ivana herceg buliĆ

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IVANA HERCEG BULIĆ ANDRIJA MOHOROVIČIĆ GEOPHYSICAL INSTITUTE, DEPARTMENT OF GEOPHYSICS, FACULTY OF SCIENCE, UNIVERSITY OF ZAGREB, ZAGREB, CROATIA FRED KUCHARSKI THE ABDUS SALAM INTERNATIONAL CENTRE FOR THEORETICAL PHYSICS, EARTH SYSTEM PHYSICS SECTION, TRIESTE, ITALY DELAYED ENSO IMPACT ON SPRING PRECPITATION OVER NORTH ATLANTIC/EUROPEAN REGION EMS&ECAM 2011 12 – 16 September 2011; Berlin, Germany

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DELAYED ENSO IMPACT ON SPRING PRECPITATION OVER NORTH ATLANTIC/EUROPEAN REGION. IVANA HERCEG BULIĆ ANDRIJA MOHOROVIČIĆ GEOPHYSICAL INSTITUTE, DEPARTMENT OF GEOPHYSICS, FACULTY OF SCIENCE, UNIVERSITY OF ZAGREB, ZAGREB, CROATIA FRED KUCHARSKI - PowerPoint PPT Presentation

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Page 1: IVANA HERCEG BULIĆ

IVANA HERCEG BULIĆANDRIJA MOHOROVIČIĆ GEOPHYSICAL INSTITUTE, DEPARTMENT OF

GEOPHYSICS, FACULTY OF SCIENCE, UNIVERSITY OF ZAGREB, ZAGREB, CROATIA

 

FRED KUCHARSKITHE ABDUS SALAM INTERNATIONAL CENTRE FOR THEORETICAL

PHYSICS, EARTH SYSTEM PHYSICS SECTION, TRIESTE, ITALY

DELAYED ENSO IMPACT ON SPRING PRECPITATION OVER NORTH ATLANTIC/EUROPEAN

REGION

EMS&ECAM 2011 12 – 16 September 2011; Berlin, Germany

Page 2: IVANA HERCEG BULIĆ

Introduction

SST anomalies in tropical oceans – strong generator of climate variability on Earth

SST anomalies in tropical Pacific associated with ENSO – affect both tropical and extratropical atmosphere

Impact on midlatitudes – tropical extratropical-teleconnections – Rossby wave propagation

ENSO impact on Pacific-North American (PNA) region – widely investigated and well documented

ENSO impact on North Atlantic/European region (NAE) – controversial

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Herceg Bulić and Kucharski: Delayed ENSO impact on spring precipitation over North Atlantic/European region

Page 3: IVANA HERCEG BULIĆ

Introduction

Winter ENSO forcing:

Herceg Bulić and Branković (ClimDyn 2007); Herceg Bulić, Branković and Kucharski (ClimDyn 2011):

Symmetrical ENSO signal in the winter climate anomalies over the PNA region (PNA pattern) in Z200 anomalies as well as in other atmospheric variables (precipitation, temperature, mslp …)Weak but detectable winter ENSO signal over the NAE region (in line with some previous observational as well modelling studies; e.g. Fraedrich, Tellus 1994; Brönnimann, RevGeophys 2007)

• Generally, El Niño ⇒ cyclonic type of weather La Niña ⇒ anticyclonic type of weather

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Herceg Bulić and Kucharski: Delayed ENSO impact on spring precipitation over North Atlantic/European region

ENSO signal in warmer climate conditions: PNA – weakeningNAE – strengthening

(e.g. Müller & Roeckner, ClimDyn 2008; Herceg Bulić et al., ClimDyn 2011)

Page 4: IVANA HERCEG BULIĆ

Motivation4

Herceg Bulić and Kucharski: Delayed ENSO impact on spring precipitation over North Atlantic/European region

Besides concurrent (JFM → JFM) atmospheric response to the ENSO forcing, time-delayed ENSO effect on NAE region has been also reported by some authors (e.g. Rodó et.al. ClimDyn 1997; Kiladis and Dias JClim 1989; van Oldenborg et.al. IntJClimatol 2000)

According to some findings, spring precipitation anomaly in the NAE region may be even stronger than that in winter – possible time-lagged teleconnection between winter tropical Pacific SST conditions and NAE region

Delayed ENSO impact on seasonal precipitation anomalies cannot be explained solely by Rossby wave propagation theory → a lack of dynamical interpretation underpinning the time delayed tropical – extratropical teleconnections

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Experimental design5

Herceg Bulić and Kucharski: Delayed ENSO impact on spring precipitation over North Atlantic/European region

Time period: 1901 – 2002

Observational data:

• Precipitation: Climatic Research Unit (CRU) gridded monthly dataset (0.5°×0.5°)

