Lecture - 7 Air Masses 2011

8/11/2019 Lecture - 7 Air Masses 2011

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Airmasses


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Learning Objectives

Identify key features of various air masses anddescribe the weather associated with each type.

Describe how air masses form and explain howair masses affect global weather patterns.

Interpret the information on a synoptic weatherchart to ascertain air masses


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Description of air masses

Air masses are either warm or cold Source region Polar or tropical .

Air masses either form at sea or land Sea Maritime Land - Continental

ITCZ - Animation
http://daphne.palomar.edu/pdeen/animations/23_weatherpat.swfhttp://daphne.palomar.edu/pdeen/animations/23_weatherpat.swfhttp://daphne.palomar.edu/pdeen/animations/23_weatherpat.swfhttp://daphne.palomar.edu/pdeen/animations/23_weatherpat.swfhttp://daphne.palomar.edu/pdeen/animations/23_weatherpat.swf


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Qu. What is an air mass?

An air mass is a large body of air withsimilar temperature and/or humidity .

Qu. Where do air masses form.They form in stable source regions such

as the sub tropics or near the poles.


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Qu. Where are the high pressure belts?


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NorthernCanada

GreenlandArctic Ocean

Siberia

TropicalOcean

TropicalOcean

TropicalOcean

Sahara

TropicalOceanTropicalOcean

TropicalOcean

Antarctica


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Source regions of Air Masses

Permanentanticyclone

Azores

Sahara Greenland Siberia

Arctic

Air mass (name)

Tropical Maritime Tropical Continental Polar Maritime Polar Continental Arctic Maritime


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Air Mass Classification

Cold & moistArctic Maritime(A or Am)

Cold & dryPolar Continental (Pc)

Cool & moistPolar Maritime (Pm)

Warm & dryTropical Continental

(Tc)

Mild & moistTropical Maritime (Tm)


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Tc Pc(winter)

Tm Pm Am rPm

Summer Winter Longsea

track

Shortsea

track

Exposed Sheltd

T Nearseatemperature

Warm

Humidity

Changeof lapserate

Littlechange

Cooledfrombelow

Heatedfrombelow

Littlechange

Cooledfrombelow

Warmedinsummer

Heatedfrombelow

Heatedfrombelow

Heatedfrombelow

Stability

Weather Brokencloud,dry

Vis


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Tropical continental (Tc)

Source region Sahara(North Africa)

Cooled from below

Stable (Un?) Dry air mass Heat wave in Summer

Usually good vis(haze? Pollution)


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Tropical Continental (Tc)

Source RegionNorth Africa / Sahara

Synoptic SituationHigh Central Europe


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Tropical Continental (Tc)Summer Winter

Temperature: Very w arm or ho t AverageHumidity: Relat ively dry Rather m ois t

Stability: General ly stab le Stable

Weather: Clear, oc casio nalthund ery show ers

Usua l ly c loudy

Visibility: Mod erate or po or Mod erate or po or

Generally British Isles during summer

Initially unstable but dry picks up moisture over Med, usually too dry

for pptn

Stable over UK

SW winds aloft can inject moisture to give Shws or TK

Vis mod or poor pollution & Saharan dust storms


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Polar Continental (Pc)

Source region Siberia Reaches UK with NE or E

winds.

High pressure North ofUK Mainly wintertime May pick up moisture

(track?) Perhaps clouds Vis varies


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Polar Continental (Pc) Winter

Source RegionEastern Europe

Synoptic SituationHigh Scandinavia

Weather


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Polar Continental (Pc)Long Sea Track Short Sea Track

Temperature: Cold Very Co ld Humidity: Moist in low est layers Very dry

Stability: Unstable Stable

Weather: Rain o r snow show ers Clea r

Visibility: Good bar show ers Moderate o r poo r

Eurasian land mass, N of 50 N & E of 25 E.Occurs in Winter Nov/Apr ( in summer land mass warms up no Hpressure cell)

H over Scan, surface winds Ely. Air v cold & dry.Longer sea track unstable, moisture added, E coast showers of rain /snowMay onward gives form of Tc air (Sea fog on East Coast)Short sea track clear skies & frost


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Tropical maritime (Tm)

Source region Azores (Caribbean)

Cooled by the sea

Stable Little or no moisture

lost

Coasts sea fog Weather south west dull, warm ocast.


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Tropical Maritime (Tm)

Source Region Azores

Synoptic SituationLow S of Iceland

Weather

Azores


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Tropical Maritime (Tm)Exposed Sheltered

Temperature: Near sea temp erature Warm Humidity: Very mo is t Mois t

Stability: Stable Stable aloft

Weather: Low c loud , d r i zzle , fog Broken c loud , d ry

Visibility: Often poor w i thcoas tal fog

Moderate

Source region: Atlantic Ocean - Azores / Bermuda

Warm sector of a depression

Warm & moist in lower layers passage over cooler waters

STABLE & close to saturation

Uplift causes low cloud & drizzle fog?


