Download Maritime equatorial (mE)

4/24/2012
Air Masses
Classified by latitude and source regions
• Maritime
equatorial (mE)
tropical (mT)
• Continental tropical (cT)
• Maritime polar (mP)
• Continental Arctic (cA)
• Continental Antarctic (cAA)
• Maritime
Weather Systems
Geo210
Moisture
An Introduction to Physical Geography
Continental (c) Air Mass – dry
Maritime (m) Air Mass - moist
Michael Paluzzi, ABD
Weather
Weather – short-term, day-to-day expression of
atmospheric processes
Ex. - Today is clear, cold and sunny
Climate – long-term, average conditions
Usually at least 30 years of daily weather data
(temperatures and precipitation)
Ex. - CT – Humid Continental, warm summer
Climate regions – boundaries drawn around areas
with similar average climate conditions
Meteorology – the scientific study of the atmosphere
Air Masses
Air mass – homogeneous body of air that has
taken on the moisture and temperature
characteristics of it’s source region
Earth’s surface get it’s temperature and
moisture characteristics from these air masses.
Regional air masses has differing
temperature, humidity and stability
Air Mass Types
Continental Polar (cP)
Occur only in northern hemisphere
Responsible for weather in mid and high
latitude locations
Cold dense air lifts warm moist air

Producing lifting, cooling, condensation
Greater difference in cold and warm air masses,
more dramatic weather produced
Lack of landmasses in southern hemisphere prevent
the occurrence
Lake-Effect Snow
cP air masses move south and east
Cold air passes over warmer Great Lakes
Air masses are warmed and water vapor added
As the air masses move over cold land, they cool
and reach the dew point, where the condensation
falls as heavy snow
Their interaction produces weather patterns
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Lake-Effect Snow
Atmospheric Lifting Mechanisms
Convectional Lifting
FL – landmass warmer than Gulf of Mexico
Local heating lifts warm, moist
from the Gulf of Mexico, as it
passes over the warmer land
Causing frequent afternoon
showers
Atmospheric Lifting Mechanisms
Atmospheric Lifting Mechanisms
Convergent Lifting - air along the surface
flows toward a low pressure center and rises
Orographic Lifting - air is forced over a
barrier (like a mountain range)
Common in the tropics
NE & SE trade winds
converge
Forming large
cumulonimbus clouds
High average annual
temperatures
Windward side – wet
Leeward side – dry
Rain Shadow
Atmospheric Lifting Mechanisms
Convectional Lifting - stimulated by local
surface heating
Maritime air mass passes over continental
Heating from land causes lifting
Atmospheric Lifting Mechanisms
Orographic rainfall
it occurs in the Western Ghats and Himalayas in South
Asia – resulting in
Rain-shadow effect: the area of low rainfall found on
the leeward (or downwind side) of a mountain range
Plowed fields

