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Investigating the Connection Between PDO and Large-Scale Ocean Circulation Variations

This research explores the relationship between ocean dynamics and the Pacific Decadal Oscillation (PDO). The study hypothesizes that changes in atmospheric forcing and intensified oceanic processes influence the initiation and evolution of the PDO. Key questions focus on the physical processes contributing to decadal gyre re-establishment and surface temperature variations. The analysis spans 1993-2012, utilizing lag regressions of various oceanic indicators. Findings reveal robust PDO indicators and suggest wind stress anomalies impact SSH tendencies preceding PDO peaks. Future work aims to further elucidate ocean dynamics' roles in PDO variations.

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Investigating the Connection 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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