Interactions between the Madden-Julian Oscillation and the North Atlantic Oscillation

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Interactions between the Madden-Julian Oscillation and the North Atlantic Oscillation. Hai Lin, Gilbert Brunet Meteorological Research Division, Environment Canada Jacques Derome McGill University TTISS, Monterey, September 14, 2009. Outlines. Observed MJO – NAO connection - PowerPoint PPT Presentation

Text of Interactions between the Madden-Julian Oscillation and the North Atlantic Oscillation

  • Interactions between the Madden-Julian Oscillation and the North Atlantic OscillationHai Lin, Gilbert BrunetMeteorological Research Division, Environment Canada

    Jacques DeromeMcGill University

    TTISS, Monterey, September 14, 2009

  • OutlinesObserved MJO NAO connection Lin et al. 2009 (J. Climate)

    Intraseasonal variability in a dry GCM Lin et al. 2007 (J. Atmos. Sci.)

  • NAO and MJO connectionNAO: dominant large scale pattern in the extratropics with significant influence on weather from eastern North America to EuropeMJO: dominant tropical intraseasonal mode, coupled with convections and variability in diabatic heatingOne-way impact, or two-way interaction?A possible mechanism for both the NAO and MJO

  • Data and methodologyDefinition of the NAO: 2nd REOF of monthly Z500NAO index: projection of pentad Z500 anomaly onto this patternPeriod: 1979-2003Extended winter, November to April (36 pentads each winter)

  • Data and methodologyDefinition of the MJO: combined EOF of OLR, u200 and u850 in the band of 15S 15N (Wheeler and Hendon, 2004)

    NAO index: RMM1 and RMM2Period: 1979-2003Extended winter, November to April (36 pentads)

  • Composites of tropicalPrecipitation rate.

    Winter half yearNovember-April

    Xie and Arkin pentad data, 1979-2003

  • Pentads in MJO phasesExtended winter from 1979 to 2004

  • Lagged composites of the NAO index

  • Lagged composites of the NAO index

  • Lagged probability of the NAO indexPositive: upper tercile; Negative: low tercile

  • Tropical influence

  • Wave activity flux and 200mb streamfunction anomaly

  • Lagged regression of 200mb U to NAO indexExtratropical influence

  • Lagged regression of 200mb U to NAO indexExtratropical influence U200 composites

  • Tropical intraseasonal variability (TIV) in a dry GCM

  • Model and experimentPrimitive equation AGCM (Hall 2000).T31, 10 levelsTime-independent forcing to maintain the winter climate (1969/70-98/99) all variabilities come from internal dynamicsNo moisture equation, no interactive convection3660 days of integration

  • Unfiltered data20-100 day band-passZonal propagation10S-10NModel ResultStronger in eastern Hemisphere

  • TIV in the dry model

    Kelvin wave structurePhase 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 excludedPossible mechanisms

  • ISO in a dry modelLinked to tropical eastward propagation in the eastern Hemisphere Global propagation of low-frequency wave activity250 hPa PV and wave activity flux

  • SummaryTwo-way interaction between the MJO and the NAOIncrease of NAO amplitude 5~15 days after the MJO-related convection anomaly reaches western PacificCertain MJO phases are preceded by strong NAOsTIV generated in a dry GCMTropical-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

  • To assess the contribution of moisture and convections to LFV, especially the MJO.Does tropical intraseasonal variability (TIV) exist in a dry model? Global view of the intraseasonal variability.Implication to the MJOSource of LFV in extratropics:*From mean flow*From high-frequency transients