor turns
directly into ice, frost is not frozen dew.
 Frozen dew is relatively uncommon. Unlike
frost, frozen dew forms as clear beads of ice.
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How Do Clouds Stay Up?
https://www.youtube.com/watch?v=DjByja9ejTQ
Clouds and Weather (3:21)
https://www.youtube.com/watch?v=hJ6aeSv8xIU
Types of Clouds 5:05
https://www.youtube.com/watch?v=FMagDRCpJ14
Clouds and Weather 3:21
https://www.youtube.com/watch?v=hJ6aeSv8xIU
Rare Cloud Formations 3:05
https://www.youtube.com/watch?v=wiFyg0i9K3M
Chapter 23
Cloud Formation
cloud a collection of small water droplets or ice
crystals suspended in the air, which forms
when the air is cooled and condensation
occurs
 For water vapor to condense and form a
cloud, a solid surface on which condensation
can take place must be available.
 In addition, for clouds to form, the rate of
evaporation must initially be in equilibrium
with the rate of condensation.
Chapter 23
Cloud Formation, continued
condensation nucleus a solid particle in the
atmosphere that provides the surface on
which water vapor condenses
 Although the lowest layer of the atmosphere,
the troposphere, does not contain any large
solid surfaces, it contains millions of
suspended particles of ice, salt, dust, and
other materials.
 Because the particles are so small—less than
0.001 mm in diameter—they remain
suspended in the atmosphere for a long time.
Chapter 23
Cloud Formation, continued
The diagram below shows the molecular formation of a water droplet.
Chapter 23
Adiabatic Cooling
adiabatic cooling the process by which the
temperature of an air mass decreases as the
air mass rises and expands
 As a mass of air rises, the surrounding
atmospheric pressure decreases.
 Thus, fewer collisions between the molecules
happen.
 The resulting decrease in the amount of
energy that transfers between molecules
decreases the temperature of the air.
Chapter 23
Adiabatic Cooling, continued
Adiabatic Lapse Rate
 The rate at which the temperature of a parcel
of air changes as the air rises or sinks is called
the adiabatic lapse rate.
 The adiabatic lapse rate of clear air is about –
1°C per 100 m that the air rises.
 The slower rate of cooling of moist air results
from the release of latent heat as the water
condenses.
Chapter 23
Adiabatic Cooling, continued
Condensation Level
 When air cools to a temperature that is below
the dew point, net condensation causes clouds
to form.
 The altitude at which this net condensation
begins is called the condensation level.
 The condensation level is marked by the base of
the clouds.
 Further condensation allows clouds to rise and
expand above the condensation level.
Chapter 23
Mixing
 Some clouds form when one body of moist
air mixes with another body of moist air that
has a different temperature.
 The combination of the two bodies of air
causes the temperature of the air to change.
 This temperature change may cool the
combined air to below its dew point, which
results in cloud formation.
Chapter 23
Lifting
 Air can be forced upward when a moving
mass of air meets sloped terrains, such as a
mountains range.
 As the rising air expands and cools, clouds
form.
 The large cloud formations associated with
storm systems also form by lifting.
 These clouds form when a mass of cold,
dense air enters an area and pushes a less
dense mass of warmer air upward.
Chapter 23
Advective Cooling
advective cooling the process by which the
temperature of an air mass decreases as the
air mass moves over a cold surface
 As air moves over a surface that is colder than
air is, the cold surface absorbs heat from the
air and the air cools.
 If the air cools below its dew point, clouds
form.
Chapter 23
Classification of Clouds
 Clouds are classified by their shape and
their altitude.
 The three basic cloud forms are stratus
clouds, cumulus clouds, and cirrus clouds.
 There are also three altitude groups: low
clouds (0-2,000 m), middle clouds (2,000
to 6,000 m), and high clouds (above 6,000
m).
Chapter 23
Classification of Clouds,
continued
Stratus Clouds
stratus cloud a gray cloud that has a flat uniform
base and that commonly forms at very low
altitudes
 Stratus means “sheet-like” or “layered.”
 Stratus clouds form where a layer of warm,
moist air lies above a layer of cool air.
 Stratus clouds cover large areas of sky and often
block out the sun.
Stratus Clouds
Chapter 23
Classification
of Clouds,
continued
Stratus Clouds, continued
 The two variations of stratus clouds are
known as nimbostratus and altostratus.
 Unlike other stratus clouds, the dark
nimbostratus clouds can cause heavy
precipitation.
 Altostratus clouds form at middle altitudes.
They are generally thinner than the low
stratus clouds and produce very little
precipitation.
