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Air Masses and Fronts: Characteristics, Classification, and Impacts, Slides of Environmental Science

An in-depth exploration of air masses and fronts, their formation, classification, and impacts on weather patterns. topics such as the properties of air masses, source regions, fronts on weather maps, and their association with high and low-pressure systems. The document also discusses the differences between cold and warm fronts, stationary fronts, and occlusions.

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2021/2022

Uploaded on 09/12/2022

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Chapter 9 : Air MassChapter 9 : Air Mass
Air Masses
Fronts
ESS124ESS124
Prof. JinProf. Jin--Yi YuYi Yu
Fronts
Fronts on Weather Maps
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Download Air Masses and Fronts: Characteristics, Classification, and Impacts and more Slides Environmental Science in PDF only on Docsity!

Chapter 9 : Air MassChapter 9 : Air Mass •^ Air Masses •^ Fronts

ESS124ESS124Prof. JinProf. Jin-

Fronts

•^

Fronts on Weather Maps

Air masses^ Contain uniform temperature andContain

uniform temperature and

humidity characteristics.

Fronts^ Boundaries between unlike airBoundaries

between unlike air

masses.

ESS124ESS124Prof. JinProf. Jin-

Source RegionsSource Regions

•^

The areas of the globe where air masses from arecalled source regions.

•^

A source region must have certain temperatureand humidity properties that can remain fixed for asubstantial length of time to affect air massesabove it.

•^

Air mass source regions occur only in the high orlow latitudes; middle latitudes are too variable.

ESS124ESS124Prof. JinProf. Jin-

Cold Air MassesCold Air Masses

January

July

-^

The centers of cold air masses are associated with high pressure on surface weather maps.

-^

In summer, when the oceans are cooler than the landmasses, large high-pressurecenters appear over North Atlantic (

Bermuda high

) and Pacific (

Pacific high

). ESS124ESS124Prof. JinProf. Jin-

-Yi YuYi Yu

-^

In winter, high-pressure centers form over the northern parts of Asian continent( Siberian high

)^ and North America.

Classification of Air MassesClassification of Air Masses

-^

Air masses are classified according to the temperature

d^

i t

h^

t^

i ti

f th i

i

and moisture characteristics of their source regions.

-^

Bases on moisture content: continental (dry) andmaritime (moist)

-^

Based on temperature: tropical (warm), polar (cold),

p^

p^

(^

), p

(^

arctic (extremely cold).

-^

Naming convention for air masses: A small letter (

c

-^

Naming convention for air masses: A small letter (

c ,

m

) indicates the moist content followed by a capital

letter (

T

,^

P

,^ A

) to represent temperature.

ESS124ESS124Prof. JinProf. Jin-

Five Types of Air MassesFive Types of Air Masses

ypyp

-^

Theoretically, there should be 6types of air masses (2 moisturetypes of air masses (2 moisturetypes x 3 temperature types).

-^

But mA-type (maritime Arctic)But mA type (maritime Arctic)does not exist.

-^

cA: continental Arctic cP: continental PolarcT: continental TropicalcT: continental TropicalmP: maritime Polar

ESS124ESS124Prof. JinProf. Jin-

mT: maritime Tropical

Modification ofModification of cP

cP Air Masses

Air Masses

-^

Migrations of cP air inducecolder drier conditions overcolder, drier conditions overaffected areas.A

P

i^

i^

t^

t^

d l

-^

As cP air migrates toward lowerlatitudes, it warms from beneath.

-^

As it warms, moisture capacityincreases while stabilitydecreasesdecreases.

ESS124ESS124Prof. JinProf. Jin-

Continental Arctic (Continental Arctic (cA

cA) Air Masses

) Air Masses

•^

Continental Arctic (cA)

air represents extremely cold and dry

conditions as, due to its temperature, it contains very little watervapor.

-^

The boundary between cA and cP air is the shallow (~1-2 km)arctic front.

