NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

On the predictability of the winter NAO:

lagged influence of autumn Eurasian snow and Arctic sea-ice

J. García-Serrano, C. Frankignoul, G. Gastineau

LOCEAN-IPSL, UPMC, Paris, France

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

Extended Maximum Covariance Analysis (EMCA)

our approach relies on capturing time-evolving predictor in covariance with the winter NAO, but

holding its spatial pattern; by means of introducing different time-lags in the MCA analysis

Polo et al. & García-Serrano et al. (2008, J.CLIM)

ERA-Interim (SD): 1979-2012

NOAA/NSIDC (SCE): 1966-2012

NOAA-CIRES 20CR (SD): 1966-2010

common period 1979-2010 (October)

SNOW week 1

SNOW week 2

SNOW week 3

SNOW week 4

SNOW week 5

SLP

(DJF)

X = ( NLAGw * nsSNOW ) x nyr

Y = nsSLP x nyr

COV = ( X * Yt ) / nyr-1

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

EMCA-SCE (oct)

scf=51.2% ruv=0.77

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

upward-propagating wave activity (stratospheric mechanism)

at 100hPa

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

transient-eddy feedback (tropospheric mechanism)

at 200hPa

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

upward-propagating wave activity

(stratospheric mechanism)

at 100hPa

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

transient-eddy feedback

(tropospheric mechanism)

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

transient-eddy feedback

(tropospheric mechanism)

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

Summary:

• Both, October Eurasian SCE and autumn (Sep-Oct-Nov) Arctic SIE expansion coefficients have a correlation of ~0.7-0.8 with winter Euro-Atlantic SLP variability.

• October Eurasian SCE leads to changes in the Siberian High, which further lead to enhanced/reduced vertical wave activity over eastern Eurasia, affecting the stratospheric polar vortex over the North Pacific sector.

• Arctic SIC triggers a wavetrain crossing Eurasia in November that (i) impacts vertical wave activity over both the North Pacific and northern European sectors, hence affecting the polar vortex; and (ii) induces transient-eddy feedback over the eastern North Atlantic basin helping to maintain and amplify the tropospheric anomaly.

• The winter NAO and EMCA-SCE (October Eurasian SCE) show significant negative correlations over the Kara-Barents Seas in autumn, i.e. SIC reduction over the eastern Arctic, in agreement with MCA-SIC patterns.

• There is a negative feedback in SIC over the eastern Arctic between autumn (negative anomalies - reduction) and winter (positive anomalies - increase), which is mediated by the NAO.

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

SIC (oct) SIC (nov)

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

Summary:

• Both, October Eurasian SCE and autumn (Sep-Oct-Nov) Arctic SIE expansion coefficients have a correlation of ~0.7-0.8 with winter Euro-Atlantic SLP variability.

• October Eurasian SCE leads to changes in the Siberian High, which further lead to enhanced/reduced vertical wave activity over eastern Eurasia, affecting the stratospheric polar vortex over the North Pacific sector.

• Arctic SIC triggers a wavetrain crossing Eurasia in November that (i) impacts vertical wave activity over both the North Pacific and northern European sectors, hence affecting the polar vortex; and (ii) induces transient-eddy feedback over the eastern North Atlantic basin helping to maintain and amplify the tropospheric anomaly.

• The winter NAO and EMCA-SCE (October Eurasian SCE) show significant negative correlations over the Kara-Barents Seas in autumn, i.e. SIC reduction over the eastern Arctic, in agreement with MCA-SIC patterns.

• There is a negative feedback in SIC over the eastern Arctic between autumn (negative anomalies - reduction) and winter (positive anomalies - increase), which is mediated by the NAO.

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

Summary:

• Both, October Eurasian SCE and autumn (Sep-Oct-Nov) Arctic SIE expansion coefficients have a correlation of ~0.7-0.8 with winter Euro-Atlantic SLP variability.

• October Eurasian SCE leads to changes in the Siberian High, which further lead to enhanced/reduced vertical wave activity over eastern Eurasia, affecting the stratospheric polar vortex over the North Pacific sector.

• Arctic SIC triggers a wavetrain crossing Eurasia in November that (i) impacts vertical wave activity over both the North Pacific and northern European sectors, hence affecting the polar vortex; and (ii) induces transient-eddy feedback over the eastern North Atlantic basin helping to maintain and amplify the tropospheric anomaly.

• The winter NAO and EMCA-SCE (October Eurasian SCE) show significant negative correlations over the Kara-Barents Seas in autumn, i.e. SIC reduction over the eastern Arctic, in agreement with MCA-SIC patterns.

• There is a negative feedback in SIC over the eastern Arctic between autumn (negative anomalies - reduction) and winter (positive anomalies - increase), which is mediated by the NAO.

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

On the predictability of the winter NAO:

lagged influence of autumn Eurasian snow and Arctic sea-ice

EXTRA SLIDES

Honda et al. (2009, GRL)

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

NACLIM CT1 annual meeting, Trieste, 1-2/10/2013

The research leading to these results has received funding from the European Union 7th Framework Programme (FP7 2007-2013), under grant agreement n.308299

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