Chapter 23
Classification
of Clouds,
continued
Cumulus Clouds
cumulus cloud a low-level, billowy cloud that
commonly has a top that resembles cotton balls
and has a dark bottom
 Cumulus means “piled” or “heaped.”
 These clouds form when warm, moist air rises
and cools. As the cooling reaches its dew point,
the clouds form.
 The flat base that is characteristic of most
cumulus clouds represents the condensation
level.
Cumulus Clouds
Chapter 23
Classification
of Clouds,
continued
Cumulus Clouds, continued
 High, dark storm clouds known as cumulonimbus
clouds, or thunderheads, are often accompanied
by rain, lightning, and thunder.
 If the base of cumulus clouds begins at middle
altitudes, the clouds are called altocumulus
clouds.
 Low clouds that are a combination of stratus and
cumulus clouds are called stratocumulus clouds.
Chapter 23
Classification
of Clouds,
continued
Cirrus Clouds
cirrus cloud a feathery cloud that is composed
of ice crystals and that has the highest
altitude of any cloud in the sky
 Cirro– and cirrus mean “curly.”
 Cirrus clouds form at altitudes above 6,000
m. These clouds are made of ice crystals
because the temperatures are low at such
high altitudes.
 Because these clouds are thin, light can easily
pass through them
Cirrus Clouds
Chapter 23
Classification
of Clouds,
continued
Cirrus Clouds, continued
 Cirrocumulus clouds are rare, high-altitude,
billowy clouds composed entirely of ice crystals.
Cirrocumulus clouds commonly appear just
before a snowfall or a rain fall.
 Long, thin clouds called cirrostratus clouds form a
high, transparent veil across the sky.
 A halo may appear around the sun or moon
when either is viewed through a cirrostratus
cloud.
Chapter 23
Classification
of Clouds,
continued
The diagram below shows the different types of clouds in the atmosphere.
Chapter 23
Fog
fog water vapor that has condensed very near
the surface of Earth because air close to the
ground has cooled
 The obvious difference between fog and
clouds is that fog is very near the surface of
Earth.
 However, fog also differs from clouds
because of how fog forms.
Chapter 23
Fog, continued
Radiation Fog
 One type of fog forms from the nightly cooling
of Earth.
 The layer of air in contact with the ground
becomes chilled to below the dew point, and the
water vapor in that layer condenses into
droplets.
 This type of fog is called radiation fog because it
results from the loss of heat by radiation.
Chapter 23
Fog, continued
Other Types of Fog
 Another type of fog, advection fog, forms when
warm, moist air moves across a cold surface.
Advection fog is common along coasts, where
warm, moist air from above the water moves in
over a cooler land surface.
 An upslope fog forms by the lifting and cooling of
air as air rises along land slopes.
 Steam fog is a shallow layer of fog that forms
when cool air moves over an inland warm body
of water, such as a river.
Chapter 23
Precipitation
precipitation any form of water that falls to
Earth’s surface from the clouds; includes rain,
snow, sleet, and hail
 The four major types of precipitation are rain,
snow, sleet, and hail.
Chapterof
23 Precipitation
Forms
 Rain is a liquid precipitation.
 If the raindrops are smaller than 0.5 mm, the
rain is called drizzle.
 The most common form of solid precipitation
is snow, which consists of ice particles.
 These particles may fall as small pellets, as
individual crystals, or as crystals that combine
to form snowflakes.
Chapter 23
Forms of Precipitation,
continued
 When rain falls through a layer of freezing air
near the ground, clear ice pellets, called sleet,
can form.
 In some cases, the rain does not freeze until it
strikes a surface near the ground. There, it forms
a thick layer of ice called glaze ice.
 Hail is a solid precipitation in the form of lumps
of ice. Hail usually forms in cumulonimbus
clouds.
Chapter 23
Causes
of Precipitation
 Most cloud droplets have a diameter of about
20 micrometers, which is smaller than the
period at the end of this sentence.
 A droplet must increase in diameter by about
100 times to fall as precipitation.
 Two natural processes cause cloud droplets to
grow large enough to fall as precipitation:
coalescence and supercooling.
Chapter 23
Causes of Precipitation,
continued
coalescence the formation of large droplets by
the combination of smaller droplets
 Larger droplets fall much faster through the
air than small ones do.
 As these large droplets drift downward, they
collide and combine with smaller droplets.
 Each large droplet continues to coalesce until
it contains a million times as much water as it
did originally.
Chapter 23
Causes
of Precipitation,
continued
supercooling a condition in which a substance
is cooled below its freezing point,
condensation point, or sublimation point,
without going through a change of state
 Supercooled water droplets cannot freeze
because too few freezing nuclei on which ice
can form are available.