Local heating due to dark soil
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Atmospheric Lifting Mechanisms
Cold Fronts
Orographic rainfall
Atmospheric Lifting Mechanisms
Frontal Lifting (Cold and Warm Fronts) along the leading edges of contrasting air
masses.
Front – a place of atmospheric
discontinuity, a narrow zone forming a line
of conflict between two air masses
Cold Front – Squall Line
Squall line – fast moving cold front that forms a
line of severe storms along a cold front
Large cumulonimbus clouds form, producing heavy
precipitation, hail, frequent lightning, strong straight
line winds, and possibly tornadoes
Leading edge of cold air
mass is a cold front
Leading edge of warm air
mass is a warm front
Frontal Lifting - Cold Front
Cold Fronts
Denser, advancing cold air forces warm, moist air to lift
abruptly. As the air is lifted, it cools by expansion,
cooling to the dew - point as it rises it condenses and
forms clouds.
Cumulonimbus clouds may produce large raindrops,
heavy showers, lightning and thunder, and hail.
Frontal Lifting – Warm Front
Warm front: moving weather front along which a
warm air mass slides over a cold air mass
Gentle lifting of the warm, moist air produces
nimbostratus and stratus clouds and drizzly rain
showers – sometimes a thunderstorm
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Warm Fronts
Dangerous Weather
Sleet – frozen raindrops or partially refrozen
snowflakes that bounce when they reach the
ground
Stationary Front
Stationary Front: two air masses are in
contact, but there is little or no relative
motion
Once this boundary resumes its forward
motion, it once again becomes a warm front or
cold front
Rain
Dangerous Weather
Freezing Rain – precipitation that
starts as snow at high altitudes,
melts and freezes after it hits the
ground
Violent Weather
Thunderstorms - condensation of large amounts of
water vapor creates lots of energy, heating the air Causes up drafts
Raindrops form and cause
friction as they fall, causing
downdrafts
Giant cumulonimbus clouds
cause dramatic weather
Heavy rain, lightning,
thunder, hail, heavy winds
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Violent Weather
three months' NASA's Lightning Imaging Sensor (LIS)
records all lightning strikes between 35° N and 35° S latitudes
Hailstones
Hail is a form of precipitation which
consists of balls or irregular lumps of ice
Form in strong thunderstorm clouds,
particularly those with intense updrafts
Water droplets accumulate as ice falls, updrafts
carry it up, then falls again – creating another
layer of ice.
Once it’s too heavy for updraft, it falls to
ground
Stronger the updrafts – larger the hail stones
Violent Weather
Hailstones
Thunder – produced by a sonic shock wave
caused by the rapid expansion of the air
surrounding a bolt of lightning.
can range from a sharp, loud crack to a long,
low rumble
Figure 8.21
Violent Weather
Lightning – flashes of light caused by
atmospheric discharge of electricity
Freak Hailstorm, Bogota, Colombia,
November 3, 2007
These discharges heat the air to temperatures
15000 ° C – 30000° C
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Violent Weather
Derecho – straight line wind associated with
a thunderstorm
winds associated with derechos blow straight
ahead – not in circles like tornadoes
Violent Weather
Birth of a Tornado
Mesocyclone forms as a
rotating updraft within the
thunderstorm.
mesocyclone: a rapidly
rotating air mass with a
thunderstorm that often
gives rise to a tornado
If one forms, a tornado will
descend from the lower
portion of the mesocyclone.
Violent Weather
Tornadoes
Birth of a Tornado
Air at higher altitudes moves faster than surface
air
Creating rotation in the air parallel to the ground
Violent Weather
Violent Weather
Birth of a Tornado
Updrafts create a shift in
the axis of rotation
rotation in the air
perpendicular to the
ground
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Violent Weather
Fujita Scale – scale for rating tornado intensity based on
damage to human-made structures, vegetation
Category
Wind Speed
F0
65-85 mph
F1
86-110 mph
36%
Moderate Damage: severe roof damage, mobile homes
overturned, broken glass
F2
111-135 mph
19%
Considerable Damage: roofs torn off, foundations
shifted, large trees snapped, cars lifted off ground
F3
136 -165 mph
Severe Damage: severe damages to large buildings
(malls), trains overturned, structures with weak
foundations blown great distances
F4
166-200 mph
1%
Devastating Damage: homes completely leveled, cars
thrown, small missiles generated
F5
>200 mph
<0.1%
Incredible Damage: houses swept away, cars carried
100 meters, structural damage to high-rises
39%
5%
Potential Damage
Light Damage: Minor roof damage, gutters, siding
damaged
Branches broken off trees
Top Ten Deadliest Tornadoes
Rank
1
States
Date
MO-IL-IN March 18, 1925
F-Scale
F5
Dead
Injured
695
2027
Murphysboro, DeSoto
LA-MS
May 7, 1840
317
109
Nachez
3
MO-IL
May 27, 1896
255
1000
St. Louis, E. St. Louis
4
MS
April 5, 1936
216
700
Tupelo
5
GA
April 6, 1936
203
1600
Gainesville
181
970
Glazier, Higgins
TX-OK-KS April 9, 1947
F5
F5
7
LA-MS
April 24, 1908
8
WI
June 12, 1899
9
MI
June 8, 1953
F5
115
844
Flint
10
TX
May 11, 1953
F5
114
597
Waco
F5
Figure 8.23
Tornadoes
Towns
2
6
Tornado Damage
143
770
Amite,. Pine, Purvis
117
200
New Richmond
Figure 8.25
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F5 Tornado, Oklahoma City, May 3, 1999
Saffir-Simpson Hurricane Scale
1995 Atlantic Storm Season
Tropical Cyclones
Tropical cyclone: generic term for low pressure
system over tropical waters
with convection – thunderstorms
rotation – cyclonic circulation.
Air masses originate in tropics (doldrums – 10°)
Fueled by warm moist air of the tropics
Figure FS 8.1.1
Hurricane Andrew
Tropical Cyclones
Tropical Depression: maximum sustained winds of 39 mph
Tropical Storm: maximum sustained winds of 74 mph
Hurricane: minimum sustained winds of 75 mph
(Northeast Pacific, North Atlantic, South Pacific Ocean)
Typhoon: Northwest Pacific Ocean
Severe Tropical Cyclone: Southwest Pacific Ocean,
Southeast Indian Ocean
Severe Cyclonic Storm: North Indian Ocean
Tropical cyclone: Southwest Indian Ocean
Figure 8.31
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