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Wat doet de wind? En waarom.?
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7. Jetstreams. A band of strong winds > 60kt
7.1 Thermische wind (Vth)
Pressure height in FL T (15-2xFL/10)
850 hPa FL50 +5
700 hPa FL100 -5500 hPa FL180 -21
400 hPa FL240 -33
300 hPa FL300 -45
250 hPa FL340 -53
200 hPa FL390 -56,5
150 hPa FL450 -56,5
Kennen! Blz 1-27
Tropopause
*
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Wind at certain FL due to pressure difference in
horizontal level
Pressure difference of 5 hPa in upperair gives not the
same velocity !!!!!
dxdpFg .
1
sin...2 vFc sin..2
g
geo
Fv
decreases with height Vgeo changes with height by
same pressure
difference
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Isohyps = line of same pressure AND same altitude. Intersection
lines of one pressure sfc with horizontal planes
Flying from A to B along the isohypses of 552 dam means:
* Flying at constant true altitude of 5520 m
* Flying in the 500 hPa pressure surface
* Flying with tail wind (NH), and in general with no cross wind.
C
Flying from A to C
till H true alt. increases
from H to C true alt.
decreases
still flying in the 500
hPa surface (FL180) !!!
first wind from SB, later
wind from port
In reality
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Fly from L to X on 300 hPa surface (FL 300!) What happens?
300 hPa
contours
X
L 9280 m true
X 9520 m true
Dif: 240 m
X = 240 higherStill on 300
hPa surface =
FL300
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Thickness lines connect points with equal distance
between two layers
If difference between 2 layers
thicker than standard warm air
thinner than standard cold air
500 hPa
300 hPa
Cold Warm
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h constant
300 hPa
= p constant Cold Warm
NH, sloping pressure surface (300 hPa)
Pressure at B > A
Pressure at B > A so Vgeo from B to A
Windspeed depending on hook Alpha!
A B
Wind ?
ABVgeo
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More gradient = more sloping = more wind!
Now we see
the isohypses
act like isobars!
Close together
= more wind !!
More slope!!
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V V VT top base
Thermal wind (VT)
Thermal wind is a vector(not a real wind) wich gives
the difference between the Vgeo at the bottom of a
layer and the Vgeo at the top of a layer.
Vbase
Vtop-Vbase
VT
VT
Verbind pijlpunten van
onder naar bovenOB= Vt
(Verschil-vector!)
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The thermal windis parallel to the isotherms of mean
temperature in the layer (or to the thickness lines) with the
cold air (low mean temperature or low thickness) to theleft if we have the thermal wind in the back and the warm
air(high mean temperature or high thickness) to the right,
in the N.H.
What is the real wind doing?
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Advection of cold or warm air (NH)
What is this real wind
doing? (base to top)
What is this real wind
doing? (base to top)
In a layer.!!!
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Cold
advection
CA=KA
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Thermal wind and the Westerlies at moderate latitudes.
VT on the northern hemisphere is west because
temperature decreases from equator to north pole
VT = Vtop - Vbase
Vtop = Vbase + VT
V1000 VT
V900
V900 VT
V800
Conclusion: wind increases with height and becomes mainly
westerly at higher levels when VT is normally directed (positive!)
800 hPa
900 hPa1000 hPa
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Vertical shear
VT is positive: VT is negative:
Normal situation Is not rare.!
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Diktekaart-thermische wind-
advectie
Warmte- en kou-advectie
Ruimen en krimpen van de wind metde hoogte.
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Koud
Warm
Dun
Dik
Koud
Warm
Vth NH
Vth ZH
KOU LINKS
KOU RECHTS
NP
ZP
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Vth=Vboven -Vonder
Aannemen:
Diktel i jnen lopen // aan de isothermen, DUS:
Vth waait // isothermen (op NH kou links)
(op NH warmte rechts)
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Vth=Vboven -Vonder
Dus teken van pijlpunt Vo naar pijlpunt Vb
Vb
Vo
-Vo R
Vth
Vth
VANONDERNAARBOVEN (OB)
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Vth=Vboven -Vonder
Vbo
VOnd
Vbo
VOnd
Vth
300hPa
500hPa
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Vo
A
B
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Positie A (dia 22)
Vo
Vb
(500hPa)
Vth
Koude kant
Warme kant
CAE NLS TB sect7 20
Vo
500hPa
wind
A
Bij A is KOU-ADVECTIE
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Positie B (dia 22)
CAE NLS TB sect7 20
Vo
500hPa
wind
A
Vo
Vb
(500hPa)
Bij B is WARMTE-ADVECTIE
Koude kant
Warme kant
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Samenvatting:
1) Thermische wind waait // isothermen
Op NH kou links, warmte rechts
Op ZH andersom
Echte wind NH :2) Krimpen naar boven= Kou-advectie
3) Ruimen naar boven = Warmte advectie
4) Als temperatuurverdeling meewerkt
(Vth is positief) neemt de wind van beneden
naar boven TOE! (anders af!!)