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Polar Maritime (Pm)

Most common Source region

Greenland

Warmed by the sea unstable

Showers on West

coast


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Polar Maritime (Pm)

Source RegionGreenland

Synoptic SituationLow N of Iceland

Weather


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Polar Maritime (Pm)Summer Winter

Temperature: Cool Rather co ld

Humidity: Mois t Mois tStability: Unstable Unstable

Weather: Showers in w es ternUK

Heavy s how ers ,som etimes wi th ha i land thund er main ly inexposed w es tern andhi l ly areas

Visibility: Good bar sho wers Good bar sho wers

Air starts v cold & dry

Long journey over warm Atlantic T rises rapidly

Unstable moisture content rises rapidly

Instability shws over sea & W and N British Isles

Seasonal & diurnal changes give variations


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Arctic (A)

Source region ArcticBasin

Winter/spring

Sea passage aka Am Showers of snow and

hail Scotland

Windward coastsN.Sea. Cold!


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Arctic Maritime (Am)

Source Region Arctic

Synoptic SituationLow Scan

Weather


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Arctic Maritime (Am)Summer Winter

Temperature: Cold Cold (< Pm)

Humidity: Fair ly Mois t Mois t (< Pm)Stability: Unstable Unstable

Weather: Heavy sho wers o rt h u n d e r s t o r m s

Heavy sh ow ers , som etimeswi th s now, ha il and thund erm ain ly in nor the rn Sco t l andand exp os ed co as ta l areas .

Visibility: V G o o d b a r s h w s V G o o d b a r s h w s

Blocking H to west of Ireland L S Scan

Similar to Pm shorter sea track air colder & lower humidityUnstable over UK

Oct to May hail showers or snow N Scot & down east coast.(NFD forming in this air mass widespread & heavy snow)

Uncommon in Summer heavy shwrs, TK & low T


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Returning Polar Maritime

Source region Greenland but travelssouth before turningNorth towards the UK

Cold air mass which iswarmed heading southand cooled heading north

leads to a wide variety

of weather Stratus cloud hill fog or Cb clouds and showers


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Ret Polar Maritime (rPm)

Source RegionGreenland but long seatrack

Synoptic SituationSlow moving L mid Atlantic

Weather

R P l M i i ( P )


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Ret Polar Maritime (rPm)All year

Temperature: Warm (warm er than po lar mar i t ime)

Humidity: Moist (mo is ter than polar mar i t im e)

Stability: Stable a t low levels ; u ns table alof t

Weather: Variable c loud , pos s ib le sho wers

Visibility: Main ly Good

Var of Pm

Long sea track air south over N Atlantic (unstable) then NE over UK(stable)

Slow moving L in mid Atlantic, deep trough extending S.

Stable or Unstable!!

T P T P A P


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Tc Pc Tm Pm Am rPm

Summer Winter Longseatrack

Shortseatrack

Exposed Sheltd


Warm

Humidity

Changeof lapserate

Littlechange

Cooledfrombelow

Heatedfrombelow

Littlechange

Cooledfrombelow

Warmedinsummer

Heatedfrombelow

Heatedfrombelow

Heatedfrombelow

Stability


Vis


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Tc Pc

Summer Winter Long sea

track

Short sea

trackT Very warm

Or hot Average Cold Very cold

Humidity Relatively dry Rather moist Moist inlowest layers

Very dry

Change oflapse rate

Little change Cooled frombelow

Heated frombelow

Little change

Stability Generallystable

Stable Unstable Stable

Weather Clear, ocanlTK showers

Clear Rain or snowshowers

Clear

Vis Mod or poor Mod or poor Good Mod or poor

T P A


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Tm Pm Am

Exposed Sheltered

T Near seatemperature

Warm Rather cold Cold(< Pm)

Humidity Very moist Moist Moist Fairly moist(< Pm)

Change oflapse rate

Cooled frombelow

Warmed insummer

Heated frombelow

Heated frombelow

Stability Stable Stable aloft Unstable Unstable

Weather Low cloud,drizzle

Broken cloud,dry

Variablecloud,showers

Showers(mainlycoastal)

Vis Often poor

with coastalfog

Moderate Good bar

showers

V. Good bar

showers

Pm Am rPm


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T Rather cold Cold(< Pm)

Warm (> Pm)

Humidity Moist Fairly moist(< Pm)

Fairly moist(< Pm)

Change of lapserate

Heated frombelow

Heated frombelow

Heated frombelow

Stability Unstable Unstable Unstable

Weather Variable cloud,showers

Showers(mainly coastal)


Vis Good bar

showers

V. Good bar

showers

V. Good bar

showers


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Other Air Masses?


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Other Air Masses

Eq Equatorial regionsTemp? / Humidity? / Weather?Clouds? / Pptn?.


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Other Air Masses

Eq Equatorial regionsV. warm moist and unstable

Passage over hotter land areasproduces Cu & Cb to a high level rainfall in large quantities.


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Other Air Masses - USA

Air Mass & W ?


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Air Mass & Wx?

19-21 March


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Spain: Heavy snow leads to somesignificant travel disruption.

