Section 5 TB super slides meteorology

7/28/2019 Section 5 TB super slides meteorology

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CAE NLS sect5 TB 1

5. Airmasses and fronts


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CAE NLS sect5 TB 2

Air mass and source region

Definition : An air mass is a large body of air whose physical properties, especially temperature and vertical lapse rate,moisture content and vertical distribution of moisture are moreor less uniform horizontally.

Horizontal dimensions of an air mass are in the order of

1000 km, vertical dimensions in the order of at least 1 km.


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CAE NLS sect5 TB 3

Air masses are formed over so-called source regions .

Extensive* surface of uniform temperature andhumidity:

i.e. oceans, deserts, snow covered areas.

If air stays for several days over an uniform area, itstemperature becomes the temperature of that area. Theair also takes the moisture properties of the source area.

High pressure areas are often permenant* for a longer period and therefore most favorite to form airmasses.


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CAE NLS sect5 TB 5

Geographical classification of air masses

0

30

30

45

45

70

70

A

A

A = arctic air

P

P

P = polar air

T

T

T = tropical air

E

E

E = equatorial air


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CAE NLS sect5 TB 6

Geographical classification Continental or maritime

if the source region is land the air mass will become

less moist/drier continental air

if the source region is water the air mass will become

more moist/humid maritime airi.e.: continental polar air = cP (dry Polar air)

maritime polar air = mP (moist Polar air)

This classification is important for the humidity but also for thetemperature. A continental air mass has greater extremetemperatures in winter and summer than a maritime air mass.


7/81CAE NLS sect5 TB 7

Air masses

1) Arctic air 2) Polar air 3) Tropical air 4) Equatorial air

Can be continental or m aritime

So we have 8 airmasses:

cA mA, cP mP, cT mT, cE mE


8/81CAE NLS sect5 TB 8

Air mass modification is called transformation

air mass that leaves its source region will change intemperature

and humidity thermodynamic changes: (warming/ cooling)

dynamic changes (wind/turbulent mixing)

moisture changes: (evaporation/ condensation)

i.e.: mT-air cP-air (after a long period)


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CAE NLS sect5 TB 10

Thermodynamic classification of air masses

Definition:

An air mass has warm mass properties when thetemperature at 1.5 m height is higher than the temperatureof the underlying earth's surface.

An air mass has cold mass properties when the temperatureat 1.5 m height is lower than the temperature of theunderlying earth's surface.


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CAE NLS sect5 TB 11

Warm and cold mass properties

Stability??? Stable Unstable


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CAE NLS sect5 TB 12

WEATHER PHENOMENON

COLD MASSPROPERTIES

WARM MASSPROPERTIES

stability

unstable stable

convection

yes no

low clouds

- dry air: 0/8-2/8 Cu- moist air: 4/8-7/8 Cu/Cb

- dry air: 0/8-18 St/Sc- moist air: 7/8-8/8 St/Sc

precipitation

showeryrisk of TSrisk of hail

steadylight (to mod) RA/DZno TS, no hail

visibility

good/very goodexcept in showers

moderate/poor

weather

breaks and showers fog, mist, haze, RA/DZ

turbulence

turbulent, gusty windssevere turbulence possible

laminar windmainly light turbulence at SFC

surface wind

direction: gustyspeed: variable with gusts

direction: steadyspeed: steady

angle between surface windand wind above frictionlayer

Small ca 10-30 gr Large up to 70 gr

veering of wind withincreasing height (NH)

little veering wind veers strongly

windspeed in the frictionlayer

slow increase with height rapid increase with height atinversion heigt


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CAE NLS sect5 TB 13

Diurnal variability and differences sea-land

daytime/cold * mass/unstable nighttime/warm mass/stable

cold sea/warm mass/stable warm land/cold mass/unstable

warm sea/cold mass/unstable cold land/warm mass/stable


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CAE NLS sect5 TB 14

Equatorial air can not reach w-europe


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CAE NLS sect5 TB 15

LOKALE CLASSIFICATIE

s zomers kms winters wm

mPL

mPL

mTL

cTLcTL

cPL

cAL

cALmAL

voorn. in winter en vroege

voorjaar

s zomers wms winters km

altijd km m e

e s t a l k m

s z o

m e r s

s o m s w m

altijd wm

meestal km

meestal wms zomers

soms km

s zomers wms winters km

cTL


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CAE NLS sect5 TB 16

Air masses(and fronts)


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CAE NLS sect5 TB 17

ZWARE VLOEISTOF of LUCHT DRINGT ONDER LICHTERE:Het grensvlak is het frontvlak

WATER

OLIE

Potentile energie gaat over in kinetische

energie, beweging van de lucht: WINDDe wind verplaatst de fronten.