Uitleg Jetstream
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Uitleg Jetstream
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The jetstream
Definition:
Jet streamsare strong, narrow currents of air with speeds
greater than 60kts.
They are characterized by strong horizontal and vertical
windshear.Velocity in center(the jet core):
General about 100 kts
Over North Atlantic and Europe*: 200 ktsOver north west Pacific in winter: > 300 kts
A jet stream is usually some thousands of kms in length,
hundreds of kms in width and some kms in depth.
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Lenght scale: in this case
30 x 60 nm ~ 3500km
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Horizontal scale: in this
case 7x60 nm ~ 800 km
Stornoway
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Vertical scale Jetstream
Ca. 20.000ft6 km
in this case
Maxwind?
Level?
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Cross section of a jet stream:
Ca 5 km
Ca 500 km
And a few thousends km long..
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Noordelijke Zomer
zwakker,
noorderlijker
geen arctische jet
Equatoriale jet uit
oosten!
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The jetstream has the same direction as the VT
Jetstream in the back, cold air at left side and warm air at the right
In the figure, jetstream is coming towards us. (NH)
?
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Conclusions: The maximum wind speed, thejet co reof the jet stream, is found
- at the level ofequal HORIZONTAL temperature
- on the warm side of the frontal zone (in warm air!)
- at altitudes just above the tropopause of the cold air, beneath the
warm tropopause, in the tropopause break.
The projection of the core on the surface lies in the cold airmass*.
The jet is caused by strong horizontal temperature gradients,
concentrated near the boundaries of air masses (fronts).
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Clear air turbulance ( CAT )
The greatest risk of CAT is at the cold side of thejetstream.
Why??
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300 hPa is jet core (kern)
400 hPa is jet axis (as)
Jet core and axis
jet
Core: absolute maxwind of jet
Axis: maxwind on a certain level
100kt
80kt
What is the maxwind in the core?
And on 400 hPa?
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Jet STREAKS
Core
They travel in the jet core downwind with up to 20 kts.
120 kt
140 kt140 kt
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Classification of jet streams
Richting?
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1. The Arctic Jet
associated with the arctic front
influences the weather over Europe only in winter
jet core at around 60north
height of the core varies between 300 and 400hPa,
sometimes lower
wind speed reaches values between 75 and 130kt
direction is westerly
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2. The Polar Jet
associated with the polar front
observed all the year around
great variation between one jet and another
height of the core usually between 300 and 200 hPa
wind speed highly variable with on average 125kts in winter
and 65kts in summer
direction: all possible, Wly dominant
situated between 40 and 60N in winter and between 60
and 80N in summer
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Polar Jet is often interrupted. Parts with strong winds alternate
with intervals with weak winds.
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3. The Subtropical Jet
notassociated with a front ( keeping impulse moment)
between 25 and 40north in winter and 40-45north in summer
height of the core around 200 hPa
wind speed reaches values between 80kt in summer and
140ktin winter
direction is westerly
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4. The Equatorial Easterly Jet
notassociated with a front (temp. diff. at higher levels only)
between 12 and 15N only in summer NH
height of the core between 100 and 150 hPa
wind speed around 60kt, seldom 100kt
direction is easterly*
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Equatorial Easterly Jet in June-July-August
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5. The Polar Night Jet
notassociated with a front (temp. diff. at higher levels only)
near 70N and S in winter
height of the core near 25 hPa(80.000 ft)
wind speed around 60kt
direction is westerly
Temperatures up to70 on cruising levels!*
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CAE NLS TB sect7 48POSITIONS OF JET STREAMS IN THE NORTHERN HEMISPHERE
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Ad ti ?
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Advection?
568 572NH
Wind?-40
-45 No advection
Ad ti ?
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Advection?
568 572NH
Wind -40
-45
WAA
Ad ection?
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Advection?
568572NH Wind?
-40
-45
CAA
O f i W t f k d ti
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Oefening Warmte of kou-advectie
Bereken en/of teken Vth
Welke advectie, KA of WA
E i j d i
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Exercise:jetstream, advection, temps
draw isohypsen on 400 hPa chart (delta h = 4 dam)
draw istherms (in red or diff. Colour) (delta T = 5C)
where is CAA and where is WAA?
Temps
La Coruna 08001 Emden 10200
T 500 .. .
Tropopause .. .
T 36000`. .
Tsfc *
WX? .. ..
Advection?. .
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