WEATHER

AIR MASSAIR MASS

huge mass of air with similartemperature and humidity characteristics

name an air mass from itstemperature and humidity

huge section of the troposphere in which the temperature and humidity are fairly uniform at any given level

SOURCE REGIONSOURCE REGION

location over which an air mass sitsand acquires its

temperature and humiditycharacteristics

the humidity characteristic of an air mass comes from the type of surface of the

source region

two broad types of surfaces on earth:

waterland

land = drywater = moist

maritime continentalm c

temperature comes from latitude of the source region

equatorial E hot

tropical T warm

polar P cool or cold

arctic A very coldantarctic AA

humidity temperature

m, c E, T, P, A

mE cE

mT cT

mP cP

mA cA

8 6

NAME AN AIR MASS=one of these six choices

AIR MASS SOURCE REGIONSNorth America

mP

mT mT

mTcT

mP

cP

cP-cA

the characteristics of an air mass dominate the weather of locations within the air mass

cE--hot and dry

cT--warm and dry mT--warm and moist

cP--cool or cold and dry mP--cool or cold and moist

cA--very cold and dry

air mass weather--dominated by an air mass

air masses move away from their source regions

FRONTFRONT

boundary between two different air masses

the earth’s rotation makes a frontal boundary surface a gentle slope

warm air is less dense than cold, so the warm air rises over the colder, denser air

4 TYPES OF FRONTS4 TYPES OF FRONTS

warm front--warm air moves in to replace cold

cold front--cold air moves in to replace warm

stationary front--boundary between two different air masses which is not moving appreciably

occluded front--more complex, to be defined later

weather map symbolsweather map symbolsN

cold front

cold air

warm air

stationary front

cold air

warm air

warm front

cold air

warm air

occluded front

Cross-Section of a Warm Front

cumulonimbus

warm aircold air

Cross-Section of a Cold Front

Cross-Section of a Stationary Front

polar front begins as a stationary front

the polar northeasterlies begin to push the air mass southward, and the prevailing

southwesterlies begin to push an air mass northward

stationary front polar front

warm

cold

L

cold

warm

L

cold

L

warm

cold

warm

L

repeated illustration

for comparison

Middle Middle Latitude Latitude CycloneCyclone

Middle Latitude CycloneMiddle Latitude Cyclone polar front

cold

warm

L

warm

cold

L

cold

warm

L

cold

warm

L

OCCLUDED FRONT

cold air cool air

map view

cross-section

surfacecold-front type occlusion

cold

warm

L

cumulonimbus

cold air

Cross-Section of Middle Latitude

Cyclone with center of the low to the north

MAP VIEW

cumulonimbus

cold air

The Process of OCCLUSIONThe Process of OCCLUSION