Air masses and fronts (weather and climate)

Global winds

trade winds, westerlies, rossby waves

synoptic scale winds

monsoon, chinook, mid-latitude cyclones

mesoscale winds

thunderstorms, land-sea breezes, mountain/valley breezes.

Microscale winds 

Turbulent eddies and dust devils 

Air mass

a distinctive body of air with specific moisture and temperature characteristics. Greater than 1000km

Air masses are characterized by

relatively horizontal homogenous temperature and moisture

Atmosphere gains water from:

evaporation off the surface 

Source regions are defined by:

surface moisture and temperature characteristics

Ideal source region must:

be extensive and physically uniform, also have a tendency to stagnate over a region

Source regions typically form 

in association with anticyclones and high pressure systems 

Classify air masses by

Surface type (continent or ocean (moisture)) and Latitude (temperature)

Continental polar (cP)

cold stable air, clear skies, high pressure, anticyclonic winds. Only in Northern Hemisphere often in winter and cold-weather.

Maritime polar (mP)

cool moist unstable air, cyclonic winds flows. Sit over oceans a high latitudes 

Maritime tropical (mT)

warm humid, stable o unstable air. Form over tropical oceans.

Lake effect snow

cause by cP or cA air moving over warm lake waters.

Fronts 

3D boundary surfaces between two air masses. Warm/moist air overruns cold/dry air. 

Frontal type is defined by:

The type of air masses, the boundary separated, and the movement of air masses.

Warm front

the leading edge of an advancing warm air mass. They gradually move up and over cold air

Warm fronts are much __ than cold fronts. 

Slower 

Precipitation falls ___ of a warm front.

Ahead

Warm air moves __ cold air

towards

Cold front 

leading edge of an advancing cold air mass. Separates warm air from cold/cool air. Steeper and faster than a warm front.  

Cold air ___ warm air up and out of the way

pushes

Precipitation falls ___ a cold front

behind

Stationary front 

separates warm air from cool/cold air. Neither air mass is advancing. 

Occluded front

when a cold front overtakes a warm front. The bigger the difference he stronger the front.

Occluded front; cold type

air behind is colder than air in front

Occluded front; warm type 

air behind is warmer that the air in front 

Dryline

Separates low humidity air from high humidity air.