Koude lucht dringt onder warme lucht!


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CAE NLS sect5 TB 18

De Aarde (NH)

Warm

Koud

De basis van alles* !! De koud-warm verdeling zorgtvoor fronten.

Fronten gaan golven*! Er ontstaan depressies en die zorgenvoor Wind .

Zo ontstaat de verdeling van Hoge en Lage drukgebieden!

L

Front


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CAE NLS sect5 TB 19

FRONTS

Definitions:

The frontal surface is the boundary between 2 air masses. (100 to 2000 m thick)

A front is the intersection line of a frontal surface withthe earth.

The frontal slope ( ) is the angle between the frontalsurface and the earth.


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CAE NLS sect5 TB 20

When the warmer air moves towards the colder air, whenthe warmer* mass is replacing the colder, the front iscalled a warm front . (WF)

Frontal slope 1:100-200


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CAE NLS sect5 TB 21

Embedded CB

Movement of front

ColdWarm FZL


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CAE NLS sect5 TB 22

When the colder air moves towards the warmer air, whenthe colder air is gaining ground, the front is named a cold

front . (CF)

Frontal slope: 1:50-100


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CAE NLS sect5 TB 23

Embedded CB

Movement of front

Cold Warm

Makkelijker bij KF


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CAE NLS sect5 TB 24

Frontal wave

1) Low is onwave top

2) Wave top is pointing tocold air

3) Cold air ismoving S,warm air ismoving N

(NH)*Cold air is heavier than warm air!!! *

L


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CAE NLS sect5 TB 25

VERTICALE DOORSNEDE DOOR EEN FRONTALE GOLF TOONT DE VERDELING VAN WARME EN KOUDE LUCHT

h

EN

W

S

warme luchtkoudelucht koude

lucht


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CAE NLS sect5 TB 26

VERANDERING VAN HET ISOBARENPATROON ROND EENVORMENDE FRONTALE GOLF

1005

1010

1010

1005

1000


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CAE NLS sect5 TB 27

AFSTAND/HOOGTE-VERHOUDING BIJ EEN HELLING VAN1:200

F R O N T V LA K


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CAE NLS sect5 TB 28

The symbols along the front are always situated in thedirection of movement of the front.

When there is little or no change in position, when thereis no movement of one air mass compared with the other,the front is said quasi-stationary or stationary .


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CAE NLS sect5 TB 29

FRONTS and there MOVEMENTS

SURFACE

COLD WARM

Which front?

Coldfront!! (CF)


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CAE NLS sect5 TB 30

FRONTS and there MOVEMENTS

SURFACE

COLD WARM

Which front?

Warmfront (WF)


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CAE NLS sect5 TB 31

Oefening fronten kleuren


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CAE NLS sect5 TB 32

Occlusions

SURFACE

COLD

WARM

1) Coldfront is less sloping than warmfront

2) Coldfront is moving faster (in same gradient) than warmfront(more cold airmass properties, less friction)

So warm sector becomes smaller

COLD


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CAE NLS sect5 TB 33

Occlusions

SURFACE

COLD

WARM

COLD

CF overtakes WF Occlusion proces starts

Resulting in two possibilities:

1.

CF occlusion WF occlusion

2.

W WCC CCC C

Occlusions


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CAE NLS sect5 TB 34

1.

CF occlusion: sfc front is CF WF occlusion. sfc front is WF

2.Occlusions

CCCC

CC

CC

CC

CC


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CAE NLS sect5 TB 35

When the coldest air (CC) is situated in advance of the warm front,the warm front remains on the surface, while the cold front is

lifted along the warm frontal surface, with the formation of awarm front occlusion . The cold front becomes an upper cold

front .

Warm front occlusion


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CAE NLS sect5 TB 36

When the coldest air (CC) is situated at the rear of the coldfront, the cold front remains in contact with the surface, whilethe warm front is lifted along the cold frontal surface, with theformation of a cold front occlusion . The warm front is now anupper warm front .

