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: 2 nd REOF of monthly Z500 NAO index: projection of pentad Z500 anomaly onto this pattern Period: 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: Extended winter, November to April (36 pentads)

Composites of tropical Precipitation rate. Winter half year November-April Xie and Arkin pentad data,

Pentads in MJO phases Extended winter from 1979 to 2004 Phase Number of pentads Mean amplitude

Lagged composites of the NAO index Phase Lag −5 − Lag −4 − Lag −3 −0.29 Lag − Lag −1 Lag 0 −0.41 Lag −0.25−0.35 Lag −0.31−0.33−0.29 Lag −0.35−0.41 Lag +4 −0.35−0.31 Lag +5 −0.27

Lagged composites of the NAO index Phase Lag −5 − Lag −4 − Lag −3 −0.29 Lag − Lag −1 Lag 0 −0.41 Lag −0.25−0.35 Lag −0.31−0.33−0.29 Lag −0.35−0.41 Lag +4 −0.35−0.31 Lag +5 −0.27

Lagged probability of the NAO index Positive: upper tercile; Negative: low tercile Phase Lag −5 −35%−40%+49% Lag −4 +52%+46% Lag −3 −40%+46% Lag −2 +50% Lag −1 Lag 0 +45%−42% Lag %+45%−46% Lag %+50%+42%−41% −42% Lag %−41%−48% Lag +4 −39%−48% Lag +5 −41%

Tropical influence

Wave activity flux and 200mb streamfunction anomaly

Benefit to Canadian surface air temperature forecasting Lagged winter SAT anomaly in Canada

Lagged regression of 200mb U to NAO index Extratropical influence

U200 composites

Lagged regression of 200mb U to NAO index Extratropical influence U200 composites

Tropical intraseasonal variability (TIV) in a dry GCM

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

Unfiltered data day band-pass Zonal propagation 10S-10N Model Result Stronger in eastern Hemisphere

Wavenumber-frequency spectra Equatorial velocity potential 10S-10N average wavenumber

Wavenumber-frequency spectra Equatorial U 10S-10N average wavenumber

EOF analysis of 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

Tropica-extratropical interactions in the dry GCM

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 Linked to tropical eastward propagation in the eastern Hemisphere  Global propagation of low-frequency wave activity 250 hPa PV’ and wave activity flux

Response to subtropical forcing 30N,30W, 10days 30N,30W, 30days30N,180, 30days

Response to subtropical forcing

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

Source of LFV in extratropics From mean flow From high-frequency transients

250 hPa kinetic energy conversion from mean flow E vector C

250 hPa Z tendency caused by vorticity flux convergence of high-frequency transients

Vertical structure Regression to Day +8