Section 5 TB super slides meteorology
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Transcript of Section 5 TB super slides meteorology
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CAE NLS sect5 TB 1
5. Airmasses and fronts
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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.
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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
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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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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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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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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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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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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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Embedded CB
Movement of front
ColdWarm FZL
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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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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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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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FRONTS and there MOVEMENTS
SURFACE
COLD WARM
Which front?
Coldfront!! (CF)
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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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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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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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1.
CF occlusion: sfc front is CF WF occlusion. sfc front is WF
2.Occlusions
CCCC
CC
CC
CC
CC
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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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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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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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Pressure and wind shift on fronts (page 5-15)
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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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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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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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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
X G F E D C B A XX X X X X X X
21 j i 12 t Th l f
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X G F E D C B A XX X X X X X X
L
H
6 km
2 kmFZL
SFC
1010
1015
1020
10051000995
X G F E D C B A XX X X X X X X
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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21 juni 12 utc Th l f t
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X G F E D C B A XX X X X X X X
L
H
6 km
2 kmFZL
SFC
1010
1015
1020
10051000995
X G F E D C B A XX X X X X X X
21 juni 12 utc The polar front
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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21 juni 12 utc Th l f t
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X G F E D C B A XX X X X X X X
L
H
6 km
2 kmFZL
SFC
1010
1015
1020
10051000995
X G F E D C B A XX X X X X X X
21 juni 12 utc The polar front
pressure:
C
1015 hPaWind:16015 kt.
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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X G F E D C B A XX X X X X X X
L
H
6 km
2 kmFZL
SFC
1010
1015
1020
10051000995
X G F E D C B A XX X X X X X X
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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21 juni 12 utc The polar front
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X G F E D C B A XX X X X X X X
L
H
6 km
2 kmFZL
SFC
1010
1015
1020
10051000995
X G F E D C B A XX X X X X X X
21 juni 12 utc The polar front
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
21 juni 12 utc The polar front
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X G F E D C B A XX X X X X X X
L
H
6 km
2 kmFZL
SFC
1010
1015
1020
10051000995
X G F E D C B A XX X X X X X X
21 juni 12 utc The polar front
pressure:
F
1016 hPaWind:29010 kt.
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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21 juni 12 utc The polar front
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X G F E D C B A XX X X X X X X
L
H
6 km
2 kmFZL
SFC
1010
1015
1020
10051000995
X G F E D C B A XX X X X X X X
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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At which airport is the following weather development taking place?TAF 060600Z 060716 25006KT 8000 BKN240 BECMG 0710 OVC200
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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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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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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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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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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.
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COL
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frontolyse
H
H
LL
COL
Inflow axis
Along Inflow axis !!!
Fig 5.26 page 5.24
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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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Een mooi simpel voorbeeld
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Back-bent occlusion (fig.5.31)
Back-bent occlusion acts as a coldfront !
I fl f i f l
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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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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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Influence of a mountain barrier on a cold front passage:no or little influence!
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Depressie familie