Cold front occlusion


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CAE NLS sect5 TB 37


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CAE NLS sect5 TB 38


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CAE NLS sect5 TB 39

Frontal inversion


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CAE NLS sect5 TB 40

DE FRONTALE INVERSIE

WARM

KOUD


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CAE NLS sect5 TB 41

Geographical classification of fronts

030

30

45

45

70

70

A

AA = arctic air

P

P

P = polar air

T

T

T = tropical air

E

E

E = equatorial air

Arctic front

Arctic front

Polar front

Polar front

Subtropical front

Subtropical front

Intertropical front*


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CAE NLS sect5 TB 42

ARCTISCHE FRONTARCTISCHE FRONT arctische lucht en polaire luchtarctische lucht en polaire lucht

POLAIRE FRONTPOLAIRE FRONT polaire lucht en tropische luchtpolaire lucht en tropische lucht

TROPISCHE FRONTTROPISCHE FRONT tropische lucht en equatoriale luchttropische lucht en equatoriale lucht

INTER TROPISCHE CONVERGENTIE ZONEINTER TROPISCHE CONVERGENTIE ZONE equatoriale lucht noordelijk halfrond en equatorialeequatoriale lucht noordelijk halfrond en equatoriale

lucht zuidelijk halfrondlucht zuidelijk halfrond

GEOGRAFISCHE INDELINGGEOGRAFISCHE INDELING


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CAE NLS sect5 TB 43

Pressure and wind shift on fronts (page 5-15)


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CAE NLS sect5 TB 44

Pressure falling at approaching warmfront due to replacement of cold (heavy) air by warm (light) air due to lifting of fast amounts of air

Strong pressure drop


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CAE NLS sect5 TB 45

Coldfront

1010

1015

H igh pressure

L ow pressure

Wind?Wind?

N

SW

W


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CAE NLS sect5 TB 48Sheet 48


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CAE NLS sect5 TB 49

CONCLUSIONS:

There is a kink of the isobars along the front towardshigher pressure.

The wind veers at the passage of a front in the northern

hemisphere.There is an isallobaric minimum and upgliding ahead of the warm front.

There is an isallobaric maximum and subsidence at therear of the cold front.


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CAE NLS sect5 TB 50

X G F E D C B A XX X X X X X X

L

H

18.000

6000FZL

SFC

1010

1015

1020

10051000995


21 j i 12 t Th l f


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CAE NLS sect5 TB 51


L

H

6 km

2 kmFZL

SFC

1010

1015

1020

10051000995


21 juni 12 utc The polar front

pressure:

A

1021 hPaWind: 24005 kt.

clouds: Cs/Cu

precipetation:dry

airmass: PL

T/Td: 15/10 C

visibility: good

Stability: unstabele

FZL: low


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CAE NLS sect5 TB 52


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CAE NLS sect5 TB 53

21 juni 12 utc Th l f t


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CAE NLS sect5 TB 54


L

H

6 km

2 kmFZL

SFC

1010

1015

1020

10051000995



pressure:

B

1018 hPaWind:18010 kt.

clouds: As/Ns

precipetation:rain

airmass: PL

T/Td: 14/11 C

visibility: less

Stability: Morestable

FZL: low


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CAE NLS sect5 TB 55

21 juni 12 utc Th l f t


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CAE NLS sect5 TB 56


L

H

6 km

2 kmFZL

SFC

1010

1015

1020

10051000995



pressure:

C


clouds: Sc/St

precipetation: rain

airmass: PL

T/Td: 13/12 C

visibility: bad

Stability: stable

FZL: high


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CAE NLS sect5 TB 57

21 juni 12 utc the polar front


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CAE NLS sect5 TB 58


L

H

6 km

2 kmFZL

SFC

1010

1015

1020

10051000995


21 juni 12 utc the polar front

pressure:

D

1012 hPaWind: 24012 kt.

clouds: Sc/Ac

precipetation:dry

Airmass: TL

T/Td: 20/15 C

visibility: better

Stability: unstable

FZL: high


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CAE NLS sect5 TB 59



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CAE NLS sect5 TB 60


L

H

6 km

2 kmFZL

SFC

1010

1015

1020

10051000995



pressure:

