Transcript Document

AIR MASSES
A large body of air with uniform temperature and moisture characteristics.
They acquire their characteristics in source regions, because they move
slowly when passing these regions
Ex: A very cold air mass with low water vapor is generated over cold ,
snow-covered surface in artic region
AIR MASSES
• Air masses move from one region to another (pressure gradient,
upper level winds, jet stream)
•When moving, the properties are influenced by the new environment
CLASSIFICATION OF AIR MASSES
1. Latitudinal position
Air Mass
Symbol
Source region
Artic
A
Artic region
Antartic
AA
Antartica
Polar
P
Continents and
oceans (50-60°)
Tropical
T
Continents and
oceans (20-35°)
Equatorial
E
Oceans close to
equator
2. Type of surface
Maritime
Continental
m
c
oceans
continents
TYPICAL AIR MASSES
Air mass
Symbol
Source region
Properties
Maritime equatorial
mE
warm oceans in
equatorial region
warm, very moist
Maritime Tropical
mT
warm oceans in tropical
region
Warm, moist
Continental tropical
cT
Subtropical deserts
Warm, dry
Maritime polar
mP
Midlatitude oceans
Cool, moist(winter)
Continental polar
cP
Northern continental
interiors
Cold, dry (winter)
Continental artic
cA
Regions near north pole
Very cold and dry
Continental antartic
cAA
Regions near south pole
Very cold and dry
TYPICAL AIR MASSES
See Figure 6.2 Page 155
NORTH AMERICAN AIR MASSES
Strong influence on North American weather
1.
Continental Polar (cP)
Tongues of cold dry air; periodically extend
S,E producing cold temperatures and clear
skies
2. Continental Artic (cA)
When moving southward: severe cold wave
3. Maritime Polar (mP)
Unstable in winter: heavy precipitation over
coastal ranges
4. Maritime Tropical (mT)
Moves northward bringing moist unstable air:
thunderstorms
See Fig 6.3, page 156
5. Continental Tropical (cT)
Does not move widely, influence
weather conditions over source region
FRONTS
Transition zone between two air masses of different characteristics
COLD FRONT
Transition zone where a cold air
mass invades a warmer air mass
Colder air mass remains in contact
with ground (because is denser)
It forces warm air mass to rise
If warm air is unstable:
thunderstorms
PRECIPITATION IN A COLD FRONT (ANIMATION)
FRONTS
WARM FRONT
Transition zone where a warm air
moves into a region of colder air
Cold air remains in contact with
ground (denser)
It forces warm air mass to rise
If warm air is stable:
Steady precipitation
If warm air is unstable:
thunderstorms
PRECIPITATION IN A WARM FRONT (ANIMATION)
OCCLUDED FRONT
When a cold front overtakes a warm front (cold fronts move at a
faster rate than warm fronts)
STATIONARY FRONT
A front that is not moving. Masses are not strong enough to
replace each other
There is a noticeable temperature change and shift in wind direction between
two sides of front
THE PRESIDENT SNOW STORM (Feb 16-17 2003)
Stationary front
WEATHER
The condition of atmosphere at any particular time
and place. It’s always changing
CLIMATE
Weather surface map, July 02 2008
The synthesis of weather, the average weather of
a region over a period of time
Annual average precipitation
WEATHER SYSTEMS
Some patterns of wind circulation present recurring patterns of weather
Weather systems:
Few kilometers (tornado)
Thousands kilometers (a large traveling cyclone)
CYCLONES
Air spirals inward and upward
condensation, precipitation
ANTICYCLONES
Air spirals outward and downward
condensation cannot occur
TRAVELING CYCLONES AND ANTICYCLONES
CYCLONES AND ANTICYCLONES: masses of air moving in
a spiraling motion
Most of them are large features moving slowly across Earth’s
surface and bringing changes to weather.
TRAVELLING CYCLONES AND ANTICYCLONES
TYPES OF CYCLONES:
1.
2.
3.
Wave cyclones (middle and high latitudes, ~1000km or 600miles)
Tropical cyclones (hurricanes, typhoons)
Tornado
WAVE CYCLONES
The wave cyclone forms, intensify and dissolves along the polar front
Conditions to form: two anticyclones, one with warm air, and the other
with cold polar air are in contact in the polar front.
WAVE CYCLONE FORMATION
See Fig 6.8 page 161, 162
A. Early stage:
There is a wave formation in the polar front
Cold air is going southward and warm air
is moving northward
B. Open stage:
Wave is deepened and intensified
C. Occluded stage:
Cold front overtakes warm front
(occluded front)
Precipitation is intensified
D. Dissolving stage:
The cold front is reestablished
HOW DOES A WAVE CYCLONE AFFECT WEATHER?
See page 162
MARCH 21, 22 2005
http://www.hpc.ncep.noaa.gov/dailywxmap/index.html
JUNE 12, 2004
JUNE 27 2008
JUNE 28 2008
JUNE 29 2008