 Freezing nuclei are solid particles that are
suspended in the air and that have structures
similar to the crystal structure of ice.
Chapter 23
Causes
of Precipitation,
continued
 Most water from the supercooled water droplets
evaporates.
 The water vapor then condenses on the ice
crystals that have formed on the freezing nuclei.
 The ice crystals rapidly increase in size until they
gain enough mass to fall as snow.
 If the ice crystals melt and turn into rain as they
pass through air whose temperature is above
freezing, they form the big raindrops that are
common in summer thunderstorms.
Chapter 23
Measuring Precipitation
Amount of Precipitation
 In one type of rain gauge, rainwater passes
through a funnel into a calibrated container,
where the amount of rainfall can then be
measured.
 Snow depth is simply measured with a
measuring stick.
 The water content of the snow is determined by
melting a measured volume of snow and by
measuring the amount of water that results.
Chapter 23
Measuring Precipitation,
continued
Doppler Radar
 The intensity of precipitation can be measured
using Doppler radar. Doppler radar images are
commonly used by meteorologists for
communicating weather forecasts.
 Doppler radar works by bouncing radio waves off
rain or snow.
 By timing how long the wave takes to return,
meteorologist can detect the location, direction
of movement, and intensity of precipitation.
Chapter 23Modification
Weather
cloud seeding the process of introducing
freezing nuclei or condensation nuclei into a
cloud in order to cause rain to fall
 In areas suffering from drought, scientists
may attempt to induce precipitation through
cloud seeding.
Chapter 23
Weather Modification,
continued
Methods of Cloud Seeding
 One method of cloud seeding uses silver iodide
crystals, which resemble ice crystals, as freezing
nuclei.
 Another method of cloud seeding uses
powdered dry ice, which is dropped from aircraft
to cool cloud droplets and cause ice crystals to
form.
 As ice crystals fall, they may melt to form
raindrops.
Chapter 23
Weather Modification,
continued
Improving Cloud Seeding
 Thus, meteorologists have concluded that cloud
seeding may increase precipitation under some
conditions but decrease it under others.
 Eventually, cloud seeding may become a way to
overcome many drought-related problems.
 Cloud seeding could also help control severe
storms by releasing precipitation from clouds
before a storm can become too large.
Chapter 24
WEATHER
Chapter 24
Air Masses
 Differences in air pressure are caused by
unequal heating of Earth’s surface.
 The equator receives more solar energy than
the poles do.
 Cold air near the pole sinks and creates highpressure centers.
 Differences in air pressure at different
locations on Earth create wind patterns.
Air Pressure
 Differences in air pressure are caused by
unequal heating of the Earth’s surface.
 Warmer air is less dense and has a lower
pressure
 Colder air is more dense and has a
greater pressure
Chapter 24
How Air Moves
 Air moves from areas of high pressure to
areas of low pressure. Therefore, there is a
general, worldwide movement of surface air
from the poles toward the equator.
 Temperature and pressure differences on
Earth’s surface create three wind belts in the
Northern Hemisphere and three wind belts in
the Southern Hemisphere.
 The Coriolis effect, which occurs when winds
are deflected by Earth’s rotation, also
influences wind patterns.
Wind – moving air
 Created by differences in pressure
 Coriolis effect causes winds to travel in a
curved path .
 Winds in the Northern Hemisphere turn
right
 Winds in the Southern Hemisphere turn
left.
Global Winds
The diagram below shows the different wind belts on Earth.
• Polar easterlies
60 ° - 90 ° latitude
• Westerlies
30 ° -60 ° latitude
• Tradewinds
equator to 30° latitude
Chapter 24
Formation of Air Masses
air mass a large body of air throughout which
temperature and moisture content are similar
 Small air pressure differences, air remains
relatively stationary.
 Slow moving air takes on characteristic
temperature and humidity of that region.
 Air masses that form over frozen polar
regions are very cold and dry.
 Air masses that form over tropical oceans are
warm and moist.
Chapter 24
Types of Air Masses
 Air masses are classified according to their
source regions.
 Polar regions form cold air masses. Tropical
areas forms warm air masses.
 Air masses that form over the ocean are
called maritime. Air masses that form over
land are called continental.
 The combination of tropical or polar air and
continental or maritime air results in air
masses that have distinct characteristics.
Chapter 24
Types of Air Masses,
continued
Continental Air Masses
 There are two types of continental air masses:
1. continental polar (cP)
 cold and dry.
2. continental tropical (cT).
 warm and dry.
 An air mass will eventually move into other
regions because of global wind patterns.
Chapterof
24 Air Masses,
Types
continued
Maritime Air Masses
The two different maritime air masses
1. maritime polar (mP)
 moist and cold.
