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 Cycle

Poleward EP flux

Jet deceleration

Tropical Rossby wave source

Baroclinic

growth

Barotropic decay

Composite Anomalous EP Fluxes Composite Anomalous EP Fluxes SBSB Life Cycle Life Cycle

equatorward 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 Cycle

Enhanced tropical convection Weakened tropical convection

ConclusionsConclusions

WB Life CycleWB Life CycleWB Life CycleWB Life Cycle

SB Life CycleSB Life CycleSB 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