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Interactions between the Madden-Julian Oscillation and the North Atlantic Oscillation. Hai Lin Meteorological Research Division, Environment Canada Acknowledgements: Gilbert Brunet, Jacques Derome BIRS Workshop, Banff, Alberta, April 29, 2009. Outlines. Observed MJO – NAO connection
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Interactions between the Madden-Julian Oscillation and the North Atlantic Oscillation Hai Lin Meteorological Research Division, Environment Canada Acknowledgements: Gilbert Brunet, Jacques Derome BIRS Workshop, Banff, Alberta, April 29, 2009
Outlines • Observed MJO – NAO connection • Intraseasonal variability in a dry GCM
NAO and MJO connection • NAO: dominant large scale pattern in the extratropics with significant influence on weather from eastern North America to Europe • MJO: dominant tropical intraseasonal mode, coupled with convections and variability in diabatic heating • One-way impact, or two-way interaction? • A possible mechanism for both the NAO and MJO
Data and methodology Definition of the NAO: 2nd REOF of monthly Z500 NAO index: projection of pentad Z500 anomaly onto this pattern Period: 1979-2003 Extended winter, November to April (36 pentads each winter)
Data and methodology Definition of the MJO: combined EOF of OLR, u200 and u850 in the band of 15°S – 15°N (Wheeler and Hendon, 2004) NAO index: RMM1 and RMM2 Period: 1979-2003 Extended winter, November to April (36 pentads)
Composites of tropical Precipitation rate. Winter half year November-April Xie and Arkin pentad data, 1979-2003
Pentads in MJO phases Extended winter from 1979 to 2004
Lagged probability of the NAO indexPositive: upper tercile; Negative: low tercile
Benefit to Canadian surface air temperature forecasting Lagged winter SAT anomaly in Canada
Extratropical influence Lagged regression of 200mb U to NAO index
U200 composites Extratropical influence Lagged regression of 200mb U to NAO index
Model and experiment • Primitive equation AGCM (Hall 2000). • T31, 10 levels • Time-independent forcing to maintain the winter climate (1969/70-98/99) all variabilities come from internal dynamics • No moisture equation, no interactive convection • 3660 days of integration
Model Result Zonal propagation 10S-10N Unfiltered data 20-100 day band-pass Stronger in eastern Hemisphere
Wavenumber-frequency spectra Equatorial velocity potential wavenumber 10S-10N average
Wavenumber-frequency spectra Equatorial U wavenumber 10S-10N average
EOF analysis of 20-100 day band-passed 250 hPa velocity potential TIV index:
Horizontal structure 250 hPa u’,v’,z’
Vertical structure Regression to Day +8
TIV in the dry model • Kelvin wave structure • Phase speed: ~15 m/s (slower than free Kelvin wave, similar to convective coupled Kelvin wave, but there is no convection)
What causes the TIV in the dry model? • 3-D mean flow instability (Frederiksen and Frederiksen 1997) • Tropical-extratropical interactions (all wave energy generated in the extratropics) Moisture and convection related mechanisms are excluded Possible mechanisms
Regression to TIV index Color: 250mb velocity potential Contour: 250mb streamfunction anomaly TIV index: In phase with PC2
Regression to TIV index Color: 250mb velocity potential Contour: 250mb streamfunction anomaly TIV index: In phase with PC2
Regression to TIV index Color: 250mb velocity potential Contour: 250mb streamfunction anomaly TIV index: In phase with PC2
Regression to TIV index Color: 250mb velocity potential Contour: 250mb streamfunction anomaly TIV index: In phase with PC2
Regression to TIV index Color: 250mb velocity potential Contour: 250mb streamfunction anomaly TIV index: In phase with PC2
Regression to TIV index Color: 250mb velocity potential Contour: 250mb streamfunction anomaly TIV index: In phase with PC2
Regression to TIV index Color: 250mb velocity potential Contour: 250mb streamfunction anomaly TIV index: In phase with PC2
Regression to TIV index Color: 250mb velocity potential Contour: 250mb streamfunction anomaly TIV index: In phase with PC2
Regression to TIV index Color: 250mb velocity potential Contour: 250mb streamfunction anomaly TIV index: In phase with PC2
Regression to TIV index Color: 250mb velocity potential Contour: 250mb streamfunction anomaly TIV index: In phase with PC2
Regression to TIV index Color: 250mb velocity potential Contour: 250mb streamfunction anomaly TIV index: In phase with PC2
Regression to TIV index Color: 250mb velocity potential Contour: 250mb streamfunction anomaly TIV index: In phase with PC2
Regression to TIV index Color: 250mb velocity potential Contour: 250mb streamfunction anomaly TIV index: In phase with PC2
Regression to TIV index Color: 250mb velocity potential Contour: 250mb streamfunction anomaly TIV index: In phase with PC2
Regression to TIV index Color: 250mb velocity potential Contour: 250mb streamfunction anomaly TIV index: In phase with PC2
Regression to TIV index Color: 250mb velocity potential Contour: 250mb streamfunction anomaly TIV index: In phase with PC2
Regression to TIV index Color: 250mb velocity potential Contour: 250mb streamfunction anomaly TIV index: In phase with PC2
ISO in a dry model 250 hPa PV’ and wave activity flux Linked to tropical eastward propagation in the eastern Hemisphere Global propagation of low-frequency wave activity
Response to subtropical forcing 30N,30W, 30days 30N,180, 30days 30N,30W, 10days
Summary • Two-way interaction between the MJO and the NAO • Increase of NAO amplitude 5~15 days after the MJO-related convection anomaly reaches western Pacific • Certain MJO phases are preceded by strong NAOs • TIV generated in a dry GCM • Tropical-extratropical interactions are likely responsible for the model TIV
Implication to the MJO • A possible mechanism for the MJO: triggering, initialization • Contribution of moisture and tropical convection: spatial structure, phase speed