2. maritime tropical (mT).
 moist and warm
 When these very moist masses of air travel
to a new location, they commonly bring
more precipitation and fog
Chapter 24
North American Air Mass
 The four types of air masses that affect
the weather of North America come from
six regions.
 An air mass usually brings the weather of
its source region, but an air mass may
change as it moves away from its source
region.
 For example, cold, dry air may become
warm and more moist as it moves from
land to the warm ocean.
Chapter 24
Types of Air Masses,
continued
The diagram below shows the four types of air mass that influence North
America.
Chapter 24
Fronts
 A cool air mass is dense and does not mix
with the less-dense air of a warm air mass.
 Thus, a boundary, called a front, forms
between air masses.
 Changes in middle-latitude weather usually
take place along the various types of fronts.
 Fronts do not exist in the Tropics because no
air masses that have significant temperature
differences exist there.
Chapter 24
Fronts, continued
Cold Fronts
cold front the front edge of a moving mass of
cold air that pushes beneath a warmer air
mass like a wedge
 If the warm air is moist, clouds will form.
Chapter 24
Fronts, continued
Cold Fronts, continued
 Large cumulus and cumulonimbus clouds
typically form along fast-moving cold
fronts.
 A long line of heavy thunderstorms, called a
squall line, may occur in the warm, moist air
just ahead of a fast-moving cold front.
 A slow-moving cloud front typically
produces weaker storms and lighter
precipitation than a fast-moving cold front
does.
Chapter 24 continued
Fronts,
Warm Fronts
warm front the front edge of advancing warm air
mass that replaces colder air with warmer air
 The slope of a warm front is gradual.
 Because of this gentle slope, clouds may extend
far ahead of the surface location, or base, of the
front.
 A warm front generally produces precipitation
over a large area and may cause violent weather.
Chapter 24 continued
Fronts,
Stationary and Occluded Fronts
stationary front a front of air masses that
moves either very slowly or not at all
occluded front a front that forms when a cold
air mass overtakes a warm air mass and lifts
the warm air mass of the ground and over
another air mass
 Sometimes, when air masses meet, the cold
moves parallel to the front, and neither air
mass is displaced.
Chapter 24
Weather Map of the
United States
ChapterFronts
24
Polar
and
Midlatitudes Cyclones
midlatitude cyclone an area of low pressure that is characterized by
rotating wind that moves toward the rising air of the central lowpressure region
 Over each of Earth’s polar regions is a dome of cold air that may
extend as far as 60° latitude.
 The boundary where this cold polar air meets the tropical air mass of
the middle latitudes, especially over the ocean, is called the polar
front.
 Waves are the beginnings of low-pressure storm centers called
midlatitude cyclones or wave cyclones.
 These cyclones strongly influence weather patterns in the middle
latitudes.
Chapter 24
Severe
Weather
Thunderstorms
thunderstorm a usually brief, heavy storm that
consists of rain, strong winds, lightning, and
thunder
 Form in cumulonimbus clouds
 The thunderstorm dissipates as the supply of
water vapor decrease.
Thunderstorm
Chapter 24
Severe Weather, continued
Lightning
 During a thunderstorm, clouds discharge
electricity in the form of lightning.
 The released electricity heats the air, and the
air rapidly expands and produces a loud noise
known as thunder.
 For lightning to occur, the clouds must have
areas that carry distinct electrical charges.
Lightning
Chapter 24
Severe
Weather, continued
Hurricanes
hurricane a severe storm that develops over
tropical oceans and whose strong winds of
more than 120 km/h spiral in toward the
intensely low-pressure storm center
 A hurricane begins when warm, moist air
over the ocean rises rapidly.
 When moisture in the rising warm air
condenses, a large amount of energy in the
from of latent heat is released. This heat
increase the force of the rising air.
Chapter 24
Severe
Weather, continued
Hurricanes, continued
 A fully developed hurricane consists of a series of
thick cumulonimbus cloud bands that spiral
upward around the center of the storm.
 The most dangerous aspect of a hurricane is a
rising sea level and large waves, called a storm
surge.
 Every hurricane is categorized on the SafirSimpson scale by using several factors. These
factors include central pressure, wind speed, and
storm surge.
Hurricane
Chapter 24
Severe Weather, continued
Tornadoes
tornado a destructive, rotating column of air
that has very high wind speeds and that
maybe visible as a funnel-shaped cloud
 The smallest, most violent, and shortest-lived
severe storm is a tornado.
 A tornado forms when a thunderstorm meets
high-altitude horizontal winds. These winds
cause the rising air in the thunderstorm to
rotate.
