Christopher G Fletcher and Paul J Kushner Department of Physics, University of Toronto, Canada. [email protected] Linear interference effects

QuickTime™ and a decompressor

are needed to see this picture.Christopher G Fletcher and Paul J KushnerDepartment of Physics, University of Toronto, [email protected]

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


are needed to see this picture.



ENSO+

Trend

[Shin and Sardeshmukh 2010]


Motivation



[Cagnazzo and Manzini 2009][Garfinkel and Hartmann 2008]

[Bell et al. 2009]

ENSO+ NAM—

also:[Ineson and Scaife 2009]



TIO+ NAO+

[Annamalai et al. 2007][Hoerling et al. 2004]

[Bader and Latif 2005]

also:[Sanchez-Gomez et al. 2009]


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.


GFDL AM2.1 Experiments:

TIO TPO

TIP

Amplitude0.4 ~ 1.0

- N = 100- Independent ICs- Repeating Seas Cycle- JF response


OLR and Chi200hPa Response

TIO TPO

TIP






TIOTPOTIP

TIOTPOTIP

wavenumber-1

wavenumber-2


[∆Z]



TIO

TPO

TIP


[∆Z]



TIO

TPO

TIP

[Thompson and Wallace 2000]

NAM—

NAM+

NAM Pattern (+)

why?




TIO

TPOQuickTime™ and a

decompressorare needed to see this picture.



Z*(60N)




Eddy Meridional Heat Flux Response (mK s-1)

[∆Z] ~ [v*T*]





[v*T*] decomposition: TOTAL = EM + FL





[v*T*] decomposition: TOTAL = EM + FLEM = LIN + NONLIN




[v*T*] decomposition: TOTAL = EM + FLEM = LIN + NONLINLIN ~ wv_1 + wv_2



What happens to the NAM response when we perturb the climatological stationary wave?


Flatten the topography over:1. Tibet and northern Eurasia (NOTIBET)2. Rocky Mountains (NOROCK)



Standard Model NOTIBET case difference

500 hPa Geopotential Heights


[∆Z]

NOTIBET cases NOROCK case

TIOTPO TPO



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.


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



Winter 2009/10






Pattern of Tropical SST trends

[Shin and Sardeshmukh 2010]

[Barsugli et al. 2006]


∆Z*200hPa







TIO TPO

TIP



Control (unforced) climatologies: STD and NOTIBET


Control (unforced) climatologies: STD and NOTIBET






TIOTPOTIP

TIOTPOTIP

wavenumber-1

wavenumber-2


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?


Documents

Christopher G Fletcher and Paul J Kushner Department of Physics, University of Toronto, Canada. [email protected] Linear interference effects