christopher g fletcher and paul j kushner department of physics, university of toronto, canada
DESCRIPTION
Linear interference effects on tropical-extratropical teleconnections. Christopher G Fletcher and Paul J Kushner Department of Physics, University of Toronto, Canada. [email protected]. EGU General Assembly 2010, Vienna, Austria. Motivation. ENSO+. Trend. - PowerPoint PPT PresentationTRANSCRIPT
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Linear interference effects on tropical-extratropical teleconnectionsLinear interference effects on tropical-extratropical teleconnections
EGU General Assembly 2010, Vienna, Austria.
EGU General Assembly 2010, Vienna, Austria. 2
Motivation
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ENSO+
Trend
[Shin and Sardeshmukh 2010]
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Motivation
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[Cagnazzo and Manzini 2009][Garfinkel and Hartmann 2008]
[Bell et al. 2009]
ENSO+ NAM—
also:[Ineson and Scaife 2009]
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TIO+ NAO+
[Annamalai et al. 2007][Hoerling et al. 2004]
[Bader and Latif 2005]
also:[Sanchez-Gomez et al. 2009]
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Main findings
• We compare the extratropical NAM response to tropical Pacific and Indian Ocean SST warming.
• Both forcings produce Rossby wave trains but the NAM responses are opposite-signed.
• The NAM response is determined by linear interference between the wave response and the climatological stationary wave
• Perturbing the climatological stationary wave results in very different NAM responses.
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GFDL AM2.1 Experiments:
TIO TPO
TIP
Amplitude0.4 ~ 1.0
- N = 100- Independent ICs- Repeating Seas Cycle- JF response
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OLR and Chi200hPa Response
TIO TPO
TIP
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TIOTPOTIP
TIOTPOTIP
wavenumber-1
wavenumber-2
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[∆Z]
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TIO
TPO
TIP
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[∆Z]
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TIO
TPO
TIP
[Thompson and Wallace 2000]
NAM—
NAM+
NAM Pattern (+)
why?
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TIO
TPOQuickTime™ and a
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Z*(60N)
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Eddy Meridional Heat Flux Response (mK s-1)
[∆Z] ~ [v*T*]
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Eddy Meridional Heat Flux Response (mK s-1)
[v*T*] decomposition: TOTAL = EM + FL
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Eddy Meridional Heat Flux Response (mK s-1)
[v*T*] decomposition: TOTAL = EM + FLEM = LIN + NONLIN
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[v*T*] decomposition: TOTAL = EM + FLEM = LIN + NONLINLIN ~ wv_1 + wv_2
Eddy Meridional Heat Flux Response (mK s-1)
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What happens to the NAM response when we perturb the climatological stationary wave?
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Flatten the topography over:1. Tibet and northern Eurasia (NOTIBET)2. Rocky Mountains (NOROCK)
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Standard Model NOTIBET case difference
500 hPa Geopotential Heights
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[∆Z]
NOTIBET cases NOROCK case
TIOTPO TPO
Eddy Meridional Heat Flux Response (mK s-1)
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Concluding Remarks
Linear interference determines the sign and amplitude of the zonal mean (NAM) response to tropical SST forcing
The phase and amplitude of the climatological wave are critical for NAM teleconnections; example of flattening Eurasia/Rockies.
Indian Ocean is a “sweet-spot” for forcing NAM responses: implications for future SST trends?
See Karen Smith’s poster XY103 today, which explores midlatitude forcings.
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Reference
Fletcher, C. G., and P. J. Kushner, 2010: The role of linear interference in the Annular Mode response to tropical SST forcing, J. Climate, in review.
Preprint available at: www.atmosp.physics.utoronto.ca/people/cgf
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Winter 2009/10
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Pattern of Tropical SST trends
[Shin and Sardeshmukh 2010]
[Barsugli et al. 2006]
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∆Z*200hPa
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TIO TPO
TIP
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Control (unforced) climatologies: STD and NOTIBET
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Control (unforced) climatologies: STD and NOTIBET
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TIOTPOTIP
TIOTPOTIP
wavenumber-1
wavenumber-2
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The Problem
• The model is forced by two tropical warmings: one strong (TPO), the other weaker (TIO).
• Both forcings produce poleward propagating wave trains that scale roughly with forcing amplitude.
• But the NAM responses are of opposite sign and similar in strength. Why?
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