Chapter 24
Severe Weather, continued
Tornadoes, continued
 A storm cloud may develop a narrow, funnelshaped rapidly spinning extension that reaches
downward and may or may not touch the
ground.
 If the funnel does touch the ground, it generally
moves in a wandering, haphazard path.
 The destructive power of a tornado is due to
mainly the speed of the winds. These winds
may reach speeds of more than 400 km/h.
Tornado
Chapter 24 Lower-Atmospheric
Measuring
Conditions
Air Temperature
thermometer an instrument that measures and
indicates temperature
 A common type of thermometer uses a liquid—
usually mercury or alcohol—sealed in a glass
tube to indicate temperature.
 A rise in temperature causes the liquid to expand
and fill more of the tube. A drop in temperature
causes the liquid to contract and fill less of the
tube.
Chapter 24
Measuring Lower-Atmospheric
Conditions, continued
Air Temperature, continued
 Another type of thermometer is an electrical
thermometer.
 As the temperature rises, the electric current
that flows through the material of the
electrical thermometer increases and is
translated into temperature readings.
Thermometer
Chapter 24 Lower-Atmospheric
Measuring
Conditions, continued
Air Pressure
barometer an instrument that measures
atmospheric pressure
 Changes in air pressure affect air masses.
 The approach of a front is usually indicated by
a drop in air pressure.
Barometer
Chapter 24 Lower-Atmospheric
Measuring
Conditions, continued
Wind Speed
anemometer an instrument used to measure wind
speed
 A typical anemometer consists of small cups that
are attached by spokes to a shaft that rotates
freely.
 The wind pushes against the cup and causes
them to rotate. This rotation triggers an
electrical signal that registers the wind speed in
meters per second or in miles per hour.
Anemometer
Chapter 24
Measuring Lower-Atmospheric
Conditions, continued
Wind Direction
wind vane an instrument used to determine
direction of the wind
 The wind vane is commonly an arrow-shaped
device that turns freely on a pole as the tail
catches the wind.
 Wind direction may be described by using one of
16 compass directions, such as north-northeast.
Wind direction also may be recorded in degrees
by moving clockwise and beginning with 0° at
the north.
Wind Vane
Chapter 24
Measuring Upper-Atmospheric
Conditions
Radiosonde
radiosonde a package of instruments that is
carried aloft by balloons to measure upper
atmospheric conditions, including temperature,
dew point, and wind velocity
 The radiosonde sends measurements as radio
waves to a receiver that records the information.
 When the balloon reaches a very high altitude,
the balloon expands and bursts, and the
radiosonde parachutes back to Earth.
Radiosonde
Chapter 24 Upper-Atmospheric
Measuring
Conditions, continued
Radar
radar radio detection and ranging, a system that
uses reflected radio waves to determine the
velocity and location of objects
 For example, large particles of water in the
atmosphere reflect radar pulses.
 The newest Doppler radar can indicate the
precise location, movement,and extent of a
storm. It can also indicate the intensity of
precipitation and wind patterns within a storm.
Chapter 24
Measuring
Upper-Atmospheric
Conditions, continued
Weather Satellites
 Satellite images provide weather information for
regions where observations cannot be made
from ground.
 The direction and speed of the wind at the level
of the clouds can also be measured by examining
a continuous sequence of cloud images.
 Satellite instruments can also measure marine
conditions.
Chapter 24
Global Weather Monitoring
 Weather stations around the world exchange the
weather information they have collected.
 The World Meteorological Organization (WMO)
sponsors a program called World Weather Watch
to promote the rapid exchange of weather
information.
 It also offers advice on the effect of weather on
natural resource and on human activities, such as
farming and transportation.
Chapter 24
Weather Maps
Weather Symbols
station model a pattern of meteorological
symbols that represent the weather at a
particular observing station and that is
recorded on a weather map
 Common weather symbols describe cloud
cover, wind speed, wind direction, and
weather conditions, such as type of
precipitation and storm activity.
Chapter 24
Weather Maps, continued
Weather Symbols, continued
 Other information included in the station
model are the air temperature and the dew
point.
 The dew point indicates how high the
humidity of the air is, or how much water is in
the air.
 The station model also indicates the
atmospheric pressure by using a three-digit
number in the upper right hand corner.
Chapter 24
Section 4 Forecasting the Weather
Weather Maps, continued
The diagram below shows the different weather symbols used on weather
maps.
Chapter 24
Weather Maps, continued
Plotting Temperature and Pressure
 Lines that connect points of equal
temperatures are called isotherms.
 Lines that connect points of equal
atmospheric pressure are called isobars.
