Presentation is loading. Please wait.

Presentation is loading. Please wait.

Atmospheric response to North Pacific SST The role of model resolution and synoptic SST variability Guidi Zhou, Mojib Latif, Wonsun Park*, Richard Greatbatch.

Similar presentations


Presentation on theme: "Atmospheric response to North Pacific SST The role of model resolution and synoptic SST variability Guidi Zhou, Mojib Latif, Wonsun Park*, Richard Greatbatch."— Presentation transcript:

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

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

3  Extra-tropical SST experiences annual reemergence [Alexander et al. 1999…]  The atmosphere responds to extra-tropical SST anomalies [Czaja & Frankignoul 1999, 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…] Background and motivation

4 Observed atmospheric link to reemergent SST anomalies Regressed SST on NP SST PC1* (ENSO removed)  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

5 Observed atmospheric link to reemergent SST anomalies Regressed SLP on NP SST PC1* (ENSO removed)  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

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

7 AGCM response to NP SSTa  Model: ECHAM5  Resolution: T213 (~0.56°) L31  Background SST: NOAA-OI-Daily SST (time-varying , 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 Experimental setup

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 Contour: winter-mean climatological SST (°C) Shading: PDO-like SSTa (°C) Positive PDO-like SSTa pattern would reduce the front

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

11 AGCM response to NP SSTa response characteristics (W/m 2 ) Upward heat fluxes reinforce the SSTa in some regions

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

13 AGCM response to NP SSTa eddy forcing div. eddy vorticity flux (1/s 2 ) conv. eddy vorticity flux divergence (1/s)div. eddy zonal momentum flux (m/s 2 ) upper div., surface conv.conv. eddy momentum flux Consider 40°N (over cold SSTa)

14 AGCM response to NP SSTa Characteristics Diagnostics (over cold SSTa) T213 Response summary  Equivalent barotropic low  Upward heat flux reinforcing the SSTa in some regions  Accelerated jet stream  Deep convection  Deep diabatic heating  Enhanced storm-track  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

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

16 Influence of synoptic SST variability Snapshot, Jan 01, 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 Sea surface temperature (K)

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

18  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 Summary 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

19

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


Download ppt "Atmospheric response to North Pacific SST The role of model resolution and synoptic SST variability Guidi Zhou, Mojib Latif, Wonsun Park*, Richard Greatbatch."

Similar presentations


Ads by Google