The Madden-Julian Oscillation and Extremes in North American Precipitation

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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) - PowerPoint PPT Presentation

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The Madden-Julian Oscillation andExtremes in North American PrecipitationAdam Stepanek, Tom Murphree, Chuck WashDept of MeteorologyNaval Postgraduate School

22nd Pacific Climate Workshop 28 March 2006

1Overview of Madden-Julian Oscillations (MJOs) major and complex disturbances of the global tropical atmosphere-ocean systempropagating intraseasonal (~ 1-2 months) oscillationsusually start in tropical Indian - W Pacific regionhave largest amplitude in tropical Indian - Pacific regionpropagate E-ward through the tropicsmay propagate around globe, especially as UL disturbanceperiod 30-60 days 45 dayszonal wave length Earths circumferenceoccur throughout the yearmay have large impacts on global tropics and extratropicshave impacts on midlatitude climate strong atmosphere-ocean coupling makes them difficult to analyze and model 2

Evidence of MJOsSea Level Pressure, Equator and 180E, May Oct 1979Figure from R. Madden, 31 Aug 200545 days3Evidence of MJOsTemperature, Upper Ocean, Equator and 155W, Aug 1991 Jul 1992

45 daysT 125 m

T 150 m4MJO Structure: Indian Ocean and Western Pacific, Phases 1-8

convective anomalysubsidence anomalyconvectivecomponentsubsidencecomponent123458765 = positive heating anomaly = energy propagation through wave trainModeled Tropospheric Response to Western Tropical PacificPositive Heating Anomaly in Northern WinterMJOs and Teleconnections

HHHLL = dry air advection

= moist air advection6

MJOs and TeleconnectionsFigure from: Higgins and Mo, J Clim, 1997Relationships Between Propagating Tropical Positive Convection Anomaly and North Pacific North American Circulation and Precipitation Anomalies7Z 200 Anomalies, Dec 1996 Jan 1997MJOs and Teleconnections

During Dec 96 - Jan 97:Weak La Nina conditions in tropical PacificIntense MJO activity in Indian Ocean western tropical PacificAnomalously heavy precipitation and flooding in N CA, OR, WAAnomalously low precipitation in SW USExtratropical wave train similar to expected for MJO convection intropical E IO W Pacific

Other examples of MJO impacts on west coast precipitation?Jan 92, Feb 93, Jan 95, OctNov 03, Dec 04 Jan 05, Dec 05 - Jan 06

8Importance of the MJO forNorth Pacific - North American (NPNA) ClimateMJO 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.9Teleconnections Between Tropical Eastern Hemisphere andNorth Pacific - North AmericaFrom Schwing, Murphree, and Green, 2002. The Northern Oscillation Index: A New Climate Index for the Northeast Pacific. Progress in Oceanography, 53, 115-139.

Correlation of annual mean sea level pressure at 35N, 135W withsea level pressure globally10Motivations 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 events11DataNCEP/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 variables12Methods

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.


Z200 AnomalyWave train from east Asia to NPNAMJO ConvectionMJO Subsidence

Precip Rate AnomalyWet in PNW and BCComposites for: Phase 3, All Amplitudes, ONDJFM, andAll Background States14NPNA 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. Composites for: All Amplitudes, ONDJFM, and all Background States, by Phase Phase 6Phase 8Phase 3

15NPNA 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. ONDJFMONDJFM

Composites for: Phase 3, All Amplitudes, and all Background States, by Season 16EN or LN have large impacts on NPNA response to MJO, and vice versa. Cause: interference between convective and subsidence components.ZA200 Composites for: Phase 3, All Amplitudes, and ONDJFM, by Background StateAll States

El NinoLa Nina

Neutral175 Wettest Composites5 Driest CompositesPhase 2 / El Nio / ONDPhase 7 / La Nia / ONDPhase 2 / Neutral / ONDPhase 3 / La Nia / JFMPhase 6 / Neutral / ONDPhase 4 / Neutral / JFMPhase 1 / El Nio / JFMPhase 7 / La Nia / JFMPhase 7 / El Nio / JFMPhase 8 / Neutral / JFMMJO and Background Factors for 5 Wettest and 5 Driest Compsites for California 18

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.

Wet in CADry in CA

MJO-Related Composite Circulation and Precip Anomalies for Wet and Dry Conditions in CA19Favorable / Unfavorable Conditions for MJO-AssociatedAnomalously Wet Conditions in CAFavorableUnfavorable1. Early or late phases of the MJO 2. OND or JFM3. El Nio or neutral background state 4. Wave train from Asia with anomalouslow north and west of CA5. Southwest to northeast tilt to the anomalous low off CA 1. La Nia background state2. Middle phases of the MJOFavorable / Unfavorable Conditions for MJO-AssociatedAnomalously Dry Conditions in CAFavorableUnfavorable1. Middle or late phases of the MJO 2. JFM3. La Nia background state4. Anomalous high over northeastern Pacific1. Early phases of the MJO 2. El Nino background stateFavorable and Unfavorable Factors for Wet and Dry Conditions in California Corresponding results for PNW, BC, and AK regions (not shown)20ConclusionsThere 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).