Section 7 TB meteo

7/28/2019 Section 7 TB meteo

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CAE NLS TB sect7 1

Wat doet de wind? En waarom.?


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CAE NLS TB sect7 2


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CAE NLS TB sect7 3

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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CAE NLS TB sect7 4

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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CAE NLS TB sect7 5

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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CAE NLS TB sect7 9

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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CAE NLS TB sect7 14

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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CAE NLS TB sect7 18

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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CAE NLS TB sect7 21

Vth=Vboven -Vonder

Vbo

VOnd

Vbo

VOnd

Vth

300hPa

500hPa


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CAE NLS TB sect7 22

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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CAE NLS TB sect7 24

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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CAE NLS TB sect7 25

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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CAE NLS TB sect7 28

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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CAE NLS TB sect7 31

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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CAE NLS TB sect7 40

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



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CAE NLS TB sect7 45

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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CAE NLS TB sect7 46

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


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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Section 7 TB meteo

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