Download Section 6.2

Water and Weather
Chapter Six: Weather and
Climate
• 6.1 Introduction to Weather
• 6.2 Weather Patterns
• 6.3 Climates and Biomes
Investigation 6B
Storms
• How does Doppler radar work?
6.2 Meteorology
• A meteorologist is a
person who uses
scientific principles to
explain, understand,
observe, or forecast
Earth’s weather.
6.2 Meteorology
• Many meteorologists
have college
degrees in physics,
chemistry, or
mathematics.
6.2 Meteorology
• Meteorologists
use satellite and
computer
technology to
inform people
about the
weather.
6.2 Water in the atmosphere
• Higher temperatures
cause liquid water
molecules to move
faster.
• These water
molecules become
water vapor in the
atmosphere.
6.2 Cloud formation
• Different conditions cause
different clouds.
• Cumuliform clouds include:
– cirrocumulus
– altocumulus
– cumulus
– cumulonimbus
6.2 Cloud formation
• Stratiform clouds form
when a large mass of
stable air gradually rises,
expands, and cools.
• Stratiform clouds include:
– cirrostratus
– altostratus
– stratus
– nimbostratus
6.2 Cloud formation
• Sometimes a cloud formation combines
aspects of both cumuliform and stratiform
clouds.
• We call these clouds stratocumulus clouds.
6.2 Cloud formation
• Cirrus clouds are thin lines of ice crystals
high in the sky, above 6,000 meters.
• They are just a thin streak of white across a
blue sky.
6.2 Rain
• Rain is the result of
a cooling air mass.
• Cooling an air mass
is like wringing out a
wet sponge.
• Tiny droplets form a
cloud or fog.
• Larger droplets fall
as rain.
6.2 Snow
• Snow usually forms
when both ice crystals
and water droplets are
present in the sky.
• The water droplets
attach to ice crystals
and freeze.
• When the ice crystals
are large enough, they
will fall to the ground as
snow.
6.2 Air masses and fronts
• An air mass is a large body
of air with consistent
temperature and moisture
characteristics throughout.
• Two air masses that affect
the United States are the
continental polar air mass
and the maritime tropical air
mass.
Changing conditions and global winds
cause these air masses to move.
6.2 Fronts
• A cold front occurs when cold air moves in and
replaces warm air.
6.2 Fronts
• A warm front occurs when warm air moves in
and replaces cold air.
6.2 Fronts
• On a weather map, a
cold front is shown
using a line marked
with triangles.
• The triangles point in
the direction the front is
moving.
• A warm front is shown
using a line marked
with semicircles.
6.2 Low- and high-pressure areas
• When a cold front moves
into a region and warm air
is forced upward, an area
of low pressure is created
near Earth’s surface at the
boundary between the two
air masses.
• A center of high pressure tends to be found where
a stable cold air mass has settled in a region.
6.2 Thunderstorms
• Thunderstorms occur
because of convection
in the atmosphere.
• The downdraft and
updraft form a type of
convection cell called a
storm cell within the
cloud.
6.2 Lightning
• Lightning is a bright
spark of light that
occurs within a storm
cloud, between a cloud
and Earth’s surface, or
between two storm
clouds.
6.2 Hurricanes
• A hurricane is a
tropical cyclone with
wind speeds of at least
74 miles (119 km) per
hour.
• The Saffir-Simpson
Hurricane Scale is one
scale used for rating
hurricanes.
6.2 Tornadoes
• A tornado, like a
hurricane, is a system of
rotating winds around a
low-pressure center.
• As the rotating wind
pattern narrows and
lengthens, it forms a
funnel cloud.
6.2 El Nino Southern Oscillations
• Storm patterns across the globe can happen in
cycles.
• Usually the trade winds blow warm water from
east to west across the Pacific Ocean.
• Every so often the trade winds weaken and the
warm water reverses direction.
6.2 El Nino Southern Oscillations
• Along with warm water comes greater
thunderstorm activity across the Pacific.
• This change in wind flow, air pressure, and
thunderstorm activity is known as the El Niño
Southern Oscillation.