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Analysis of the potential vorticity budget of a tropopause polar cyclone. Steven M. Cavallo and Gregory J. Hakim. University of Washington Department of Atmospheric Sciences. Outline. Tropopause polar vortices (TPVs) Ertel potential vorticity (EPV) Tropopause maps November 2005 TPV - PowerPoint PPT Presentation
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10/25/2006 13th Cyclone Workshop 1
Analysis of the potential vorticity budget of a tropopause polar
cyclone
Steven M. Cavallo
and Gregory J. Hakim
University of Washington
Department of Atmospheric Sciences
10/25/2006 13th Cyclone Workshop 2
Outline•Tropopause polar vortices (TPVs)
•Ertel potential vorticity (EPV)
•Tropopause maps
•November 2005 TPV
•PV budget of November 2005 TPV
10/25/2006 13th Cyclone Workshop 3
Waves and vortices
Vortex
Wave
•Consider a materially conserved field such as potential vorticity (PV):
Linear solutions are waves, nonlinear are vortices
•Observations tell us that upper level disturbances are more wave-like near jet stream and vortex-like away from jet stream
10/25/2006 13th Cyclone Workshop 4
Waves and vortices
• Closed contours in a materially conserved field:Fluid parcels are bound by closed contours of that field
•Using potential vorticity (PV), changes in vortex strength can be assessed by changes in fluid properties within these closed contours
These vortices often drift into mid-latitudes, sometimes triggering surface cyclogenesis
10/25/2006 13th Cyclone Workshop 5
Tropopause polar vortices (TPVs)Tropopause polar vortices (TPVs) are:
•Vortices that occur well poleward of the jet stream
•Based on the tropopause
•Cold core
Although there is considerable understanding about the life cycles of surface extratropical cyclones, relatively less is known about the upper-level disturbances governing them
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Radiational cooling at cloud top
Radiational heating at cloud base
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Heating Profile EPV Changes
10/25/2006 13th Cyclone Workshop 9
Heating Profile EPV Changes
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Potential Vorticity & Isentropic Surfaces
PV surfaces (black) in PVU, isentropic surfaces (red) in Kelvin
1 PVU = potential vorticity unit = m2 K kg-1 s-1
(Adapted from Hoskins 1990)
10/25/2006 13th Cyclone Workshop 11
November 2005 TPV
GFS analysis tropopause pressure Coral Harbour, NT sounding
21 November 2005 at 00 UTC
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November 2005 TPV
GFS analysis tropopause pressure Coral Harbour, NT sounding
22 November 2005 at 00 UTC
10/25/2006 13th Cyclone Workshop 13
November 2005 TPV
GFS analysis tropopause pressure Coral Harbour, NT sounding
23 November 2005 at 00 UTC
10/25/2006 13th Cyclone Workshop 14
November 2005 TPV
GFS analysis tropopause pressure Coral Harbour, NT sounding
24 November 2005 at 00 UTC
10/25/2006 13th Cyclone Workshop 15
November 2005 TPV
•Horizontal grid spacing 30 km, 31 vertical levels
•5-class microphysics, RRTM longwave radiation
•GFS analysis and boundaries updated every three hours
WRF simulations:
10/25/2006 13th Cyclone Workshop 16
Siberia
Averages within 285 K closed contour
10/25/2006 13th Cyclone Workshop 17
Siberia
Averages within 285 K closed contour
10/25/2006 13th Cyclone Workshop 18
Siberia
Averages within 285 K closed contour
10/25/2006 13th Cyclone Workshop 19
Hudson Bay
Averages within 280 K closed contour
10/25/2006 13th Cyclone Workshop 20
Hudson Bay
Values at center of vortex
10/25/2006 13th Cyclone Workshop 21
Siberia
EPV terms Diabatic components
10/25/2006 13th Cyclone Workshop 22
Hudson Bay
EPV terms Diabatic components
10/25/2006 13th Cyclone Workshop 23
Summary
•TPV strengthening from cloud-top radiational cooling
•TPV weakening processes not as clear, but weakening appears to occur when latent heating effects dominate the radiational effects
•What is the contribution of the frictional component? To what degree is implicit model diffusion effecting the budget closure?
10/25/2006 13th Cyclone Workshop 24
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10/25/2006 13th Cyclone Workshop 27
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