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, 2009.
Two Types of Baroclinic Life Cycles Two Types of Baroclinic Life Cycles during the Southern Hemisphere summerduring the Southern Hemisphere summer
Baroclinic Life CyclesBaroclinic Life Cycles
Idealized Model Studies (Idealized Model Studies (zonally uniform basic flow, small amplitude, zonally uniform basic flow, small amplitude, unstable normal mode, wave perturbationunstable normal mode, wave perturbation))Gall (1976), Simmons and Hoskins (1978, 1980), Branscome et al. (1989), Gall (1976), Simmons and Hoskins (1978, 1980), Branscome et al. (1989), Feldstein and Held (1991), Barnes and Young (1992), Thorncroft et al. (1993), Feldstein and Held (1991), Barnes and Young (1992), Thorncroft et al. (1993), Hartmann (2000), Kunz et al. (2007), Wittman et al. (2007)Hartmann (2000), Kunz et al. (2007), Wittman et al. (2007)
Observational Studies: Observational Studies: Randel and Stanford (1985a,b)Randel and Stanford (1985a,b)
3 consecutive SH summer seasons3 consecutive SH summer seasons
Data and Methodology: Data and Methodology: 1980-2004, SH summer, composite life cycles 1980-2004, SH summer, composite life cycles (synoptic-scale eddy energy > 1 standard deviation)(synoptic-scale eddy energy > 1 standard deviation)NCEP/NCAR Reanalysis Data
Composite Baroclinic Life Cycle (69 cases)Composite Baroclinic Life Cycle (69 cases)
Synoptic-scale eddy energy
Barotropic conversion
Baroclinic conversion
Local maximum
Total eddy energy
weak barotropic (WB) Life Cycleweak barotropic (WB) Life Cycle strong barotropic (SB) Life Cyclestrong barotropic (SB) Life Cycle
Synoptic-scale
eddy energy
Barotropic
conversion
Baroclinic
conversion
Total eddy energy
Composite Baroclinic Life CycleComposite Baroclinic Life Cycle
Local maximum
Composite 925-hPa U & dU/dyComposite 925-hPa U & dU/dy
WB Life Cycle SB Life Cycle
Weakened Jet
Weakened dU/dy Strengthened dU/dy
Strengthened
Jet
WB (weak barotropic) life cycleWB (weak barotropic) life cycle
Faster baroclinic growthFaster baroclinic growthLarger maximum amplitudeLarger maximum amplitudeWeaker dU/dyWeaker dU/dyWeaker dU/dzWeaker dU/dz
SB (strong barotropic) life cycle SB (strong barotropic) life cycle
Slower baroclinic growthSlower baroclinic growthSmaller maximum amplitudeSmaller maximum amplitudeStronger dU/dyStronger dU/dyStronger dU/dzStronger dU/dz
Is the Is the barotropic governorbarotropic governor playing a role playing a role in the WB and SB life cycles?in the WB and SB life cycles?
Do baroclinic life cycles in the atmosphere depend Do baroclinic life cycles in the atmosphere depend more strongly upon more strongly upon dU/dydU/dy than than dU/dzdU/dz??
Composite Anomalous EP Fluxes Composite Anomalous EP Fluxes WBWB Life Cycle Life CyclePoleward EP flux
Jet deceleration
Tropical Rossby wave source
Baroclinic
growth
Barotropic decay
Composite Anomalous EP Fluxes Composite Anomalous EP Fluxes SBSB Life Cycle Life Cycleequatorward EP flux
Jet acceleration
Tropical Rossby wave sink
Baroclinic
growth
Barotropic decay
Composite Anomalous Mass StreamfunctionComposite Anomalous Mass Streamfunction
Meridional cells weakened Meridional cells strengthened
WB Life Cycle SB Life Cycle
Anomalous EP flux Anomalous MMC Anomalous dU/dy
Composite Anomalous 825-hPa BaroclinicityComposite Anomalous 825-hPa Baroclinicity
WB Life Cycle
SB Life Cycle
Weak dU/dzWeak dU/dz(lag -2 days)(lag -2 days)
Strong dU/dzStrong dU/dz(lag -2 days)(lag -2 days)
Anomalous dU/dz>0 at end of both life cycles:Anomalous dU/dz>0 at end of both life cycles:Self-maintaining (Robinson 2006)Self-maintaining (Robinson 2006)
Is there a dynamical constraint involving dU/dy & dU/dz?Is there a dynamical constraint involving dU/dy & dU/dz?
Anomalous MMC restores baroclinicityAnomalous MMC restores baroclinicity
Mass Steamfunction (decay stage)Mass Steamfunction (decay stage)
Composite Anomalous Composite Anomalous Outgoing Longwave RadiationOutgoing Longwave Radiation
WB Life Cycle SB Life CycleEnhanced tropical convection Weakened tropical convection
ConclusionsConclusions
WB Life CycleWB Life Cycle
SB Life CycleSB Life Cycle
Composite Anomalous Zonal Available Composite Anomalous Zonal Available Potential EnergyPotential Energy
Composite 300-hPa transient EKEComposite 300-hPa transient EKE
QuestionsQuestions
1.1. What process accounts for the What process accounts for the barotropic conversion barotropic conversion maximummaximum at the start of the baroclinic life cycle? at the start of the baroclinic life cycle?
2. 2. Is there a preferred Is there a preferred zonal mean flowzonal mean flow and and eddy fluxeddy flux structurestructure at the start of a baroclinic life cycle? at the start of a baroclinic life cycle?
Two types of life cyclesTwo types of life cyclesWeak barotropic (WB); Stong barotropic (SBWeak barotropic (WB); Stong barotropic (SB))
Composite Baroclinic SB Life CycleComposite Baroclinic SB Life Cycle
Total eddy energy
Synoptic-scale eddy energy
Baroclinic conversion
Barotropic conversion
Weak local maximum
Baroclinic growth: ZAPE EAPE Baroclinic growth: ZAPE EAPE Barotropic decay: EKE ZEKEBarotropic decay: EKE ZEKE
Baroclinic Life CyclesBaroclinic Life Cycles
Idealized Model Studies (Idealized Model Studies (zonally uniform basic flow, small amplitude, zonally uniform basic flow, small amplitude, unstable normal mode, wave perturbationunstable normal mode, wave perturbation))Gall (1976), Simmons and Hoskins (1978, 1980), Branscome et al. (1989), Gall (1976), Simmons and Hoskins (1978, 1980), Branscome et al. (1989), Feldstein and Held (1991), Barnes and Young (1992), Thorncroft et al. (1993), Feldstein and Held (1991), Barnes and Young (1992), Thorncroft et al. (1993), Hartmann (2000), Kunz et al. (2007), Wittman et al. (2007)Hartmann (2000), Kunz et al. (2007), Wittman et al. (2007)
Observational Studies: Observational Studies: Randel and Stanford (1985a,b)Randel and Stanford (1985a,b)
3 consecutive SH summer seasons3 consecutive SH summer seasons
Data and Methodology: Data and Methodology: 1980-2004, SH summer, composite life cycles 1980-2004, SH summer, composite life cycles (synoptic-scale eddy energy > 1 standard deviation)(synoptic-scale eddy energy > 1 standard deviation)NCEP/NCAR Reanalysis Data