1 / 20

Atmospheric response to North Pacific SST

Atmospheric response to North Pacific SST. The role of model resolution and synoptic SST variability. Frontal-scale Air-sea Interaction Workshop Boulder, CO, USA August 6, 2013. Guidi Zhou, Mojib Latif , Wonsun Park*, Richard Greatbatch.

darrin
Download Presentation

Atmospheric response to North Pacific SST

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. Atmospheric response to North Pacific SST The role of model resolution and synoptic SST variability Frontal-scale Air-sea Interaction Workshop Boulder, CO, USA August 6, 2013 Guidi Zhou, Mojib Latif, WonsunPark*, Richard Greatbatch GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany *presenting

  2. Outline • Background and motivation • Observed atmospheric response to re-emergent SST • AGCM response • Sensitivity to background SST and horizontal resolution

  3. Background and motivation • Extra-tropical SST experiences annual reemergence [Alexander et al. 1999…] • The atmosphere responds to extra-tropical SST anomalies [Czaja & Frankignoul1999, 2002…] • Response is small compare to Tropical response and internal atm. variability [Palmer & Sun 1985; Kushnir et al. 2002…] • But potentially persistent due to the large thermal inertia of the oceanic mixed layer [Kushnir et al. 2002…] • Transient eddies are crucial [Peng & Whitaker 1999…] • Oceanic fronts are important for anchoring the storm-track [Minobe et al. 2008; Taguchi et al. 2009…]

  4. Observed atmospheric link to reemergent SST anomalies • ERSST 80-year winter-mean data • Remove ENSO from NP SST using linear regression (PC1*) • Lagged regression of SST on PC1* (PC1* leads) • SST reemergence found in NP Regressed SST on NP SST PC1* (ENSO removed)

  5. Observed atmospheric link to reemergentSST anomalies • ERSLP 80-year winter-mean data • Remove ENSO from NP SST PC using linear regression (PC1*) • Lagged regression of SLP on PC1* (PC1* leads) • Significant links between SLP and PC1* of previous winters • Deepened Aleutian Low Regressed SLP on NP SST PC1* (ENSO removed)

  6. Observed atmospheric link to reemergentSST anomalies Regressed SST on NP SST PC1* (ENSO removed) Regressed SLP on NP SST PC1* (ENSO removed)

  7. AGCM response to NP SSTa Experimental setup Model: ECHAM5 Resolution: T213 (~0.56°) L31 Background SST: NOAA-OI-Daily SST (time-varying 1981-1990, to preserve the fronts) SST anomaly forcing: +/- lag-0 regression pattern in NP 4-month (NDJF) integrations Initialized Nov.1, +/- 10 winters each Mean (DJF) differences between +/- SSTa experiments studied

  8. AGCM response to NP SSTa SST anomaly (doubled) PDO-like anomaly pattern (K)

  9. The relative position of the SST anomaly with respect to the full SST Positive PDO-like SSTapattern would reduce the front Contour: winter-mean climatological SST (°C) Shading: PDO-like SSTa(°C)

  10. AGCM response to NP SSTa response characteristics Deepened Aleutian Low (hPa)

  11. AGCM response to NP SSTa response characteristics Upward heat fluxes reinforce the SSTain some regions (W/m2)

  12. AGCM response to NP SSTa response characteristics Zonally averaged over NP equiv. barotropic accelerated jet stream deep convection Geopotential height (m) U-velocity (m/s) Vertical velocity (Pa/s)

  13. AGCM response to NP SSTa eddy forcing Consider 40°N (over cold SSTa) conv. eddy vorticity flux upper div., surface conv. conv. eddy momentum flux div. eddy vorticity flux (1/s2) divergence (1/s) div. eddy zonal momentum flux (m/s2)

  14. AGCM response to NP SSTa T213 Response summary Diagnostics (over cold SSTa) Convergence of eddy vorticity flux is balanced by divergence in circulation, resulting in ascent at mid-levels and low-level convergence. The vortex stretching associated produces the surface low. Convergence of eddy momentum flux reinforces the jet. Consistent with Kushnir et al. 2002... Characteristics • Equivalent barotropic low • Upward heat flux reinforcing the SSTain some regions • Accelerated jet stream • Deep convection • Deep diabaticheating • Enhanced storm-track

  15. High vs. low resolutions T31- response T213- response Geopotential height (m) Geopotential height (m)

  16. Influence of synoptic SST variability Sea surface temperature (K) Snapshot,Jan 01, 1982. Fine spatial/temporal structures on T213 Synoptic SST variability only in NP ctrl, NP SSTa experiments Climatological state, Jan 01 Smoothed spatial/temporal structures on T213 ctrl, NP SSTa experiments

  17. Observed daily varying SST vs. climatological SST as background T213-climatological background SST T213-daily varying North Pacific background SST no significant response significant eddy-mediated response

  18. Summary • North Pacific atmosphere response to underlying SST anomalies in observations • This can be simulated only with higher resolution of AGCM, e.g. T213 • Temporal resolution is also important in this aspect • The response is eddy-mediated In order to obtain a realistic response to midlatitude SST anomalies one needs to resolve the synoptic SST variability. This requires employing sufficiently high horizontal resolution. Guidi Zhou gzhou@geomar.de

  19. Zonal mean SST gradient Zonal (120°E-160°W) mean

More Related