Download Mon Nov 25- Review of AM,HL, Fronts Brittany O

SCIENCE 10: WEATHER
Air masses, high and low pressure
sysems, warm and cold fronts
Air is usually in motion
(Convection and the Coriolis effect)
BUT
Large portions of air
often remain in nearly the same place
long enough to take on the
temperature and moisture characteristics
of the land or ocean below
• Air masses can interact as they move and
even collide, and when they do….
• We get weather!
• The zone b/w interacting air masses is
called a front
• Eventually moves due to worldwide wind
currents
Cold Fronts
• We said rain often occurs with cold
fronts…why?
• Warm air is pushed up by cold air and
condenses
• If the cold front is fast moving
intense thunderstorms may develop
sometimes bringing hail and
tornadoes
Cold Fronts
Warm Front
• Warm air mass overtakes a cooler one
• Warm air gently rides up over the trailing
end of the cold air mass
• Precipitation may last longer than with a
cold front
• Once it passes, the air is left warmer than
before the front arrived
Warm Fronts
Stationary Fronts
• Two air masses (warm/cold) in contact
but neither is moving
• Some warm air rises and condenses
creating stratus clouds and often rain
• The front may remain this way for several
days
• = dreary, gloomy sky
Occluded Fronts
• A faster moving cold front catches up to a
slower moving warm front
• All the warm air is pushed up, away from
the ground, contacting the leading cold air
mass
• Many types of clouds are present, one
after another
• Often cause a period of steady
precipitation
High Pressure Systems
• Air descends into a region, which puts
more pressure on that region.
• An air mass cooled by conduction and
convection when it forms over cold
ground becomes more dense and settles
lower to the ground
• Creates more pressure, continues to settle,
draws more air from above
High Pressure Systems
• Air is also pushed out toward low pressure
areas at the perimeter in all directions
• This air curves to the right due to the
Coriolis Effect
• High pressure systems create a clear sky
(since air is descending not rising)
• May be 100’s of kms across
Low Pressure Systems
1. Very intense heating of the ground heats
air above it (conduction)
Air rises, pulling more, less dense air in
beneath it
Air curves to the right (Coriolis Effect) so
rising air rotates
Low Pressure Systems
2. Warm air rises in a frontal system creating
low pressure systems
Generally smaller than high pressure
systems
Likely to occur b/w air masses
Bring unstable weather conditions (cause
precipitation and often storms)
• Why do we get nice weather with high
pressure systems and storms and rain happen
with low pressure systems?
Wind
• Let’s hear it from Bill
• If time, let’s review weather office website to
see what the high and low pressure systems
can look like!
Next Class: Storms!
• Let’s ask Bill Nye!