• Sea-level pressure: HadSLP re-analysis (5°×5°); provided by Hadley Centre, UK

• Sea-surface temperature: NOAA_ERSST_V2 data (provided by NOAA/OAR/ESRL PSD, USA)

– Sea-ice climatology (provided by Hadley Centre, UK)

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Experimental design6

Herceg Bulić and Kucharski: Delayed ENSO impact on spring precipitation over North Atlantic/European region

Modeled data: ensembles of numerical simulations performed by ICTP AGCM (SPEEDY; T30L8)

1. CTRL experiment: ensemble of 20 ICTP AGCM numerical simulations forced with observed global monthly SST anomalies

2. MIX experiment: ensemble of 10 integrations performed with ICTP AGCM coupled with a passive slab ocean layer in the North Atlantic and SST forcing acting in the

Indo-Pacific tropical basin

3. MIX_winter_ENSO experiment: same as the MIX experiment, but with SST forcing in the Indo-Pacific basin acting from October until March

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Results – correlation PC1(CRU PREC)NAE → global JFM SSTA

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Herceg Bulić and Kucharski: Delayed ENSO impact on spring precipitation over North Atlantic/European region

Focus on AMJ seasonal

precipitation

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Results - correlation PC1(AMJ PREC) → JFM SSTA (tropical Pacific)

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Herceg Bulić and Kucharski: Delayed ENSO impact on spring precipitation over North Atlantic/European region

Time-lagged correlations: suggestion of time delayed (JFM → AMJ) impact of tropical Pacific

But, they may be associated also with contemporaneous (AMJ → AMJ) influence as a consequence of seasonal persistence of SST conditions in tropical Pacific

Page 9: IVANA HERCEG BULIĆ

Results - correlation PC1(AMJ PREC) → AMJ SSTA (tropical Pacific)

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Herceg Bulić and Kucharski: Delayed ENSO impact on spring precipitation over North Atlantic/European region

Concurrent (AMJ-AMJ) correlations considerably weaker than the time-lagged (JFM-AMJ)

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Results - correlation PC1(AMJ PREC) → JFM SSTA (tropical Pacific) – MIX_winter_ENSO experiment

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Herceg Bulić and Kucharski: Delayed ENSO impact on spring precipitation over North Atlantic/European region

MIX_winter_ENSO experiment:ENSO forcing restricted to the cold part of year (Oct – Mar)

Page 11: IVANA HERCEG BULIĆ

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Herceg Bulić and Kucharski: Delayed ENSO impact on spring precipitation over North Atlantic/European region

Results – precipitation warm and cold ENSO composites

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Results – Physical mechanism of time delayed ENSO impact on precipitation in NAE region

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Herceg Bulić and Kucharski: Delayed ENSO impact on spring precipitation over North Atlantic/European region

CRU and SPEEDY precipitation data have demonstrated time delayed ENSO impact on precipitation in the NAE region

Results obtained by MIX_winter_ENSO experiment exclude seasonal persistence of ENSO as a potential explanation

Rossby wave propagation mechanism can not explain winter-spring teleconnection

Some intermediary physical mechanism is expected to be involved

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Results – a tentative diagram of physical mechanism explaining time delayed ENSO impact

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Herceg Bulić and Kucharski: Delayed ENSO impact on spring precipitation over North Atlantic/European region

Atmospheric bridge (Lau and Nath, JClim 1996)

Trop PacSSTJFM

TropAtmosphereJFM

MidlatatmosphereJFM

Midlat AtlSSTAMJ

MidlatatmosphereAMJ

Page 14: IVANA HERCEG BULIĆ

Results – physical mechanism14

Herceg Bulić and Kucharski: Delayed ENSO impact on spring precipitation over North Atlantic/European region

Page 15: IVANA HERCEG BULIĆ

Conclusions – Winter ENSO impact on spring precipitation in the NAE region

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Herceg Bulić and Kucharski: Delayed ENSO impact on spring precipitation over North Atlantic/European region

Observed as well as modelled data showed significant time-lagged NAE precipitation response to the winter ENSO forcing

JFM warm (cold) ENSO events are associated with wetter (drier) AMJ precipitation conditions in the central part of the NAE region

Results obtained by SPEEDY simulations with the ENSO forcing restricted to the cold part of year underlie those findings and exclude ENSO seasonal persistence as a major mechanism causing delayed atmospheric response

Physical mechanism undrepinning time-delayed atmospheric response to the ENSO forcing includes Rossby wave-train which constitutes atmospheric-bridge between the tropical Pacific and North Atlantic. Induced mid–latitude Atlantic SST anomalies interact with the overlaying atmosphere altering westerly winds and onshore moisture advection. As a result, downstream sea-level pressure pattern is modulated likewise the precipitation