midlatitude cyclones - chapter 10kestrel.nmt.edu/~sessions/phys189/ab_ch10.pdf · cyclones phys 189...

MidlatitudeCyclones

PHYS 189

MidlatitudeCyclone life cycle

Rossby waves,vorticity, &cyclogenesis

Surface fronts andupper levelpatterns

Conveyor Belts &midlatitudecyclones

Midlatitude Cyclone life cycle

Relation of fronts in a midlatitude cyclone

PHYS 189 () Midlatitude Cyclones week 11 1 / 40

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Polar Front theory

Though cyclogenesis of mid-latitude cyclones do not alwaysoccur along the polar front, those that do can be describedby the Polar front theory


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Clicker question

What type of front is shown in this diagram?A. warm

B. cold

C. stationary

D. occluded


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Clicker question

What is the term for this stage in the life cycle of a midlatitudecyclone?

A. cyclogenesis

B. occlusion

C. maturity

D. senescence


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Approaching maturity

Rotation from the initial kink in the stationary front creates aweak low pressure system which deepens. At this stage, thereare distinct warm and cold fronts.

I convergence occurs at the low pressure region

I convection along frontal boundaries create bands ofclouds


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Mature midlatitude cycloneClicker question

In which area would over-running occur?

D

C

A

B


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What is the primarymechanism for uplift atA?

A. overrunning

B. convergence

C. localized instability

D

C

A

B


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Why are the cloud bandwidths so different at thewarm and cold fronts?


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Clicker question

An occlusion representsA. cyclogenesis

B. cyclone intensification

C. gradual death of cyclone

D. none of the above


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Looking for midlatitude cyclones

I current US weather

I Current European weather

I cartoon 1

I cartoon 2

I weather data &forecast


http://www.hpc.ncep.noaa.gov/HTML/sfc2.shtml

http://www.eurometeo.com/english/maps

http://www.physics.nmt.edu/Department/homedirlinks/sessions/phys189/ch10/ch10_Tutorials/Midlatitude_Cyclones/Cyclone_Form_Movement.html

http://www.physics.nmt.edu/Department/homedirlinks/sessions/phys189/ch10/ch10_Tutorials/Midlatitude_Cyclones/Cyclone_Basics_Fronts.html

http://weather.rap.ucar.edu

http://weather.rap.ucar.edu

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Rossby waves, vorticity, & cyclogenesis

Rossby Waves

Rossby waves can generate anomalous temperatures in the mid-dle and high latitudes


http://www.physics.nmt.edu/Department/homedirlinks/sessions/phys189/ch08/ch08_Tutorials/Upper_Level_Pressure_and_Winds/West_Winds_Wave_Motion.html

http://www.physics.nmt.edu/Department/homedirlinks/sessions/phys189/ch08/ch08_Tutorials/Upper_Level_Pressure_and_Winds/West_Winds_Wave_Motion.html

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Rossby wave

Rossby waves initiate rotation in the fluid.This rotation is called vorticity.


MidlatitudeCyclones

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Rossby wave

Rossby waves initiate rotation in the fluid.

This rotation is called vorticity.


MidlatitudeCyclones

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Rossby wave

Rossby waves initiate rotation in the fluid.This rotation is called vorticity.


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Vorticity

vorticity: rotation in a fluid (ζ, zeta)

relative vorticity: vorticity relative to Earth’s surface

Earth vorticity: vorticity which depends on the rotation ofthe earth about it’s axis; depends on latitudeonly

absolute vorticity: sum of both relative and Earth vorticity =the overall rotation of the fluid

positive vorticity: counterclockwise in NH; clockwise in SH

negative vorticity: counterclockwise in SH; clockwise in NH

Vorticity is actually a vector (like angular momentum),whose direction points along the thumb of your right hand inNH; your fingers move in the direction of the fluid


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Clicker question

The value of the Earth vorticity at the equator is

A. maximum

B. zero

C. cannot be determined without more information


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Clicker question

Clockwise rotation relative to the Earth’s surface in thesouthern hemisphere

A. partially cancels the Earth vorticity and decreases theabsolute vorticity

B. increases the absolute vorticity since it enhances fluidrotation in the same direction as the Earth vorticity

C. doesn’t give a notable difference to the absolutevorticity compared to counterclockwise rotation.


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Clicker question

The maximum in absolute vorticityA. occurs around the low pressure region

B. occurs around the high pressure region

C. is the same for both the high and low pressure regions

D. cannot be determined without more information


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Clicker question

The NH air shown in segment 1 hasA. positive relative vorticity

B. negative relative vorticity

C. zero relative vorticity


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Clicker question

The NH air shown in segment 2 hasA. positive relative vorticity

B. negative relative vorticity

C. zero relative vorticity


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Recall angular momentum

angular momentum increases asthe can convergesvorticity works the same way:increases in vorticity correspondto converges; decreases give di-vergence


