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The Midlatitude Cyclone
The Wave Cyclone Model
(Norwegian model)
• Stationary Front
• Nascent Stage
• Mature Stage
• Partially Occluded Stage
• Occluded Stage
• Dissipated Stage
Stages of cyclone development
Low
High
What initiates cyclogenesis?
500-hPa height
What maintains the surface low?
Imagine a surface low forming below an upper level low.
Actual vertical structure:
Upper level low is tilted westward with height with respect to the surface.
UPPER LEVEL
DIVERGENCE
INITIATES AND
MAINTAINS A
SURFACE LOW.
A look at the large scale.
Where is upper level divergence most likely to occur?
Cyclone initiation: Passage of a shortwave often initiates the formation of a surface low.
Cyclone development: •baroclinic instability (baroclinic means temperature varies on an isobaric surface) causes initial ‘perturbation’ to grow. •occurs in the presence of strong temperature gradients.
Imagine a short wave trough passes overhead ( looking North ): Where will surface low develop?
Low (^) DIV High
east
( looking North ): Near the surface, where will we have cold and warm advection? Will this amplify or weaken the upper level low? How about the upper level divergence? Will a more intense upper level low strengthen or weaken the surface low?
LowLow (^) DIVDIV HighHigh
Low
cool warm
Cyclone development: Strong north south gradient+passage of a shortwave trough Can lead to rapid cyclogenisis via baroclinic instability (baroclinic means temperature varies on an isobaric surface)
Baroclinic instability •Upper level shortwave passes. •Upper level divergence -> sfc low. •Cold advection throughout lower troposphere. •Cold advection intensifies upper low. •Leads to more upper level divergence. •Intensifies sfc low.
ADVECTION IS
KEY.
