Woosok Moon and Steven Feldstein Earth and Environmental Systems Institute, The Pennsylvania State University, University Park, Pennsylvania, U.S.A. Presented at the AMS AOFD conference, Stowe, Vermont, June 8, Two Types of Baroclinic Life Cycles during the Southern Hemisphere summer

Baroclinic Life Cycles 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 3 consecutive SH summer seasons Data and Methodology: NCEP/NCAR Reanalysis Data , SH summer, composite life cycles , SH summer, composite life cycles (synoptic-scale eddy energy > 1 standard deviation)

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

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

Composite 925-hPa U & dU/dy WB Life CycleSB Life Cycle Weakened Jet Weakened dU/dy Strengthened dU/dy Strengthened Jet

WB (weak barotropic) life cycle 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 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?

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

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

Composite Anomalous Mass Streamfunction Meridional cells weakenedMeridional cells strengthened WB Life CycleSB Life Cycle Anomalous EP fluxAnomalous MMCAnomalous dU/dy

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

Anomalous MMC restores baroclinicity Mass Steamfunction (decay stage)

Composite Anomalous Composite Anomalous Outgoing Longwave Radiation WB Life Cycle SB Life Cycle Enhanced tropical convectionWeakened tropical convection

Conclusions WB Life Cycle SB Life Cycle

Composite Anomalous Zonal Available Potential Energy Potential Energy

Composite 300-hPa transient EKE

Questions Questions 1.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 )

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

Baroclinic growth: ZAPE EAPE Barotropic decay: EKE ZEKE Baroclinic Life Cycles 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 3 consecutive SH summer seasons Data and Methodology: NCEP/NCAR Reanalysis Data , SH summer, composite life cycles , SH summer, composite life cycles (synoptic-scale eddy energy > 1 standard deviation)