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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)

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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 andExtremes in North American Precipitation

slide2

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
slide3

45 days

Evidence of MJOs

Sea Level Pressure, Equator and 180E, May – Oct 1979

Figure from R. Madden, 31 Aug 2005

slide4

T 125 m

T 150 m

45 days

Evidence of MJOs

Temperature, Upper Ocean, Equator and 155W, Aug 1991 – Jul 1992

slide5

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

slide6

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

slide7

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

slide8

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
slide9

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.
slide10

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.

slide11

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
slide12

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
slide13

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.
slide14

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

slide15

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.

slide16

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.

slide17

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.

slide19

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.

slide20

Favorable and Unfavorable Factors for Wet and Dry Conditions in California

Corresponding results for PNW, BC, and AK regions (not shown)

slide21

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).