Analysis of the potential vorticity budget of a tropopause polar cyclone

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 13th Cyclone Workshop

2. Outline • Tropopause polar vortices (TPVs) • Ertel potential vorticity (EPV) • Tropopause maps • November 2005 TPV • PV budget of November 2005 TPV 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 13th Cyclone Workshop

4. Waves and vortices These vortices often drift into mid-latitudes, sometimes triggering surface cyclogenesis • 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 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 13th Cyclone Workshop

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7. Radiational cooling at cloud top Radiational heating at cloud base 13th Cyclone Workshop

8. Heating Profile EPV Changes 13th Cyclone Workshop

9. Heating Profile EPV Changes 13th Cyclone Workshop

10. 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) 13th Cyclone Workshop

11. November 2005 TPV GFS analysis tropopause pressure Coral Harbour, NT sounding 21 November 2005 at 00 UTC 13th Cyclone Workshop

12. November 2005 TPV GFS analysis tropopause pressure Coral Harbour, NT sounding 22 November 2005 at 00 UTC 13th Cyclone Workshop

13. November 2005 TPV GFS analysis tropopause pressure Coral Harbour, NT sounding 23 November 2005 at 00 UTC 13th Cyclone Workshop

14. November 2005 TPV GFS analysis tropopause pressure Coral Harbour, NT sounding 24 November 2005 at 00 UTC 13th Cyclone Workshop

15. November 2005 TPV WRF simulations: • Horizontal grid spacing 30 km, 31 vertical levels • 5-class microphysics, RRTM longwave radiation • GFS analysis and boundaries updated every three hours 13th Cyclone Workshop

16. Siberia Averages within 285 K closed contour 13th Cyclone Workshop

17. Siberia Averages within 285 K closed contour 13th Cyclone Workshop

18. Siberia Averages within 285 K closed contour 13th Cyclone Workshop

19. Hudson Bay Averages within 280 K closed contour 13th Cyclone Workshop

20. Hudson Bay Values at center of vortex 13th Cyclone Workshop

21. Diabatic components EPV terms Siberia 13th Cyclone Workshop

22. Hudson Bay Diabatic components EPV terms 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? 13th Cyclone Workshop

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