chapter 10: middle latitude cyclones chapter 10: mid-latitude cyclones most active weather is...

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Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here we will examine how these systems evolve: Life cycle Bring the ingredients together for active weather Central U.S. focus.

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Page 1: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Chapter 10: Mid-latitude Cyclones

Most active weather is associated with a cyclone (i.e. low pressure system)

Here we will examine how these systems evolve:

Life cycle Bring the ingredients together for active

weather Central U.S. focus.

Page 2: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Hydrostatic Equilibrium

To create low pressure, the mass in the air column must be reduced.

At the surface low pressure systems have convergence … a build up of air in the column

To compensate the surface low must have support .... upper level support

Page 3: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Upper Level SupportConvergence at the surface must be compensated by divergence aloft

Divergence aloft = upper level support

For the system to intensify divergence aloft must be greater than surface convergence

Page 4: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Intensifying Mid-latitude Cyclone

L

Jet Stream

Surface Low

Slow

FastTrough

Page 5: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Intensifying Cyclones Characteristics Surface low is between trough and ridge

Westward tilt with height of system Jet forms on boundary between warm and

cold air and surface low is on that boundary The circulation around the surface low

introduces: Warm air advection (i.e., warm front) out

ahead of the low Cold air advection (i.e., cold front)

dragging behind the low

Page 6: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Intensifying Mid-latitude Cyclone

L

Warm Front

Cold Front

We anticipate these locations for the fronts.

The exact locations depend upon the situation

Warm Sector

Page 7: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Mid-latitude Cyclones

The pattern we have examined so far is point of most rapid intensification

How do we get to that point? How does the system dissipate

What is the life cycle of a low pressure system?

Page 8: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Mid-latitude Cyclone Life-CycleSurface – Initiation Stage

Page 9: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Mid-latitude Cyclone Life-CycleSurface – Intensification Stage

Page 10: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Mid-latitude Cyclone Life-CycleSurface – Cont. Intensification

Page 11: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Mid-latitude Cyclone Life-CycleSurface – Occlusion Stage

Page 12: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Mid-latitude Cyclone Life-Cycle The surface system propagates (moves)

during its life cycle The surface interacts with the upper levels

Upper levels support the surface Near surface circulations redistribute the

warm/cold air which causes the jet to adjust.

Now that we have looked at the surface, lets consider both surface and upper levels

Page 13: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Intensifying Mid-latitude Cyclone

L

Jet Stream

Surface Low

Cold Air Advection

Warm Air Advection

Dashed lines represent locations at a later time

Page 14: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Intensifying Mid-latitude Cyclone

LJet Stream

Surface Low

Cold Air Advection

Warm Air Advection

L

Dashed lines represent locations at a later time

Page 15: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Intensifying Mid-latitude Cyclone

L

Jet Stream

Surface Low

Cold Air Advection

Warm Air Advection

Dashed lines represent locations at a later time

Page 16: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Page 17: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Page 18: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Mid-latitude Cyclones These systems move mainly west to east

Some move NW → SW, some SW → NE The track is often tied to the jet stream

pattern Often a location will first experience the

warm front and then the cold front Some have strong intensification others

don't Some systems go through the life-cycle

quickly (3-5 days), or not (7-10 days)

Page 19: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Mid-latitude Cyclone Weather

Page 20: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

High Pressure Systems

Form in the middle of air masses not on the boundaries

Have no systematic life-cycle Work with rather than against gravity so no

need for upper level support Though upper level convergence can

generate high pressure

Page 21: Chapter 10: Middle Latitude Cyclones Chapter 10: Mid-latitude Cyclones Most active weather is associated with a cyclone (i.e. low pressure system) Here

Chapter 10: Middle Latitude Cyclones

Main Points Dropping pressure requires a loss of mass

in the column Systems only deepen if they have upper-

level support Systems have self-development/life cycle

Surface affects upper-levels Upper levels affect surface

Developing systems tilt westward with height