Transcript Potential vorticity dynamics of a tropopause polar vortex Steven M. Cavallo

Potential vorticity dynamics of a
tropopause polar vortex
Steven M. Cavallo
and Gregory J. Hakim
University of Washington
Department of Atmospheric Sciences
25 June 2007
16th Conference on Atmospheric and Oceanic Fluid Dynamics
Outline
• Tropopause polar vortices (TPVs)
• Ertel Potential Vorticity (EPV)
• Mechanisms for vortex intensity changes
• November 2005 TPV
 Overview and observations
 Potential vorticity analysis
 PV budget
25 June 2007
16th Conference on Atmospheric and Oceanic Fluid Dynamics
What are tropopause polar vortices (TPVs)?
• Vortices that occur north and
away from jet stream
• Based on tropopause
• Cold core
Vortices defined by closed contours of a
materially conserved field such as PV
 Changes in strength equivalent to
changes in fluid properties within
closed contours
Disturbances wave-like along jet stream
25 June 2007
16th Conference on Atmospheric and Oceanic Fluid Dynamics
Why do we care about TPVs?
• Formation and intensity changes
are not well understood
• Are often long-lived
 Can have lifetimes > 1 month
• Trigger surface cyclones, such as in
the image above
 Eventually drift into midlatitudes
and jet stream, impacting the weather
25 June 2007
16th Conference on Atmospheric and Oceanic Fluid Dynamics
Ertel Potential Vorticity (EPV)
25 June 2007
16th Conference on Atmospheric and Oceanic Fluid Dynamics
What EPV changes can we expect with a cloud?
Latent heating
25 June 2007
Heating rate
16th Conference on Atmospheric and Oceanic Fluid Dynamics
What EPV changes can we expect with a cloud?
Latent heating
25 June 2007
EPV changes
16th Conference on Atmospheric and Oceanic Fluid Dynamics
What EPV changes can we expect with a cloud?
Radiation
25 June 2007
Heating rate
16th Conference on Atmospheric and Oceanic Fluid Dynamics
What EPV changes can we expect with a cloud?
Latent heating
25 June 2007
EPV changes
16th Conference on Atmospheric and Oceanic Fluid Dynamics
What EPV changes can we expect with a cloud?
Radiation + Latent
heating
25 June 2007
Net EPV changes
(radiation > latent heating)
16th Conference on Atmospheric and Oceanic Fluid Dynamics
What EPV changes can we expect with a cloud?
Radiation + Latent
heating
25 June 2007
Net EPV changes
(radiation < latent heating)
16th Conference on Atmospheric and Oceanic Fluid Dynamics
November 2005 TPV: Observations
GFS analysis tropopause pressure
Coral Harbour, NT sounding
21 November 2005 at 00 UTC
25 June 2007
16th Conference on Atmospheric and Oceanic Fluid Dynamics
November 2005 TPV: Observations
GFS analysis tropopause pressure
Coral Harbour, NT sounding
22 November 2005 at 00 UTC
25 June 2007
16th Conference on Atmospheric and Oceanic Fluid Dynamics
November 2005 TPV
GFS Tropopause  Analysis
WRF (V. 2.1.2) simulations:
• X = 30 km, Nz = 31
• 5-class microphysics, RRTM longwave
radiation
• GFS initial conditions, boundaries
updated every 3 hours
25 June 2007
16th Conference on Atmospheric and Oceanic Fluid Dynamics
November 2005 TPV
GFS Tropopause  Analysis
WRF (V. 2.1.2) simulations:
• X = 30 km, Nz = 31
• 5-class microphysics, RRTM longwave
radiation
• GFS initial conditions, boundaries
updated every 3 hours
25 June 2007
16th Conference on Atmospheric and Oceanic Fluid Dynamics
November 2005 TPV: Strengthening
PV Budget: Time mean vertical profiles for Siberia segment
All EPV components
25 June 2007
Diabatic components
16th Conference on Atmospheric and Oceanic Fluid Dynamics
November 2005 TPV: Strengthening
PV Budget
Time-height: Diabatic components
25 June 2007
Diabatic components
16th Conference on Atmospheric and Oceanic Fluid Dynamics
November 2005 TPV: Strengthening
PV Budget
Time-height: Radiation and cloud
25 June 2007
Diabatic components
16th Conference on Atmospheric and Oceanic Fluid Dynamics
November 2005 TPV: Strengthening
PV Budget
Time-height: Latent heat + Radiation
25 June 2007
Diabatic components
16th Conference on Atmospheric and Oceanic Fluid Dynamics
November 2005 TPV: Weakening
PV Budget: Time mean vertical profiles for Hudson Bay segment
All EPV components
25 June 2007
Diabatic components
16th Conference on Atmospheric and Oceanic Fluid Dynamics
Summary
•TPV strengthening from cloud-top radiational cooling in November
2005 TPV
•TPV weakening processes not clear, but strengthening no longer
appears to occur when latent heating effects dominate the radiational
effects.
• Is radiation always the key driver? What dynamics control
weakening?
 Work is underway involving idealized experiments to isolate
the dynamics responsible for TPV intensity changes.
25 June 2007
16th Conference on Atmospheric and Oceanic Fluid Dynamics
25 June 2007
16th Conference on Atmospheric and Oceanic Fluid Dynamics
What can we expect from a cloud?
25 June 2007
16th Conference on Atmospheric and Oceanic Fluid Dynamics