Transcript Chapter 3 - TeacherWeb

• An air mass is a large volume of air in which
temperature and humidity are nearly the same in
different locations at the same altitude
• Forms when air over a large region of Earth sits in one
place for many days. Takes on the characteristics of the
land below it.
•
•
•
•
Depend on the region where it
forms. Ex.- a hot desert-a dry hot
air mass; cool ocean water-moist,
cool air mass
Each category name is made of
two words- one for moisture and
one for temperature.
The 1st word tells if it was formed
over water or dry land. It describes
the moisture:
Continental-forms over land
Maritime-forms over water
The 2nd word tells if it was formed
close to the equator. It describes
temp.
Tropical- forms near equator
Polar-forms far from equator
• Air masses can travel
away from the region
where they form
• When they travel they
bring the
characteristics with it
• Air mass can change
slowly or quickly
depending on speed
of global winds
• A front is a boundary between air masses
• Different types of fronts produce different patterns of
weather
• The term “front” was first used by scientists during WW1
when compared to clashing air masses similar to armies
chasing on the battlefield
• Forms when a cold air mass pushes a warm air mass
and forces the warm air to rise.
• As the warm air rises, its moisture condenses and forms
clouds. Brief, heavy storms.
• Triangles show the direction that a cold front moves.
• A warm front moves more slowly than a cold front.
• The warm air rises slowly over the cold air and its
moisture condenses into flat clouds.
• Semicircles show the direction that a warm front moves.
• A stationary front occurs when two air masses push
against each other without moving.
• A stationary front becomes warm or cold when one air
mass advances.
• Alternating triangles and semicircles show a stationary
front.
• Formed when air
moves all the way
around a high
pressure center
• Most are large and
change slowly
• Generally bring clear
skies and calm
air/gentle breezes
• A large weather system that
surrounds a center of low
pressure.
• Begins as air moves around
and inward toward the
lowest pressure and then
up to higher altitudes
• Can happen along
boundaries of warm and
cold air
• Air spirals around and
moves in counter clockwise
direction
• Stormy weather
• Near the equator, warm ocean
water provides the energy that
can turn a low pressure center
into a violent storm
• Tropical storm: low pressure
systems that starts at equator
and has winds that blow at 40
miles per hour
• Hurricane: tropical low
pressure system with wind
speeds of 74 miles per hour or
greater
• Hurricanes that form over the
Indian Ocean or western
Pacific Ocean are called
typhoons or cyclones
• Need energy from
warm water (80
degrees F)
• Can move in many
directions but usually
westward with trade
winds
• As hurricane moves
over land or cooler
water it loses energy
• Center of hurricane is
a small area of clear
calm air- called the
eye.
• Can produce huge
waves, strong winds
and heavy rains
• Tornadoes can be
generated
• When a hurricane
moves into a coastal
area, it often pushes
a huge mass of ocean
water known as a
storm surge
• Blizzards: heavy , deep
snow with 35 miles/hour
winds and very low
temperatures
• Lake-effect snow
storms: just east and
south of the Great Lakes,
moisture released as
snow
• Ice storms: rain falls to
ground then freezes,
slippery roads
• Warm humid air near
the ground moves
into cooler air above
and rises quickly
• A thunderstorm is a
storm with lightening
and thunder
• Thunder is the effect
of lightning
1. Rising humid air forms a
cumulus cloud. The water
vapor releases energy
when it condenses into
cloud droplets. This
energy increases the air
motion. The cloud
continues to build into tall
cumulonimbus clouds of
a thunderstorm.
2. Ice particles form in the
low temperatures near
the top of the cloud. As
the ice particles grow
large, they begin to fall
and pull cold air down
with them. This strong
downward draft brings
heavy rain or hail-most
severe stage of a
thunderstorm.
3. The downward draft
can spread out and
block more warm air
from moving upward
into the cloud. The
storm slows down
and ends.
Flash Floods: can cause
overflow of rivers,
streams, lakes
Winds: over 170 miles/hour
Hail: can kill crops and
livestock in minutes,
damage livestock
Lightening: can kill or
cause serious human
injury, damage power
lines, spark forest fires
• Tornado- Violently rotating
column of air stretching from a
cloud to the ground
• Tornadoes become visible
when water droplets appear in
the center of the rotating
column. May lift dust and
debris from the ground-bottom
becomes visible
• A spinning column of air is not
called a tornado unless it
touches the ground. If it
touches H2O instead, it is
called a water spout.
• They can lift or completely demolish sturdy building
• Moves along same path with a thunderstorm
• A tornado watch is issued when conditions might
produce a tornado. A warning issued when a tornado
has been detected
• Meteorologists: scientists who studies weather
• Radar station: locates clouds and their heights, Doppler can detect
air motion and precipitation
• Satellites: images can show cloud cover, warm and cool air regions
and invisible water vapor
• Airplanes and ships: carries instruments that can take
measurements
• Ground stations: measure air pressure, temperature, dew point,
precipitation, wind speed, wind direction and cloud cover
• Weather balloons: measure air at different altitudes, can go into
stratosphere
• Weather buoys: measure conditions in ocean that can affect
atmosphere
• The use of symbols and colors can show fronts,
systems and precipitation
• An isobar is a line that
connects places that
have the same air
pressure
• Each isobar is labeled
with the air pressure in
units called millibars.
• Lines close together
show a big difference in
air pressure and strong
winds are expected
• Lines far apart where the
air pressure is almost
even and expect calm or
light breezes
• This visible light
satellite image shows
clouds from above.
The patches of white
are clouds.
• This infrared image also shows clouds but uses colors to
show temperature and high or low clouds.
• Meteorologists might
observe clouds or
weather conditions to
infer that a front is
approaching or use
observations that
have been collected
and displayed on
maps.