ESS124ESS124Prof. JinProf. Jin-

•^

cA air masses can extend as far southward as the Canadian-United State.

Maritime Polar (Maritime Polar (mP

mP) Air Masses

) Air Masses

-^

Maritime polar air masses form overupper latitude oceanic regions and arepp

g

cool and moist.

-^

mP air masses form over high-latitudeocean as cP air masses move out from the interior of continents. (i.e., cP

Æ

mP).

-^

Oceans add heat and moisture into the dryand cold cP air masses.

-^

Along the west coast of the U.S., mP airaffects regions during winter and may bepresent before mid-latitude cyclonesd

t^

th

ti^

t

advect over the continent.

-^

Along the east coast, mP air typicallyaffects regions after cyclone passage asthe mP air wraps around the area of low

ESS124ESS124Prof. JinProf. Jin-

the

mP air wraps around the area of low pressure.

Maritime Tropical (Maritime Tropical (mT

mT) Air Masses

) Air Masses

p

(

p

(

))

•^

Form over low latitude oceans and assuch are very warm humid andsuch are very warm, humid, andunstable.

-^

mT air masses from Atlantic and Gulff M

i^

i^

h^

i

of Mexico is the primary sourceregion for the eastern U.S.

-^

As air advects over the warm continent in summer the highhumidity and high heat occasionallycombine to dangerous levels.

-^

mT air masses have an enormousinfluence on the southwestern U.S,particularly in summer.

Advection of mT air also

ESS124ESS124Prof. JinProf. Jin-

p^

y

Advection

of mT air also

promotes the so-called Arizonamonsoon.

Cold FrontsCold Fronts

-^

Cold fronts form when cold airdisplaces warm air.

p

-^

Indicative of heavy precipitationevents, rainfall or snow, combined with rapid temperature drops.

-^

Steep front slope, typically 1:100.

-^

Moving faster, up to 50 km/hr (30mph).

-^

Northwesterly winds behind a coldfront, and southwesterly in ahead of

ESS124ESS124Prof. JinProf. Jin-

the front.

Cold Front WeatherCold Front Weather

  • The type of precipitation that will occur

along a cold front depends on thecharacteristics of the warm air ahead ofcharacteristics of the warm air ahead ofthe front.

  • If the warm air is moist and

diti

ll^

t bl

th

d^

t

conditionally unstable, thunderstormscan be triggered ahead of the coldfront; the thunderstorms will form in ali^

ll d

ll li

if^

ll

line called squall line; if supercellthunderstorms form, tornadoes, hail,damaging wind can occur.

  • If the warm air is stable, the clouds that

form by lifting only produce light rain.

  • If the warm air is dry and stable no

ESS124ESS124Prof. JinProf. Jin-

-Yi YuYi Yu

If

the warm air is dry and stable, no clouds will form at all.

Warm FrontsWarm Fronts

-^

Created when warm air displaces colder air.

-^

Shallow horizontal stratus clouds and light precipitation.

-^

Frontal fogs may occur as falling raindrops evaporate inthe colder air near the surface. Sleet and freezing rain mayalso formed.

ESS124ESS124Prof. JinProf. Jin-

-^

Half the slope of cold fronts, typically (1:200).

-^

Moving slower, about 20 km/hr (12 mph).

Warm Front WeatherWarm Front Weather

  • Clouds are deepest just north of the

warm front boundary and progressivelybecomes thinner and higher toward the north.

  • The intensity of the precipitation

depends on the stability of the warmdepends on the stability of the warmair.

  • If the warm air is conditionally

t bl

th

d^

t^

d^

l

unstable, thunderstorms may developover the warm front.

  • If the warm air is stable, the clouds will

be layered.

  • If the temperature in the cold air is

below freezing snow ice pellets or

ESS124ESS124Prof. JinProf. Jin-

-Yi YuYi Yu

below

freezing, snow, ice pellets, or

freezing rain may occur.