In Burgos, more than 1,000 lorrieswere trapped in the snow.

20cm of snow fell in the Basqueregion.

On Tenerife (30N) 12 people weretrapped in their cars in Las Canadadel Teide after heavy snow fell. Switzerland

37cm of snow fell in a few hours. Austria Nearly 50cm of snow fell in someparts, cutting power to around 40,000people as power lines came down.An alysis ch art 00Z 20 March 2007

Air Mass & Wx?


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Air Mass & Wx?

Air Mass & Wx?


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Air Mass & Wx?

Air Mass & Wx in Channel?


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Air Mass & Wx in Channel?

Napoli

Wight Portland Plymouthsouthwesterly 6 or 7, increasing gale 8 to storm 10, perhaps violent

storm 11 later. Very rough becoming high. rain or showers. moderate,occasionally poor. Seas 11.5m

Air Mass & Wx?


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Air Mass & Wx?

Air Mass & Wx?


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Air Mass & Wx?


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Qu 1) Which is correct?

a) Tropical air is stable because it isheated from below.

b) Tropical air is unstable because it iscooled from below.

c) Tropical air is stable because it iscooled from below.


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Qu 2) Which air mass would move over theUK if pressure was high over Scandinavia

and there was surface winds from the East? Polar Continental


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Qu 3) Which air mass could cause advectionfog in the SW approaches to the UK in the

spring.Tropical Maritime


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Problems w / air masses?

a) No universal agreement on air massclassification

Major differences from continent to continent

b) Conditions rarely uniform in sourceregions

Ch i i f i


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Characteristics of air massesreaching the UK

A

Pc

Pm

Tc

Tm

AirCondition

SkyRHTemp.Source AirMass

Ch i i f i


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Characteristics of air massesreaching the UK

UnstableCuLow Medium

VeryLow

ArcticOcean

A

StableSt?(turb)

LowVeryLow

SiberiaPc

UnstableCuMediumLow /

High

GreenlandPm

StableClearLowVeryHigh

SaharaTc

StableCoveredwith St

HighHigh AzoresTm

AirCondition

SkyRHTemp.Source AirMass

Tc Pc Tm Pm Am rPm


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Summer Winter Longseatrack

Shortseatrack

Exposed Sheltd


Warm

Humidity

Changeof lapserate

Littlechange

Cooledfrombelow

Heatedfrombelow

Littlechange

Cooledfrombelow

Warmedinsummer

Heatedfrombelow

Heatedfrombelow

Heatedfrombelow

Stability


Vis

Tc Pc


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Tc Pc

Summer Winter Long seatrack

Short seatrack

T Very warmOr hot

Average Cold Very cold

Humidity Relatively dry Rather moist Moist inlowest layers

Very dry

Change oflapse rate

Little change Cooled frombelow

Heated frombelow

Little change

Stability Generallystable

Stable Unstable Stable

Weather Clear, ocanlTK showers

Clear Rain or snowshowers

Clear

Vis Mod or poor Mod or poor Good Mod or poor

Tm Pm Am


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Exposed Sheltered

T Near seatemperature

Warm Rather cold Cold(< Pm)

Humidity Very moist Moist Moist Fairly moist(< Pm)

Change oflapse rate

Cooled frombelow

Warmed insummer

Heated frombelow

Heated frombelow

Stability Stable Stable aloft Unstable Unstable

Weather Low cloud,drizzle

Broken cloud,dry

Variablecloud,showers

Showers(mainlycoastal)

Vis Often poorwith coastalfog

Moderate Good barshowers

V. Good barshowers

Pm Am rPm


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T Rather cold Cold(< Pm)

Warm (> Pm)

Humidity Moist Fairly moist(< Pm)

Fairly moist(< Pm)

Change of lapserate

Heated frombelow

Heated frombelow

Heated frombelow

Stability Unstable Unstable Unstable

Weather Variable cloud,showers



Vis Good bar

showers

V. Good bar

showers

V. Good bar

showers


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Learning Objectives

Identify key features of various air masses anddescribe the weather associated with each type.

Describe how air masses form and explain howair masses affect global weather patterns.

Interpret the information on a synoptic weatherchart to ascertain air masses

Tc Pc Tm Pm Am rPm


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(winter)Summer Winter Long

seatrack

Shortseatrack

Exposed Sheltd


Warm

Humidity

Changeof lapserate

Littlechange

Cooledfrombelow

Heatedfrombelow

Littlechange

Cooledfrombelow

Warmedinsummer

Heatedfrombelow

Heatedfrombelow

Heatedfrombelow

Stability


Vis

Tc Pc Tm Pm Am rPm


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(winter)Summer Winter Long

seatrack

Shortseatrack

Exposed Sheltd


Warm

Humidity

Changeof lapserate

Littlechange

Cooledfrombelow

Heatedfrombelow

Littlechange

Cooledfrombelow

Warmedinsummer

Heatedfrombelow

Heatedfrombelow

Heatedfrombelow

Stability


Vis

Lecture - 7 Air Masses 2011

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