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Two Types of Baroclinic Life Cycles during the Southern Hemisphere summer

Two Types of Baroclinic Life Cycles during the Southern Hemisphere summer. Woosok Moon and Steven Feldstein. Earth and Environmental Systems Institute, The Pennsylvania State University, University Park, Pennsylvania, U.S.A. Presented at the MOCA-09 conference, Montreal, Canada, July 21, 2009.

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Two Types of Baroclinic Life Cycles during the Southern Hemisphere summer

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  1. Two Types of Baroclinic Life Cycles during the Southern Hemisphere summer Woosok Moon and Steven Feldstein Earth and Environmental Systems Institute, The Pennsylvania State University, University Park, Pennsylvania, U.S.A. Presented at the MOCA-09 conference, Montreal, Canada, July 21, 2009.

  2. Baroclinic Life Cycles Idealized Model Studies (zonally uniform basic flow, small amplitude, unstable normal mode, wave perturbation) Gall (1976), Simmons and Hoskins (1978, 1980), Branscome et al. (1989), Feldstein and Held (1991), Barnes and Young (1992), Thorncroft et al. (1993), Hartmann (2000), Kunz et al. (2007), Wittman et al. (2007) Observational Studies: Randel and Stanford (1985a,b) 3 consecutive SH summer seasons Data and Methodology: NCEP/NCAR Reanalysis Data 1980-2004, SH summer, composite life cycles (synoptic-scale eddy energy > 1 standard deviation)

  3. Composite Baroclinic Life Cycle (69 cases) Total eddy energy Synoptic-scale eddy energy Baroclinic conversion Barotropic conversion Local maximum

  4. Composite Baroclinic Life Cycle weak barotropic (WB) Life Cycle strong barotropic (SB) Life Cycle Total eddy energy Synoptic-scale eddy energy Baroclinic conversion Barotropic conversion Local maximum

  5. Composite 925-hPa U & dU/dy WB Life Cycle SB Life Cycle Strengthened Jet Weakened Jet Weakened dU/dy Strengthened dU/dy

  6. WB (weak barotropic) life cycle Faster baroclinic growth Larger maximum amplitude Weaker dU/dy Weaker dU/dz SB (strong barotropic) life cycle Slower baroclinic growth Smaller maximum amplitude Stronger dU/dy Stronger dU/dz Is the barotropic governor playing a role in the WB and SB life cycles? Do baroclinic life cycles in the atmosphere depend more strongly upon dU/dy than dU/dz?

  7. Composite Anomalous EP Fluxes WB Life Cycle Poleward EP flux Tropical Rossby wave source Jet deceleration Baroclinic growth Barotropic decay

  8. Composite Anomalous EP Fluxes SB Life Cycle equatorward EP flux Tropical Rossby wave sink Jet acceleration Baroclinic growth Barotropic decay

  9. Composite Anomalous Mass Streamfunction Meridional cells weakened Meridional cells strengthened WBLife Cycle SBLife Cycle Anomalous EP flux Anomalous MMC Anomalous dU/dy

  10. Composite Anomalous 825-hPa Baroclinicity WBLife Cycle Weak dU/dz (lag -2 days) SB Life Cycle Strong dU/dz (lag -2 days) Is there a dynamical constraint involving dU/dy & dU/dz? Anomalous dU/dz>0 at end of both life cycles: Self-maintaining (Robinson 2006)

  11. Mass Steamfunction (decay stage) Anomalous MMC restores baroclinicity

  12. Composite Anomalous Outgoing Longwave Radiation Enhanced tropical convection Weakened tropical convection WB Life Cycle SB Life Cycle

  13. Conclusions WB Life Cycle SB Life Cycle

  14. Composite Anomalous Zonal Available Potential Energy

  15. Composite 300-hPa transient EKE

  16. Questions What process accounts for the barotropic conversion maximum at the start of the baroclinic life cycle? 2. Is there a preferred zonal mean flow and eddy flux structure at the start of a baroclinic life cycle? Two types of life cycles Weak barotropic (WB); Stong barotropic (SB)

  17. Composite Baroclinic SB Life Cycle Total eddy energy Synoptic-scale eddy energy Baroclinic conversion Barotropic conversion Weak local maximum

  18. Baroclinic Life Cycles Baroclinic growth: ZAPE EAPE Barotropic decay: EKE ZEKE Idealized Model Studies (zonally uniform basic flow, small amplitude, unstable normal mode, wave perturbation) Gall (1976), Simmons and Hoskins (1978, 1980), Branscome et al. (1989), Feldstein and Held (1991), Barnes and Young (1992), Thorncroft et al. (1993), Hartmann (2000), Kunz et al. (2007), Wittman et al. (2007) Observational Studies: Randel and Stanford (1985a,b) 3 consecutive SH summer seasons Data and Methodology: NCEP/NCAR Reanalysis Data 1980-2004, SH summer, composite life cycles (synoptic-scale eddy energy > 1 standard deviation)

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