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Relation between PDO and large-scale ocean circulation variations

Relation between PDO and large-scale ocean circulation variations. ChuanLi Jiang Earth & Space Research, US Gary Lagerloef Earth & Space Research, US Scott Springer Earth & Space Researc h, US. Motivation.

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Relation between PDO and large-scale ocean circulation variations

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  1. Relation between PDO and large-scale ocean circulation variations ChuanLi JiangEarth & Space Research, US Gary LagerloefEarth & Space Research, US Scott Springer Earth & Space Research, US

  2. Motivation • Goal: do the oceanic dynamics play a role in the initiation and evolution of the Pacific Decadal Oscillation (PDO) (Clement et al., 2009, J.Climate)? • Hypothesis: with atmospheric stochastic forcing being strengthened and moved southward (40o to 35oN), Ekman transport, vertical mixing, surface heat fluxes intensified, gyre circulation moves southward; • Question 1: what physical processes contribute to the decadal new gyre (SSH field) re-establishment? • Question 2: what physical processes contribute to the decadal surface temperature (SST field) variations?

  3. PDO SSH index: upper ocean heat content variations (Cummins et al., 2005 GRL.) • PDO SSH altimetry index: robust indicator of PDO variations; consistent with JISAO SSH index; • ECCO2index: agrees with altimetry; • ESM2M index : erroneous regime shift1997-1998

  4. Data & Method • Time period: 1993-2012; • Lag regressions of the PDO-related variables against the PDO SSH index from 2 year before PDO (-2 year) to PDO peak (0 year); • Variables: altimetry SSH, RenoldsSST (OI.v2), OSCAR satellite-derived ocean currents, OAFlux net heat fluxes, ECCO2 observational-model synthesisSSH (Stammer et al., 2002 EOS.), GFDL-ESM2M carbon/climatecoupled model (similar climate fidelity as CM2.1) SSH (Dunne et al., 2012 Jclimate.); • GFDL-ESM2M historical (1993-2005), rcp85 (2006-2012);

  5. Lag regressions of altimetry SSH vs. ECCO2

  6. Lag regressions of altimetry SSH vs. ESM2M

  7. Lag regressions of SSH, SST against PDO SSH index

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  12. Conclusions • 20yr altimetry PDO index: a robust PDO indicator; • GFDL-ESM2M regime shift near 1997-1998 issue; • Wind stress anomalies in the central north Pacific one to two years before the PDO mature state accounted for much of the SSH tendency: • Once SSH fields are re-established, surface net heat fluxes, zonal advection by geostrophic currents, meridionaladvection by Ekman currents appear to contribute to the PDO SST tendency:

  13. Future work • Role of the Rossby wave and the observed mixed layer depth in the PDO variations; • Role of the oceanic dynamics in ECCO2 in the initiation and evolution of the PDO? • Role of the oceanic physics in GFDL-ESM2M in the initiation and evolution of the PDO? What causes the erroneous regime shift near 1997-1998?

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