MidlatitudeCyclones

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angular momentum increases asthe can converges

vorticity works the same way:increases in vorticity correspondto converges; decreases give di-vergence


MidlatitudeCyclones

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angular momentum increases asthe can convergesvorticity works the same way:increases in vorticity correspondto converges; decreases give di-vergence


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Vorticity and divergence

Changes in vorticity induce convergence/divergences:

−1

ζ

∆ζ

∆t= div

I div=divergence

I increases in vorticity (∆ζ > 0) give convergence

I decreases in vorticity (∆ζ < 0) give divergence

I What does div < 0 mean?


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−1

ζ

∆ζ

∆t= div

I div=divergence

I increases in vorticity (∆ζ > 0) give

convergence




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−1

ζ

∆ζ

∆t= div

I div=divergence


I decreases in vorticity (∆ζ < 0) give

divergence



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−1

ζ

∆ζ

∆t= div

I div=divergence





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How vorticity changes result in high and lowsurface pressures

Is this upper, lower, or middle troposphere?

Where can we expect convergence & divergence?


MidlatitudeCyclones

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Is this upper, lower, or middle troposphere?Where can we expect convergence & divergence?


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MidlatitudeCyclones

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Clicker question

Surface low-pressure systems resulting from uppertropospheric motions are called

A. dynamic lows

B. cold core lows

C. thermal lows

D. warm core lows

E. A and B, OR C and D


MidlatitudeCyclones

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Clicker question

Surface low-pressure systems resulting from localized heatingfrom below are called

A. dynamic lows

B. cold core lows

C. thermal lows

D. warm core lows

E. A and B, OR C and D


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Clicker question

Which of the following structures corresponds to a warm coreand which is a cold core?

H

L L

L

warm cold


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Absolute vorticity at 500 mb heights(mid-troposphere)


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Clicker question

Relative vorticity can be induced by

A. curvature of the flow

B. shear

C. a change in Earth vorticity

D. all of the above


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Vorticity

ζabsolute = ζEarth + ζrelative


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Clicker question

Which of the following statements is true?

A. Upper tropospheric air can influence surface weatherpatterns, but not vice-versa.

B. Surface weather patterns can influence uppertropospheric air, but not vice-versa.

C. Surface weather patterns can influence uppertropospheric air, and upper tropospheric air caninfluence surface weather.

D. WTF?


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Surface fronts and upper level patterns

How cold fronts at the surface generate upperlevel troughs

Assume pressure at the surfaceat A, B, and C is 1000 mb


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Clicker question

The 500 mb height con-tours in (a) are primarily

A. zonal

B. meridional


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Clicker question

The 500 mb height con-tours in (b) are primarily

A. zonal

B. meridional


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Clicker question

Which flow patter islikely associated withlight winds, calm con-ditions, and no areasof widespread precipita-tion?

A. zonal

B. meridional


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Weather break

I Real time 500 mb heights


http://weather.rap.ucar.edu/

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Clicker question

Midlatitude cyclones generally migrate

A. west-to-east

B. east-to-west

C. north-to-south

D. south-to-north

E. in an arbitrary direction


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Typical winter storm paths


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Migration of cyclone relative to Rossby wave


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Conveyor Belts & midlatitude cyclones

Conveyor belt model

I Cyclones are 3-dimensional entities that connect flowpatterns in the upper atmosphere with those at thesurface.

I the overall flows can be modeled by three flows orconveyor belts

I warm conveyor beltI cold conveyor beltI dry conveyor belt


MidlatitudeCyclones

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The Atmosphere

conveyor belt tutorial


http://www.physics.nmt.edu/Department/homedirlinks/sessions/phys189/ch10/ch10_Tutorials/Midlatitude_Cyclones/3D_Motion_Within_Cyclones.html

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Effects of climate change

Research indicates that the increase in global temperaturesassociated with increases in greenhouse gases have shiftedstorm tracks poleward.

⇒ The relative dry areas in the southwest could lose animportant source of moisture and suffer more droughts.


midlatitude cyclones - chapter 10kestrel.nmt.edu/~sessions/phys189/ab_ch10.pdf · cyclones phys 189...

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