 The spacing and shape of the isobars help
meteorologists interpret their observations
about the speed and direction of the wind.
Chapter 24
Weather Maps, continued
Plotting Fronts and Precipitation
 Most weather maps mark the locations of
fronts and areas of precipitation.
 Fronts are identified by sharp changes in wind
speed and direction, temperature or
humidity.
 Areas of precipitation are commonly marked
by using colors or symbols.
Chapter 24
Weather Maps, continued
The diagram below shows an example of a typical weather map.
Chapter 24Forecasts
Weather
 To forecast the weather, meteorologists
regularly plot to the intensity and path of
weather systems on maps.
 Meteorologists then study the must recent
weather map and compare it with maps from
previous hours.
 By following the progress of weather
systems, meteorologist can forecast the
weather.
Chapter 24Forecasts, continued
Weather
Weather Data
 Computers models can show the possible
weather conditions for several days.
 Comparing models helps meteorologists
better predict weather.
 By using computers, scientists can
manipulate data on temperature and
pressure to simulate errors in measuring
these data.
Chapter 24
Weather Forecasts, continued
Severe Weather Watches and Warnings
 One main goal of meteorology is to reduce
the amount of destruction caused by severe
weather by forecasting severe weather early.
 A watch is issued when the conditions are
ideal for severe weather.
 A warning is given when severe weather has
been spotted or is expected within 24 hours.
Chapter 24
Controlling
the Weather
 Some meteorologists are investigating
methods of controlling rain, hail, and
lightning.
 Currently, the most researched method for
producing rain has been cloud seeding.
 Cloud seeding can also be used to prevent
more severe precipitation.
Chapter 24
Controlling
the Weather,
continued
Hurricane Control
 Hurricanes have also been seeded with freezing
nuclei in an effort to reduce the intensity of the
storm.
 During Project Stormfury, which took place
from 1962 to 1983, four hurricanes were
seeded, and the project had mixed results.
 Scientists have, for the most part, abandoned
storm and hurricane control because it is not an
attainable goal with existing technology.
Chapter 24
Controlling the Weather,
continued
Lightning Control
 Seeding of potential lightning storms with
silver-iodide nuclei has seemed to modify
the occurrence of lighting.
 However, no conclusive results have been
obtained.
Chapter 25
CLIMATE
Chapter 25
Temperature
and
Precipitation
climate the average weather conditions in an area
over a long period of time
 Climates are chiefly described using average
temperature and precipitation.
 Another way scientists describe climate is by
using the yearly temperature range, or the
difference between the highest and lowest
monthly averages.
 The factors that have the greatest influence on
both temperature and precipitation are latitude,
heat absorption and release, and topography.
Chapter 25
Latitude
Solar Energy
 The higher the latitude of an area is, the
smaller the angle at which the sun’s rays hit
Earth is and the smaller the amount of solar
energy received by the area is.
 Because Earth’s axis is tilted, the angle at
which the sun’s rays hit an area changes as
Earth orbits the sun.
Chapter 25
Latitude, continued
The diagram below shows the varying temperatures in the Northern
Hemisphere during winter.
Chapter 25 continued
Latitude,
Global Wind Patterns
 Because Earth receives different amounts of
solar energy at different latitudes, belts of cool,
dense air form at latitudes near the poles, while
belts of warm, less dense air form near the
equator.
 Winds affect many weather conditions, such as
precipitation, temperature, and cloud cover.
 Thus, regions that have different global wind
belts often have different climates.
Chapter 25
Latitude,
continued
Global Wind Patterns, continued
 As seasons change, the global wind belts shift
in a north or south direction.
 As the wind and pressure belts shift, the belts
of precipitation associated with them also
shift.
Chapter 25
Heat Absorption and Release
 Land heats faster than water and thus can reach
higher temperatures in the same amount of
time.
 Waves, currents, and other movements
continuously replace warm surface water with
cooler water from the ocean depths.
 In turn, the temperature of the land or ocean
influences the amount of heat that the air above
the land or ocean absorbs or releases.
 The temperature of the air then affects the
climate of the area.
Chapter
25
Heat
Absorption
and Release,
continued
Specific Heat and Evaporation
specific heat the quantity of heat required to
raise a unit mass of homogeneous material 1
K or 1°C in a specified way given constant
pressure and volume
 Even if not in motion, water warms more
slowly than land does.
 Water also releases heat energy more slowly
than land does.
Chapter
25
Heat
Absorption
and Release,
continued
Specific Heat and Evaporation, continued
 A given mass of water requires more energy
than land of the same mass does to
experience an increase in temperature of the
same number of degrees.
 The average temperature of land and water at
the same latitude also vary because of
differences in the loss of heat through
evaporation.
