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Jian Lu

COLA. The Position of the Midlatitude Storm Track and Eddy-Driven Jet. Jian Lu. Acknowledgment: Dargan W. Frierson (UW) Gang Chen (Cornell) Ed Gerber (NYU) Seok-Woo Son (McGill). Apr. 12, 10, SAC.

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Jian Lu

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  1. COLA The Position of the Midlatitude Storm Track and Eddy-Driven Jet Jian Lu Acknowledgment: Dargan W. Frierson (UW) Gang Chen (Cornell) Ed Gerber (NYU) Seok-Woo Son (McGill) Apr. 12, 10, SAC

  2. COLA Mission: Physical mechanisms of anthropogenic forcing and impacts on hydrological cycle. Previously: • Lu, Vecchi, Reichler, 2007: Weakening and expansion of the Hadley cell under global warming • Frierson, Lu, Chen, 2007: Verify Held (2000) against Held and Hou (1980) theory on the width of the Hadley cell. • Lu, Frierson, Chen 2008; Chen, Lu and Frierson, 2008: Propose complementary hypotheses of static stability and phase speed (tropopause) for the shift of the jet stream/storm track and expansion of the HC during DJF season. • Lu, Deser, Reichler, 2009: Attribution to the anthropogenic cause of the widening of the Tropics since late 1950s

  3. Weakening of the tropical circulation (Vecchi and Soden, 07) Expansion of the Hadley cell ==> expansion of the dry zone (Lu et al. 07). Circulation impacts on the pattern of hydroclimate

  4. COLA ensemble mean δ(P-E) in future climate P-E edges of the dry zone mm/day

  5. Poleward shift of the storm track and eddy-driven wind ==> intensified precipitation at mid-to-hi latitudes. Yin (2005)

  6. Zonal mean wind response to global warming Lorenz and DeWeaver (2007)

  7. Goals • Make sense of these large scale circulation response from first principle reasoning • Hadley cell extent • Storm track position/Eddy-Driven Surface Westerlies (EDSW) • To gain some predictive power thereof.

  8. Scaling in an aqua-planet world Full model (PCCM3) [Caballero and Langen, 2005] Idealized gray model • Aquaplanet (no ice) • NCAR CCM2 dynamical core • NCAR CCM3.6 physics • Aquaplanet (no ice) • Spectral dynamic core • Gray radiation (no H2O and cloud radiative feedbacks) • Simplified Monin-Obukhov surface flux scheme • K-profile boundary layer scheme • simplified Betts-Miller convection scheme

  9. SST boundary forcing 55°C -40°C

  10. Lat of eddy-driven westerly wind (EDSW) as a function of Tm and ∆T

  11. Non-Acceleration: (Caricature of Held and Hoskins 1985, DelSole 2001) • Tendency for thedFy/dyto compensation for-dFz/dz • Direction of influence:-FzFy

  12. ξ lat lat Lat of max EDSW lat of max EKE

  13. SST • θy is unknowable, barring a closure theory for mid-lat moist storm track dynamics. • Nonlinear Eddy adjustment determines θy (Robinson, 2000, 2006) • Theory for the stratification ∆V • Juckes (2000) • Frierson (2006; 2008) • Pick a reference (Tm=20, ∆T=40) state and compute –fθy /∆V with θyfixed at the value of the reference state.

  14. Procedure of scaling :INPUT INPUT: dθ/dy from a reference state (Tm=20; ΔT=40) Juckes (2000) SST Static Stability Δv Baroclinicity ξ= f dθ/dy[Δv]-1 (used to parameterize Fz) OUTPUT: Shift in max ξ (indicates the direction of the shift of the EDJ)

  15. Decipher Juckes theory for static stability ∆v : Tropopause Δzθe L=Δzθe /Δ yθes Δyθes equator pole

  16. δ(ξp-ξe)/ξm v shift of EDSW 100% frac change of δξ gives rise to 7 deg lat shift in storm track

  17. Same slope!!

  18. Remaining questions and on-going work • Challenges in understanding the circulation change on sectoral scale (collaborating with Gerber, Chen, and Frierson) • Apply the Fluctuation-Dissipation Theorem to the leading modes of variability of the mid-latitude atmospheric circulation and their climate projection. • [Leith, 1975; Gerber et al., 2008; Chen and Plumb, 2009; Ring and Plumb, 2009; Kidston and Gerber, 2010; Gritsun and Branstator, 2007] • Understand the role of ocean circulation change in the climate response to global warming, using partial coupling technique. (special thanks to Jim Hurrell)

  19. Experiments to unravel the role of ocean dynamics

  20. Effect of oceanic feedback Full Disabled ocean feedback Effect of ocean feedback Replication 27

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