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The Madden-Julian Oscillation and Extremes in North American Precipitation

Adam Stepanek, Tom Murphree, Chuck Wash Dept of Meteorology Naval Postgraduate School 22nd Pacific Climate Workshop 28 March 2006. The Madden-Julian Oscillation and Extremes in North American Precipitation. Overview of Madden-Julian Oscillations (MJOs)

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The Madden-Julian Oscillation and Extremes in North American Precipitation

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  1. Adam Stepanek, Tom Murphree, Chuck Wash Dept of Meteorology Naval Postgraduate School 22nd Pacific Climate Workshop 28 March 2006 The Madden-Julian Oscillation andExtremes in North American Precipitation

  2. Overview of Madden-Julian Oscillations (MJOs) • major and complex disturbances of the global tropical atmosphere-ocean system • propagating intraseasonal (~ 1-2 months) oscillations • usually start in tropical Indian - W Pacific region • have largest amplitude in tropical Indian - Pacific region • propagate E-ward through the tropics • may propagate around globe, especially as UL disturbance • period 30-60 days  45 days • zonal wave length Earth’s circumference • occur throughout the year • may have large impacts on global tropics and extratropics • have impacts on midlatitude climate • strong atmosphere-ocean coupling makes them difficult to analyze and model

  3. 45 days Evidence of MJOs Sea Level Pressure, Equator and 180E, May – Oct 1979 Figure from R. Madden, 31 Aug 2005

  4. T 125 m T 150 m 45 days Evidence of MJOs Temperature, Upper Ocean, Equator and 155W, Aug 1991 – Jul 1992

  5. MJO Structure: Indian Ocean and Western Pacific, Phases 1-8 subsidence component 5 1 convective component 2 6 7 3 8 4 convective anomaly subsidence anomaly

  6. MJOs and Teleconnections H L L H H Modeled Tropospheric Response to Western Tropical Pacific Positive Heating Anomaly in Northern Winter = positive heating anomaly = energy propagation through wave train = dry air advection = moist air advection

  7. MJOs and Teleconnections Relationships Between Propagating Tropical Positive Convection Anomaly and North Pacific – North American Circulation and Precipitation Anomalies cf. Higgins and Mo, J Clim, 1997 Figure from: http://www.cpc.ncep.noaa.gov/products/intraseasonal/intraseasonal_faq.html#what

  8. MJOs and Teleconnections Z 200 Anomalies, Dec 1996 – Jan 1997 • During Dec 96 - Jan 97: • Weak La Nina conditions in tropical Pacific • Intense MJO activity in Indian Ocean – western tropical Pacific • Anomalously heavy precipitation and flooding in N CA, OR, WA • Anomalously low precipitation in SW US • Extratropical wave train similar to expected for MJO convection in • tropical E IO – W Pacific • Other examples of MJO impacts on west coast precipitation? • Jan 92, Feb 93, Jan 95, Oct–Nov 03, Dec 04 – Jan 05, Dec 05 - Jan 06

  9. Importance of the MJO for • North Pacific - North American (NPNA) Climate • MJO impacts NA climate on intraseasonal scale. • Cumulative and indirect effects of MJO may affect NA climate on longer time scales. • EN and LN are not the only explanation for NPNA anomalies. • MJO has significant interactions with longer period tropical climate variations (e.g., ENLN, IOZM, Asian monsoon variations). • EN and LN have large event-to-event variability that may be explained by interactions with other climate variations. • MJO may be a good dynamical proxy for longer period tropical climate variations  more MJO samples to analyze.

  10. Teleconnections Between Tropical Eastern Hemisphere and North Pacific - North America Correlation of annual mean sea level pressure at 35N, 135W with sea level pressure globally From Schwing, Murphree, and Green, 2002. The Northern Oscillation Index: A New Climate Index for the Northeast Pacific. Progress in Oceanography, 53, 115-139.

  11. Motivations and Objectives • Prior studies implicated MJO in positive and negative precipitation anomalies in western NA in fall-winter (e.g., Bond and Vecchi 2003, Jones 2000, Higgins and Mo 1997, Mo and Higgins 1998). • But many unresolved issues, including relevance to NPNA of: • a. MJO phase • b. MJO amplitude • b. subsidence component of MJO • c. season of MJO occurrence • d. concurrent EN or LN events

  12. Data • NCEP/NCAR reanalysis fields: • 200-hPa geopotential height anomaly (ZA200) • Outgoing longwave radiation anomalies (OLRA) • Precipitation rate anomaly (PRA) • MJO Index: • Real-time Multivariate MJO (RMM) Index (Wheeler and Hendon, MWR, 2004) • Based on tropical OLR, U850 winds and U200 winds • El Nino / La Nina (EN/LN) Index (Wolter and Timlin, 1993, 1998): • Multivariate ENSO Index (MEI) • Based on six tropical Pacific atmosphere and ocean variables

  13. Methods • No band pass filtering, unlike prior studies • Constructed all possible 7-day lagged composites according to four factors: • MJO phase (1-8) • MJO amplitude (low, medium, high) • MJO season of occurrence (OND, JFM, ONDJFM) • ENLN background state (EN, LN, or neutral) • From composites, identified MJO-related circulation and anomaly patterns that characterized positive and negative precipitation anomalies in four regions of western NA.

  14. Composites for: Phase 3, All Amplitudes, ONDJFM, and All Background States Wave train from east Asia to NPNA MJO Convection MJO Subsidence Precip Rate Anomaly Wet in PNW and BC Z200 Anomaly

  15. Composites for: All Amplitudes, ONDJFM, and all Background States, by Phase Phase 3 Phase 6 Phase 8 NPNA response to MJO is affected by MJO phase. Effects can be dramatic. Likely causes: shifts in convective and subsidence components leads to changes in interactions with east Asia - North Pacific jet.

  16. Composites for: Phase 3, All Amplitudes, and all Background States, by Season ONDJFM OND JFM NPNA response to MJO affected by season. Effects can be dramatic. Likely causes: seasonal changes in location of convection and subsidence, and in strength, location, shear of east Asia - North Pacific jet.

  17. ZA200 Composites for: Phase 3, All Amplitudes, and ONDJFM, by Background State All States El Nino La Nina Neutral EN or LN have large impacts on NPNA response to MJO, and vice versa. Cause: interference between convective and subsidence components.

  18. MJO and Background Factors for 5 Wettest and 5 Driest Compsites for California

  19. MJO-Related Composite Circulation and Precip Anomalies for Wet and Dry Conditions in CA Wet in CA Dry in CA EN and LN effects evident. But MJO effects evident in wave train from east Asia, and deviations of composites from EN and LN means. N-S dipole in western NA.

  20. Favorable and Unfavorable Factors for Wet and Dry Conditions in California Corresponding results for PNW, BC, and AK regions (not shown)

  21. Conclusions • There are understandable patterns in MJO impacts on NPNA. • EN and LN are not the only explanation for NPNA anomalies. • MJO interactions with EN and LN are important for NPNA. • Both the convective and the subsidence components of MJO, EN, and LN must be accounted for. • NPNA response to MJO is more persistent if MJO amplitude is high --- perhaps because MJO amplitude and phase speed are inversely related. • Event-to-event variability of EN and LN may be explained in part by interactions of EN and LN with MJO, and vice versa. • Analyses and modeling of climate variations needs to account for multiple concurrent variations (e.g., concurrent EN and MJO).

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