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METEOROLOGY
WEATHER – SHORT TERM VARIATIONS IN ATMOSPHERIC
CONDITIONS
WHAT CAUSES WEATHER?
• The main cause of all weather is the imbalanced heating
of the Earth’s surface.
• As the various areas of Earth are heated differently, the
air interacts in various ways which we will study in this
section.
AIR MASS- LARGE VOLUME OF
AIR THAT HAS
CHARACTERISTICS OF THE AREA
OVER WHICH IT FORMS.
A (Arctic)- Extremely cold and dry, forms
over northern Canada.
cP (Continental Polar) dry and cold, forms
over central Canada.
mP (Maritime Polar) Cold and wet, forms
over northern Pacific and Atlantic oceans.
mT (Maritime Tropical) warm and wet,
forms over southern Pacific and Atlantic
Oceans.
cT (Continental Tropical) Warm and dry,
forms over Mexico in the SUMMER ONLY.
• Types of Air Masses
EXAMPLES OF AREAS
THAT HAVE SPECIFIC
AIR MASSES
cP- Central Canada, North
Dakota, Siberia
mP- Maine, Northern
Canadian Coast, Washington
and Alaska
mT- Florida, Rainforests,
Northern Australian Coast
cT- Texas, Mexico, Los Vegas,
Arizona
A- Northern Siberia, Arctic
Circle, Northern Canada and
Alaska and Greenland
cP
mP
mT
mT
cT
A
The global winds discussed in our last unit are one of
the forces that carry air masses across the globe
The Coriolis Effect causes global winds
and ocean currents to curve. This is due
to the Earth’s rotation.
**In the northern hemisphere, winds and
currents rotate clockwise.
**In the southern hemisphere, winds and
currents rotate counter-clockwise.
How come an airplane you are travelling
on never travels in a straight line?
The other force that moves these air
masses is the jet stream. It is a narrow
band of wind that occurs in the
stratosphere above large temperature
contrasts.
Jet stream
As the land and sea are heated up or
cooled down, the air above them rises
or sinks, causing a circulation.
During the day, the breeze comes from
the sea (sea breeze) because the land
heats up so quickly that the air above
it begins to rise and is replaced by air
from the ocean..
At night, the breeze comes from the
land (land breeze) because the land
cools down very quickly and air above
it sinks and moves out to sea.
Fronts- The boundary at the front of an air mass
The front created depends on the characteristics of the air
mass..
Cold Front – Cold air moves in, forcing
warm air up. Intense precipitation and
storms are common with cold fronts.
Warm Front – Warm air moves in,
displacing the cold air. The warm air rises
gradually causing widespread light precip.
Stationary Front – When 2 air masses meet
but neither advances. They are usually
similar in temperature. Causes cloudy
weather with light winds and occasional
precipitation.
Occluded Front – When a cold front catches
up to and takes over a warm front. Warm
air is forced up violently. Typically causes
strong winds and heavy precipitation.
http://www.physicalgeography.net/fundamentals/7r.html
LOW/HIGH PRESSURE SYSTEMS
Rising air (makes
clouds/precipitation)
Sinking air (no rising
air means no clouds)
ISOTHERMS AND ISOBARS
Isotherms – Lines on a weather
map of equal temperature.
Isobars – Lines on a weather map of
equal pressure.
Both can be useful in predicting and analyzing weather
WINDWARD AND LEEWARD SIDES OF A MOUNTAIN
DIRECTION OF AIR MOVEMENT OVER MOUNTAIN
WINDWARD
(WET)
LEEWARD
(DRY)
SUPERCELLS AND DOWNBURSTS
Downbursts are violent
downward drafts of wind with
speeds over 100 mph. These
winds can cause as much
damage as tornadoes.
A supercell in Montana.
Supercells are intense
rotating storms in which
updrafts can take 10-20
minutes to reach the top
of the clouds.
Cumulonimbus Clouds- these are the dangerous thunderstorm clouds,
they are also called thunderheads. These clouds usually form on a hot and
humid day when the warm air rises quickly
Lightning- is a sudden spark or discharge released from energy within a
cumulonimbus cloud. Lightning can be up to 30,000°C.
Thunder- is the sound of the explosion. Since light travels so much faster
than sound, you always see the lightning first, than HEAR there explosion
within seconds of the lightning.
Tornadoes- is a rapidly whirling, funnel-shaped cloud that reaches from
the cloud to the Earth’s surface.
Tornadoes usually last less than 15 minutes but within that time,
tornadoes can have winds speeds up to 320 miles per hour and be up to
half a mile wide!
TORNADO FORMATION
TV Warning vs WatchThunderstorm or tornado Warning means that there IS A STORM or
funnel cloud and it is heading your way!
Watch means that there is a very good chance that the thunderstorm
and tornado COULD FORM.
Tornado Safety- safest places are a strong cement basement or bath
tub with a mattress over your body. If in a car, get out! Get to a bridge
overpass or lie in a ditch with your hands over your head away from any
objects that could become projectile.
CAUSE FOR TORNADO ALLEY:
1. CP AIR MASS FROM THE NORTH MIXES WITH THE MT FROM THE SOUTH. THE LARGE TEMPERATURE
CONTRASTS CAUSE THE FORMATION OF SUPERCELLS (EXTREMELY POWERFUL THUNDERSTORMS). THE ROTATION
BEGINS WITHIN THE THUNDERSTORM CLOUDS AND THE UPDRAFTS CREATE A COLUMN WHICH INCREASES
ROTATION. THE AIR PRESSURE LOWERS IN THE CENTER CAUSES A VIOLENT INCREASE IN WIND SPEED.
The Fujita Scale Rates Tornadoes
:
F0-F1 (last 1-10 minutes and winds
up to 45-120 mph)
F2-F3 (last 20 minutes, winds up
to120-220mph)
F4- F5 (Last up to 1 hour, winds are
up to 220-340mph)
What is the most violent season
for tornadoes?
Location of Tornado Alley
Hurricane Irene
HURRICANES:
Sandy Prezi
Hurricane Formation:
1. Warm air absorbs moisture from the ocean.
2. Water Vapor is lifted into the atmosphere.
3. As the water vapor rises, the cooler upper
air condenses it into liquid droplets.
4. Condensation releases latent heat into the
atmosphere, making the air less dense.
5. As the lighter air rises, moist air from the
ocean takes its places creating a wind
current.
6. Moving air begin the rotate due the Coriolis
Effect (the process curving large wind and
water systems due to the very fast rotation
of the Earth)
7. Tropical Depression- Some thunderstorms
and winds are 25-40 mph
8. Tropical Storm- thunderstorm wall becomes
more solid, winds 42-78mph
9. Hurricane or Cyclone- distinguished eye with
a surrounding eyewall (layers of
thunderstorms that surrounds the eye) and
winds are more than 78 mph.
HURRICANE FORMATION
Hurricane Katrina
STORM SURGE
A wall of water created
as hurricane-force winds
force ocean water
toward land.