Transcript of The Madden-Julian Oscillation and Extremes in North American Precipitation Adam Stepanek, Tom...
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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
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Overview of Madden-Julian Oscillations (MJOs) 1.major and
complex disturbances of the global tropical atmosphere- ocean
system 2.propagating intraseasonal (~ 1-2 months) oscillations
3.usually start in tropical Indian - W Pacific region 4.have
largest amplitude in tropical Indian - Pacific region 5.propagate
E-ward through the tropics 6.may propagate around globe, especially
as UL disturbance 7.period 30-60 days 45 days 8.zonal wave length
Earths circumference 9.occur throughout the year 10.may have large
impacts on global tropics and extratropics 11.have impacts on
midlatitude climate 12.strong atmosphere-ocean coupling makes them
difficult to analyze and model
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Evidence of MJOs Sea Level Pressure, Equator and 180E, May Oct
1979 Figure from R. Madden, 31 Aug 2005 45 days
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Evidence of MJOs Temperature, Upper Ocean, Equator and 155W,
Aug 1991 Jul 1992 45 days T 125 m T 150 m
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MJO Structure: Indian Ocean and Western Pacific, Phases 1-8
convective anomalysubsidence anomaly convective component
subsidence component 1 2 3 4 5 8 7 6
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= positive heating anomaly = energy propagation through wave
train Modeled Tropospheric Response to Western Tropical Pacific
Positive Heating Anomaly in Northern Winter MJOs and
Teleconnections H H H L L = dry air advection = moist air
advection
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MJOs and Teleconnections Figure from:
http://www.cpc.ncep.noaa.gov/products/intraseasonal/intraseasonal_faq.html#what
cf. Higgins and Mo, J Clim, 1997 Relationships Between Propagating
Tropical Positive Convection Anomaly and North Pacific North
American Circulation and Precipitation Anomalies
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Z 200 Anomalies, Dec 1996 Jan 1997 MJOs and Teleconnections
During Dec 96 - Jan 97: 1.Weak La Nina conditions in tropical
Pacific 2.Intense MJO activity in Indian Ocean western tropical
Pacific 3.Anomalously heavy precipitation and flooding in N CA, OR,
WA 4.Anomalously low precipitation in SW US 5.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, OctNov 03, Dec 04 Jan 05, Dec 05 - Jan
06
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Importance of the MJO for North Pacific - North American (NPNA)
Climate 1.MJO impacts NA climate on intraseasonal scale.
2.Cumulative and indirect effects of MJO may affect NA climate on
longer time scales. 3.EN and LN are not the only explanation for
NPNA anomalies. 4.MJO has significant interactions with longer
period tropical climate variations (e.g., ENLN, IOZM, Asian monsoon
variations). 5.EN and LN have large event-to-event variability that
may be explained by interactions with other climate variations.
6.MJO may be a good dynamical proxy for longer period tropical
climate variations more MJO samples to analyze.
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Teleconnections Between Tropical Eastern Hemisphere and North
Pacific - North America From 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 with sea
level pressure globally
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Motivations and Objectives 1. 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). 2. 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
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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
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Methods No band pass filtering, unlike prior studies
Constructed all possible 7-day lagged composites according to four
factors: 1. MJO phase (1-8) 2. MJO amplitude (low, medium, high) 3.
MJO season of occurrence (OND, JFM, ONDJFM) 4. 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.
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Z200 Anomaly Wave train from east Asia to NPNA MJO Convection
MJO Subsidence Precip Rate Anomaly Wet in PNW and BC Composites
for: Phase 3, All Amplitudes, ONDJFM, and All Background
States
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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. Composites for: All Amplitudes, ONDJFM, and all
Background States, by Phase Phase 6 Phase 8 Phase 3
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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. OND JFM ONDJFM Composites for: Phase 3, All
Amplitudes, and all Background States, by Season
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EN 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 State All States El NinoLa Nina Neutral
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5 Wettest Composites5 Driest Composites Phase 2 / El Nio /
ONDPhase 7 / La Nia / OND Phase 2 / Neutral / ONDPhase 3 / La Nia /
JFM Phase 6 / Neutral / ONDPhase 4 / Neutral / JFM Phase 1 / El Nio
/ JFMPhase 7 / La Nia / JFM Phase 7 / El Nio / JFMPhase 8 / Neutral
/ JFM MJO and Background Factors for 5 Wettest and 5 Driest
Compsites for California
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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 CA Dry in CA MJO-Related
Composite Circulation and Precip Anomalies for Wet and Dry
Conditions in CA
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Favorable / Unfavorable Conditions for MJO-Associated
Anomalously Wet Conditions in CA FavorableUnfavorable 1. Early or
late phases of the MJO 2. OND or JFM 3. El Nio or neutral
background state 4. Wave train from Asia with anomalous low north
and west of CA 5. Southwest to northeast tilt to the anomalous low
off CA 1. La Nia background state 2. Middle phases of the MJO
Favorable / Unfavorable Conditions for MJO-Associated Anomalously
Dry Conditions in CA FavorableUnfavorable 1. Middle or late phases
of the MJO 2. JFM 3. La Nia background state 4. Anomalous high over
northeastern Pacific 1. Early phases of the MJO 2. El Nino
background state Favorable and Unfavorable Factors for Wet and Dry
Conditions in California Corresponding results for PNW, BC, and AK
regions (not shown)
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Conclusions 1.There are understandable patterns in MJO impacts
on NPNA. 2.EN and LN are not the only explanation for NPNA
anomalies. 3.MJO interactions with EN and LN are important for
NPNA. 4.Both the convective and the subsidence components of MJO,
EN, and LN must be accounted for. 5.NPNA response to MJO is more
persistent if MJO amplitude is high --- perhaps because MJO
amplitude and phase speed are inversely related. 6.Event-to-event
variability of EN and LN may be explained in part by interactions
of EN and LN with MJO, and vice versa. 7.Analyses and modeling of
climate variations needs to account for multiple concurrent
variations (e.g., concurrent EN and MJO).