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

2. Type of surface

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

Maritime m oceansContinental c 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

See Fig 6.3, page 156

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

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 riseIf 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 riseIf warm air is stable:Steady precipitationIf 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

CLIMATE

The condition of atmosphere at any particular time and place. It’s always changing

The synthesis of weather, the average weather of a region over a period of time

Weather surface map, July 02 2008

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 ANTICYCLONES

Air spirals inward and upward

condensation, precipitation

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. Wave cyclones (middle and high latitudes, ~1000km or 600miles)

2. Tropical cyclones (hurricanes, typhoons)3. 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

frontCold 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