 Evaporation affects water surfaces much
more than it affects land surfaces.
Chapter 25
Heat Absorption and Release,
continued
Ocean Currents
 The temperature of ocean currents that come
in contact with the air influences the amount of
heat absorbed or released by the air.
 If winds consistently blow toward shore, ocean
currents have a strong effect on air masses over
land.
 For example, the combination of a warm
Atlantic current and steady westerly winds
gives northwestern Europe a high average
temperature for its latitude.
Chapter 25
Heat Absorption and Release,
continued
El Niño Southern–Oscillation
El Niño the warm-water phase of the El Niño
Southern Oscillation; a periodic occurrence in the
eastern Pacific Ocean in which the surface-water
temperature becomes unusually warm (ENSO)
 The event changes the interaction of the ocean
and the atmosphere, which can change global
weather patterns.
 The ENSO also has a cool-water phase called La
Niña, which also affects weather patterns.
Chapter
25
Heat
Absorption
and Release,
continued
Seasonal Winds
monsoon a seasonal wind that blows toward the
land in the summer, bringing heavy rains, and that
blows away from the land in the winter, bringing
dry weather
 Temperature differences between the land and
the oceans sometimes cause winds to shift
seasonally in some regions.
•
Monsoon climates, such as that in southern Asia,
are caused by heating and cooling of the northern
Indian peninsula.
Chapter 25
Topography
Elevation
 The surface features of the land, or
topography, also influences climate.
 The elevation, or height of landforms
above sea level, produces distinct
temperature changes.
 Temperature generally decreases as
elevation increases.
Chapter 25
Topography, continued
Rain Shadows
 When a moving air mass encounters a mountain
range, the air mass rises, cools, and loses most
of its moisture through precipitation.
 As a result, the air that flows down the other
side of the range is usually warm and dry. This
effect is called a rain shadow.
 One type of warm, dry wind that forms in this
way is a the foehn (FAYN), a dry wind that flows
down the slopes of the Alps.
Chapter 25
Climate Zone
 Earth has three major types of climate
zones: tropical, middle-latitude, and polar.
 Each zone has distinct temperature
characteristics, including a specific range of
temperatures.

Each of these zones has several types of
climates because the amount of
precipitation within each zone varies.
Chapter 25
Climates of the World
Chapter 25
Tropical Climates
tropical climate a climate characterized by
high temperatures and heavy precipitation
during at least part of the year; typical of
equatorial regions
 These climates have an average monthly
temperature of at least 18°C, even during
the coldest month of the year.
 Within the tropical zone, there are three
types of tropical climates: tropical rain
forest, tropical desert, and savanna.
Chapter 25
Tropical Climates, continued
The diagram below shows the different characteristics of tropical climates.
Chapter 25
Middle-Latitude
Climates
middle-latitude climate a climate that has a
maximum average temperature of 8°C in the
coldest month and a minimum average
temperature of 10°C in the warmest month
 There are five middle-latitude climates:
marine west coast, steppe, humid continental,
humid subtropical, and Mediterranean.
Chapter 25
Middle-Latitude Climates,
continued
The diagram below shows the different characteristics of middle-latitude
climates.
ChapterClimates
25
Polar
polar climate a climate that is characterized by
average temperature that are near or below
freezing; typical of polar regions
 There are three types of polar climates: the
subarctic climate, the tundra climate, and the
polar icecap climate.
Chapter 25
Polar Climates, continued
The diagram below shows the different characteristics of polar climates.
Chapter 25
Local Climates
microclimate the climate of a small area
 Microclimates are influenced by density of
vegetation, by elevation, and by proximity to
large bodies of water.
 For example, in a city, pavement and
buildings absorb and reradiate a lot of solar
energy, which raises the temperature of the
air above and creates a “heat island.”
 In contrast, vegetation in rural areas does not
reradiate as much energy, so temperatures in
those areas are lower.
Chapter 25
Local Climates, continued
Effects of Elevation
 As elevation increases, temperature decreases
and the climate changes.
 For example, highland climate is characterized by
large variation in temperatures and precipitation
over short distances because of changes in
elevation.
 Highland climates are commonly located in
mountainous regions—even in tropical areas.
ChapterClimates,
25
Local
continued
Effects of Large Bodies of Water
 Large bodies of waters, such as lakes,
influence local climates. The water absorbs
and releases heat slower than land does.
 Therefore, microclimates near large bodies
of water have a smaller range of
temperatures and higher annual
precipitation than other locations at the
same latitude.
Chapter 25
Studying Climate Change
climatologist a scientist who gathers data to
study and compare past and present climates
and to predict future climate change
 Climatologists use a variety of techniques to
reconstruct changes in climate.
