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The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology Nonlinear Rainfall Response to El Nino and Global Warming in the Indo-Pacific Christine Chung Scott Power Julie Arblaster Harun Rashid Greg Roff www.cawcr.gov.au Pacific-Australia Climate Change Science and Adaptation Planning Program (PACCSAP)
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The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology ACCESS AGCM experiments How do weak/moderate/strong El Nino SST anomalies affect rainfall over tropical Pacific? How does this behaviour change under global warming? To investigate: SST-forced ACCESS AGCM experiments (using HadGEM-r1 config) Used annually-repeating 1979-2009 climatological SSTs Created EN composite, added 1-4x EN to clim. SSTs (20yrs each run) Global warming pattern: CMIP3 MMEM ([2080-2099] – [1980-1999])
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The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology EN SST anomaly & GW pattern
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The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology 20C rainfall clim 1EN 2EN 3EN 4EN
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The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology Moisture budget – EN-driven anomalies Precip Dynamic Thermodynamic Evap Covariant Based on Seager et al (2010)
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The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology Moisture budget – GW driven anomalies Precip Dynamic Thermodynamic Evap Covariant
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The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology Changes in SPCZ/ITCZ structure
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Observations – weak & strong EN The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology climatology 'weak' EN 'strong' EN (1982/83 & 1997/98) ITCZ SPCZ
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The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology Comparing to observations
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Strong EN years (82/83 & 97/98) The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology Added residual SST pattern (82/83 & 97/98 average anomaly minus 3EN anomaly) 3EN + 0β β +0.3 β +0.6 β +1.0 β +1.3 β
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Strong EN years (82/83 & 97/98) The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
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Caveats/issues Results are sensitive to GW SST pattern Unclear how EN SST anomaly patterns will change under global warming Time evolution of EN events
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The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology Summary How do changes in El Nino SST anomalies affect rainfall over tropical Pacific? Nonlinear increase/decrease in rainfall ITCZ shifts equatorwards, SPCZ more zonal Max rainfall anomaly along ITCZ shifts eastwards change in amplitude and structure of EN SST anomalies essential to reproduce strong EN events of 1982/83 & 1997/98
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Summary How does this behaviour change under global warming? response to EN is enhanced impact of GW depends on strength of EN GW-driven rainfall increase shifts eastwards for strong EN response is sensitive to GW SST pattern The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology
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The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology Thank you www.cawcr.gov.au
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The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology clim 1LN 2LN 3LN 4LN La Nina runs
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The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology La Nina moisture budget
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Changes in ITCZ/SPCZ structure The Centre for Australian Weather and Climate Research A partnership between CSIRO and the Bureau of Meteorology ITCZ SPCZ
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