E

1012 hPaWind: 24012 kt.

clouds: St/Sc/As

precipetation: rain

airmass: TL

T/Td: 19/16 C

visibility: less

Stability:More stable

FZL: high


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CAE NLS sect5 TB 61



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CAE NLS sect5 TB 62


L

H

6 km

2 kmFZL

SFC

1010

1015

1020

10051000995



pressure:

F


clouds: Ci Cu/Cb

precipetation: dry showe

airmass: PL

T/Td: 10/05 C

visibility: good bad

Stability: unstable

FZL: lowest


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CAE NLS sect5 TB 63


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CAE NLS sect5 TB 65


L

H

6 km

2 kmFZL

SFC

1010

1015

1020

10051000995


j The polar front

pressure:

G

1017 hPaWind: 18005 kt.

clouds: Cu

precipetation:dry

airmass: PL

T/Td: 11/05 C

visibility: good

Stability: unstable

FZL: lowest


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CAE NLS sect5 TB 66

At which airport is the following weather development taking place?TAF 060600Z 060716 25006KT 8000 BKN240 BECMG 0710 OVC200


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CAE NLS sect5 TB 67

TAF 060600Z 060716 25006KT 8000 BKN240 BECMG 0710 OVC200BECMG 1013 23010KT 8000 OVC100 BECMG 1316 23014KT 6000RA SCT030 OVC050=

SFC 06Z

A B C D E F G


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CAE NLS sect5 TB 68

A B C D E F G

Pressure 1021 hPa 1018 hPa 1015 hPa 1012 hPa 1012 hPa 1016 hPa 1017 hPa

Wind ZW 5kt ZZW10kt ZZO15kt ZW 12kt ZW 12kt WNW 10 Z 5kt

Clouds Cs/Cu As/Ns Sc/St Sc/Ac St/Sc/As Cs Cu/Cb Cu

precipetation Dry Rain Rain Dry Rain Dry/shower dry

aitmass PL PL PL TL TL PL PL

T/Td 15/10C 14/11 C 13/12 C 20/15 C 19/16 C 10/05 C 11/05 C

stability unstablemoreStable Stable unstable More

stableunstable unstable

visibility Good Less bad better less Good/bad good


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CAE NLS sect5 TB 69

Conclusions:

approching warmfront: dropping pressure backing and increasing wind

Lowering cloudbase

starting to rain visibility decreasing

Passing warmfront: veering of wind

rising of temperature

some breaks in clouds


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CAE NLS sect5 TB 70

Conclusions:

Approaching coldfront: clouds increasing fast

greater intensity of rain

Passing coldfront: pressure rising

veering of wind

breaking of clouds

dry/shower

falling of temperature


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CAE NLS sect5 TB 71

Frontogenesis and frontolyse

Definition:

Frontogenesi s is the initial formation or the intensificationof a frontal surface or front.

Frontolysis is the dissipation or weakening of a frontal surface or front.


72/81

COL


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CAE NLS sect5 TB 73

frontolyse

H

H

LL

COL

Inflow axis

Along Inflow axis !!!

Fig 5.26 page 5.24


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CAE NLS sect5 TB 74

MIND YOU 1: Warm land = Summer, Spring

Cold land = Winter, fall

MIND YOU 2 : relative temperatures!!

Life cycle of a mid latitude low


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CAE NLS sect5 TB 75


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CAE NLS sect5 TB 76

Een mooi simpel voorbeeld


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CAE NLS sect5 TB 77

Back-bent occlusion (fig.5.31)

Back-bent occlusion acts as a coldfront !

I fl f i f l


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CAE NLS sect5 TB 78

Influence of mountainous area on a frontal passage

Influence of a mountain barrier on a warm front passage: The WF

becomes a upper front!

The cold air at the surface, is hard to remove*

EEN WARMTEFRONT GLIJDT OVER EEN KOUDE


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CAE NLS sect5 TB 79

PLAKLAAG

KKKK KK KK

H

Often in winter: cold air is heavy, strong friction!

Influence of mountainous area on a frontal passage


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CAE NLS sect5 TB 80

Influence of a mountain barrier on a cold front passage:no or little influence!


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Depressie familie

Documents

Section 5 TB super slides meteorology