1 / 34

North Pacific Decadal Variability: Role of Ocean-Atmosphere Coupling

North Pacific Decadal Variability: Role of Ocean-Atmosphere Coupling. Lixin Wu and Zhengyu Liu Center For Climatic Research University of Wisconsin-Madison. Collaborators Dr. R. Jacob, Dr. R. Gallimore, Ms. D. Lee and Ms. Y. Zhong. Paleoclimate Observation:

durantj
Download Presentation

North Pacific Decadal Variability: Role of Ocean-Atmosphere Coupling

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. North Pacific Decadal Variability:Role of Ocean-Atmosphere Coupling Lixin Wu and Zhengyu Liu Center For Climatic Research University of Wisconsin-Madison Collaborators Dr. R. Jacob, Dr. R. Gallimore, Ms. D. Lee and Ms. Y. Zhong

  2. Paleoclimate Observation: Tree Ring Reconstruction Southwest Drought Northern Plains Drought D. Stahle and E. Cook

  3. “Modes” of Pacific Decadal Variability Tropical Pacific Mode North Pacific Mode Eastern North Pacific Mode

  4. Fundamentals of Pacific Decadal Variability • Two Key issues: • Where does the memory reside? • (2) What is role of the O/A feedback?

  5. Feedback ?? Mid-Lat Memory OK? Extra-Trop Feedback OK Tropics Memory ?? Potential Mechanisms Variability Process Mechanism Teleconnection ??

  6. Coupled Modeling Surgery • Grand Geophysical Laboratory: Coupled Climate model FOAM_1.5 (Fast Ocean Atmosphere Model, Jacob,1997) AGCM: CCM2 Dynamics/CCM3 Physics (R15) OGCM: POP-like (2.8o*1.4o*24-level) No flux adjustment • Modeling Surgery: Partial-Coupling: constrain A/O coupling in selected regions by selected variables Partial-Blocking: Constrain regional oceanic teleconnection

  7. Model NPM and ENPM Z500 SST ENPM NPM Wu and Liu, 2003

  8. North Pacific Decadal Variability No ENSO No coupling

  9. SST SST Z500 SST Z500 NO ENSO NO A/O Coupling ENPM ENPM NPM NPM

  10. Modeling Evidence Two Distinctive Decadal Modes in the North Pacific: • NPM: Coupled ocean-atmosphere mode • ENPM: Stochastic Mode under the influence of tropics in conjunction with oceanic Rossby wave propagation ( Spatial resonance)

  11. Midlatitute SST-Atmosphere Feedback • Observational Evidence? Target Unclear • Modeling simulation? Diverse and confusing

  12. Previous Model Simulations

  13. Observational evidence inferred from lagged correlation of SLP, surface wind and Kuroshio Extension SST Model Model Ctrl NCEP Atm. lead Ocn. lead Atm. Lead Ocn. lead • Atmospheric forcing of ocean, dominant; • Atmospheric response to ocean, with season Liu and Wu, 2004

  14. Statistic EstimationFrankignoul et al., 1998 A(t) =  T(t) + N(t) A: atmosphere, T: SST, N: atmospheric noise Since <T(t-), N(t)> = 0 < T(t-), A(t)> =  < T(t-), T(t)> + < T(t-), N(t)>  = < A(t), T(t-)>/<T(t),T(t-)>

  15. FOAM Statistic Estimation of Atmospheric Response NCEP Surface wind 850 hPa  H H 250 hPa  H H

  16. AMIP (Fixed SST forcing) SST anomaly

  17. Wet Dry AMIP Response Z850 Z250 H H

  18. Coupled Ensemble Experiment Initial value approach Initial mixed T’>0 (Nov.1st) Atmosphere Ocean MLTA Ensemble simulations (Dec. mean)

  19. Wet Dry Fully Coupled Response Z850 Z250 H H

  20. Thermally Coupled Ensemble Response Dry Wet Z850 Z250 H H

  21. ? Geopotential Height Temperature Diabatic Heating AMIP ? FCE TCE

  22. Why weak heat flux but stronger warm-ridge response in Fully Coupled Ensemble ?

  23. Wet Fixed Heat Flux Response Z850 Z250 L L

  24. Modeling Evidence The atmospheric response depends not only on SST but also on flux boundary condition. The correct response can be attained only in fully coupled O/A system with a natural combination of SST and heat flux.

  25. Why weak heat flux in Fully Coupled Ensemble ? v’Ty SST Heat Budget Heat flux Fully Coupled Conv Thermally Coupled

  26. SST Propagation in FCE Slow oceanic process Fast Atmospheric Bridge

  27. ATMOSPHERE Model Climatology + Prescribed wind stress Anomaly Heat and Moisture Flux Wind stress OCEAN

  28. Coupled ocean-atmosphere response WARM COLD COLD WARM LOW LOW HIGH HIGH LOW LOW

  29. Summary • Potential positive SST-atmosphere feedback over the mid-latitude western Pacific • The atmospheric response “appears” to be driven by both the SST and heat flux forcing; the former favors a warm-high response, while the latter a warm-low response • The fully coupled model generates, perhaps, the most correct atmospheric response, because it generates the correct combination of SST and heat flux forcing. • The atmospheric response is best described in the coupled system as a part of a least damped coupled mode

  30. Thank you

  31. SST Mean Flow Storm track Heat flux Warm-ridge response Eddy vorticity forcing Hypothesis 1: Flux-SST Forcing Hypothesis • The SST forcing forces a warm-ridge response, while the heat flux forcing forces a warm-low response. The combination drives the coupled response. (heat flux is the cause !) SST • Problem: Why the SST and heat flux act independently?

  32. Hypothesis 2: Eddy-Feedback Forcing Hypothesis SST Heat flux Mean Flow Storm track Warm-ridge response Eddy vorticity forcing • A warm SST distorts the storm track northward and generate a warm-ridge response due to the eddy-vorticity forcing. The atmospheric easterly wind reduces the surface heat flux loss. The stronger the response, the weaker the flux (heat flux is the result !) • Problem: Why a stronger SST generates a stronger • warm-ridge response?

  33. Hypothesis 3: Coupled Mode Hypothesis • The atmospheric response is best described in the coupled • system as a part of a least damped coupled mode • Problem: • What is the role of coupling, on eddy or on flow?

More Related