Cyclogenesis and cyclolysis
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Cyclogenesis and Cyclolysis. ATS 113. What We’ll Learn:. The Polar Front causes the Midlatitude Jet Stream (by the Thermal Wind Relationship). The MLJ has troughs and ridges. Troughs and ridges lead to patterns of divergence aloft, causing low pressure at the surface. Midlatitude Jet Stream.

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What we ll learn l.jpg
What We’ll Learn:

  • The Polar Front causes the Midlatitude Jet Stream (by the Thermal Wind Relationship).

  • The MLJ has troughs and ridges.

  • Troughs and ridges lead to patterns of divergence aloft, causing low pressure at the surface.



Slide4 l.jpg

400mb

A

500mb

300mb

B

400mb

600mb

500mb

POLAR FRONT

North

COLD

South

WARM


Zonal l.jpg
“Zonal” Wind Relationship.


Meridional l.jpg
“Meridional” Wind Relationship.



Troughs and ridges l.jpg
“Troughs” and “Ridges” Wind Relationship.


Vorticity l.jpg

L Wind Relationship.

Vorticity

  • The “spin of the wind”.

  • Defined so that CYCLONIC is POSITIVE.




Between has no vorticity l.jpg
Between has no vorticity. Wind Relationship.



Nva ahead of ridge pva ahead of trough l.jpg
NVA ahead of ridge, Wind Relationship.PVA ahead of trough

PVA

NVA


What is pva l.jpg
What is PVA? Wind Relationship.

  • The process by which the winds are bringing air that has higher vorticity values.

Location A has positive vorticity.

Location B has no vorticity but does have “positive vorticity advection”.

B

A


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What is PVA? Wind Relationship.

  • As air moves from location A to location B, it needs to lose its spin.

B

A


Losing spin l.jpg
Losing spin Wind Relationship.

  • How does a spinning figure skater lose his spin?


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Losing spin Wind Relationship.

  • How does a spinning figure skater lose his spin?

  • Spreading his arms!


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So… Wind Relationship.

  • Spreading out is a way of losing spin.


A region with pva is a location in which the air must lose its spin l.jpg
A region with PVA is a location in which the air must Wind Relationship.lose its spin!

PVA


Divergence l.jpg
DIVERGENCE! Wind Relationship.


Down at the surface l.jpg
Down at the surface… Wind Relationship.


Upper level divergence l.jpg
…upper level divergence… Wind Relationship.

divergence


Means low pressure at the surface l.jpg
…means low pressure at the surface! Wind Relationship.

divergence

L


Notice where the low is l.jpg
Notice where the low is: Wind Relationship.

East of the trough

West of the ridge

In the region of positive vorticity advection!

divergence

L


Notice where the low is26 l.jpg
Notice where the low is: Wind Relationship.

East of the trough

West of the ridge

In the region of positive vorticity advection!

L


Notice where the low is27 l.jpg
Notice where the low is: Wind Relationship.

L

East of the trough

West of the ridge

In the region of positive vorticity advection!













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Birth and Death jet to be here!

  • Cyclogenesis:

    • Strengthening a cyclone by lowering its pressure.

    • Happens when PVA in the jet stream causes upper level divergence.

  • Cyclolysis:

    • Weakening a cyclone by increasing its pressure.

    • Happens when the jet stream is no longer directly above the low due to the formation of an occluded front.


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Real Life Examples: jet to be here!

Jet stream has a very sharp trough in the midwest.


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Real Life Examples: jet to be here!

Positive vorticity in trough; negative vorticity in ridge.


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Real Life Examples: jet to be here!

Positive Vorticity Advection near Detroit


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Real Life Examples: jet to be here!

A strong low near Detroit!


Another example l.jpg
Another Example: jet to be here!

A huge trough in the Rockies.


Another example45 l.jpg
Another Example: jet to be here!

Positive Vorticity in the trough.


Another example46 l.jpg
Another Example: jet to be here!

Positive Vorticity Advection ahead of the trough.


Another example47 l.jpg
Another Example: jet to be here!

L

A low and precipitation at the surface!