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Potential Vorticity. Barotropic Instability. Water Vapor Loop. President’s Day. http://www.atmos.washington.edu/academic/videos/PresidentsDayStorm.html. http://www.atmos.albany.edu/daes/atmclasses/atm305/climomaps.html. Positive PV Anomaly Near Trop. Negative PV Anomaly Near Trop. - PowerPoint PPT Presentation
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Potential Vorticity
Barotropic Instability
• Water Vapor Loop
President’s Day
• http://www.atmos.washington.edu/academic/videos/PresidentsDayStorm.html
http://www.atmos.albany.edu/daes/atmclasses/atm305/climomaps.html
Positive PV Anomaly Near Trop
Negative PV Anomaly Near Trop
Surface +PV Anomaly
Piecewise PV Inversion
Stoelinga 1996: Overheads
Lee Troughing and PV
• Conservation of potential vorticity
– conserved for adiabatic frictionless motion• Ratio of absolute vorticity and depth of vortex
(Holton 2004, p. 96)
p
gfP Ertel Potential Vorticity
• Conservation of potential vorticity
– for a homogeneous incompressible fluid• evaluated at constant height
(Holton 2004, p. 96)
Const/ hfP z Potential Vorticity
• Conservation of potential vorticity– When the depth of the vortex
changes following motion, its absolute vorticity must change to maintain conservation of potential vorticity (Holton 2004, p. 98)
• Conservation of potential vorticity– For westerly flow impinging on
an infinitely long mountain range…
• (a) upstream, zonal flow is uniform (u/y = 0, v=0), = 0
• (b) deflection of upper surface upstream of barrier increases h absolute vorticity must increase air column turns cyclonically
(Holton 2004, p. 98)
(a) (b) (c) (d) (e)
• Conservation of potential vorticity– For westerly flow impinging on
an infinitely long mountain range…
• poleward drift in (b) also causes increase in f
• (c) as column crosses mountain, h decreases absolute vorticity must decrease becomes negative air column drifts equatorward
ATMS 316- Background
(Holton 2004, p. 98)
(a) (b) (c) (d) (e)
• Conservation of potential vorticity– For westerly flow impinging on
an infinitely long mountain range…
• equatorward drift in (c) also causes decrease in f
• (d) as column crosses mountain, h increases absolute vorticity must increase becomes positive air column drifts poleward
(a) (b) (c) (d) (e)
• Conservation of potential vorticity– For westerly flow impinging on
an infinitely long mountain range…
• (e) alternating series of ridges and troughs downstream of mountain range
• cyclonic flow pattern immediately to the east of the mountains (lee side trough)
ATMS 316- Background(a) (b) (c) (d) (e)
(Ahrens 2005, p. 222)
• Lee cyclogenesis– Preferred regions of
cyclogenesis• Alps
– Narrow mountain range
– Theory that applies to Alps lee cyclogenesis is modifed from that used to describe lee cyclogenesis of the Rockies
– Ageostrophic effects dominate and the modification of baroclinic instability by the Alps is more difficult to analyze
Alps and Smaller Ranges More Complicated With All Kinds of
Baroclinic Effects
Tropopause +PV anomalies often apparent in water vapor imagery
Trop Pressure
Terminology: PV Streamer• A PV-streamer is an elongated band of potential vorticity, generally
in the upper troposphere. It is mesoscale in width and synoptic scale in length.
• In the upper troposphere, they are associated with stratospheric–tropospheric mass exchange, particularly in the area where the tropopause folds.
The End