Chapter 25
Studying Climate Change,
continued
Collecting Climate Data
 Today, scientists use thousands of weather
stations around the world to measure recent
precipitation and temperature changes.
 However, when trying to learn about factors
that influence climate change, scientists need
to study the evidence left by past climates.
Chapter 25
Studying Climate Change,
continued
Modeling Climates
 Currently, scientists use computers to create
models to study climate. The models
incorporate millions of pieces of data and help
sort the complex sets of variables that influence
climate.
 These models are called general circulation
models, or GCMs.
 Climate models predict many factors of
climate, including temperature, precipitation,
wind patterns, and sea-level changes.
Chapter 25
Potential Causes of Climate
Change
 By studying computer-generated climate
models, scientists have determined several
potential causes of climate change.
 Factors that might cause climate change
include the movement of tectonic plates,
changes in the Earth’s orbit, human activity,
and atmospheric changes.
Chapter 25
Potential Causes of Climate
Change, continued
Plate Tectonics
 The movement of continents over millions of
years caused by tectonic plate motion may
affect climate change.
 The changing position of the continents
changes wind flow and ocean currents around
the globe.
 These changes affect the temperature and
precipitation patterns of the continents and
oceans.
Chapter 25
Potential Causes of Climate
Change, continued
Orbital Changes
 Changes in the shape of Earth’s orbit,
changes in Earth’s tile, and the wobble of
Earth on its axis can lead to climate changes.
 The combination of these factors is described
by the Milankovitch theory.
 Each change of motion has a different effect
on climate.
Chapter 25
Potential Causes of Climate
Change, continued
Chapter 25
Potential
Causes of Climate
Change, continued
Human Activity
 Pollution from transportation and industry
releases carbon dioxide, CO2, into the
atmosphere.
 Increases in CO2 concentration may lead to
global warming, an increase in temperatures
around the Earth
 Because vegetation uses CO2 to make food,
deforestation also affects one of the natural
ways of removing CO2 from the atmosphere.
Chapter 25
Potential Causes of Climate
Change, continued
Volcanic Activity
 Large volcanic eruptions can influence climates
around the world.
 Sulfur and ash from eruptions can decrease
temperatures by reflecting sunlight back into
space.
 These changes last from a few weeks to several
years and depend on the strength and duration
of the eruption.
Chapter 25
Potential Impacts of Climate
Change
 Earth’s atmosphere, oceans, and land are all
connected, and each influences both local
and global climates.
 Even short-term changes in the climate may
lead to long-lasting effects that may make
the survival of life on Earth more difficult for
both humans and other species.
 Some of these potential climate changes
include global warming, sea-level changes,
and changes in precipitation.
Chapter 25 Impacts of Climate
Potential
Change, continued
Global Warming
global warming a gradual increase in the average
global temperature that is due to a higher
concentration of gases such as carbon dioxide in
the atmosphere
 Global temperatures have increased
approximately 1°C over the last 100 year.
 Researchers are trying to determine if this
increase is a natural variation or the result of
human activities, such as deforestation and
pollution.
Chapter 25
Potential Impacts of Climate
Change, continued
Global Warming, continued
 An increase in global temperature can lead
to an increase in evaporation.
 An increase in global temperatures could
also cause ice at the poles to melt.
 If a significant amount of ice melts, sea
levels around the world could rise.
Chapter 25 Impacts of Climate
Potential
Change, continued
Sea-Level Changes
 An increase of only a few degrees
worldwide could melt the polar icecaps and
raise sea level by adding water to the
oceans.
 Many coastal inhabitants would be
displaced, and freshwater and agricultural
land resources will be diminished with the
change in sea level.
Chapter 25
What Humans Can Do
 Many countries are working together to
reduce the potential effects of global
warming.
 Treaties and laws have been passed to reduce
pollution.
 Even community projects to reform areas
have been developed on a local level.
Chapter
25
What
Humans
Can Do,
continued
Individual Efforts
 Pollution is caused mostly by the burning of
fossil fuels, such as running automobiles and
using electricity.
 Therefore, humans can have a significant
effect on pollution rates by turning lights off
when they are not in use, by turning down
the heat in winter, and by reducing air
conditioner use in the summer.
Chapter 25
What Humans Can Do,
continued
Transportation Solutions
 Using public transportation and driving fuelefficient vehicles help release less CO2 into the
atmosphere.
 All vehicles burn fuel more efficiently when they
are properly tuned and the tires are properly
inflated.
 Car manufacturers have been developing cars
that are more fuel efficient. For example, hybrid
cars use both electricity and gasoline.