1. Christopher G Fletcher and Paul J Kushner Department of Physics, University of Toronto, Canada. chris.fletcher@utoronto.ca Linear interference effects on tropical- extratropical teleconnections EGU General Assembly 2010, Vienna, Austria.

2. 2 Motivation ENSO+ Trend [Shin and Sardeshmukh 2010]

3. EGU General Assembly 2010, Vienna, Austria. 3 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]

4. EGU General Assembly 2010, Vienna, Austria. 4 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.

5. EGU General Assembly 2010, Vienna, Austria. 5 GFDL AM2.1 Experiments: TIOTPO TIP Amplitude 0.4 ~ 1.0 - N = 100 - Independent ICs - Repeating Seas Cycle - JF response

6. EGU General Assembly 2010, Vienna, Austria. 6 OLR and Chi 200hPa Response TIOTPO TIP

7. EGU General Assembly 2010, Vienna, Austria. 7 TIOTPOTIP TIOTPOTIP wavenumber-1 wavenumber-2

8. EGU General Assembly 2010, Vienna, Austria. 8 [ ∆ Z] TIO TPO TIP

9. EGU General Assembly 2010, Vienna, Austria. 9 [ ∆ Z] TIO TPO TIP [Thompson and Wallace 2000] NAM — NAM + NAM Pattern (+) why?

10. EGU General Assembly 2010, Vienna, Austria. 10 TIO TPO Z*(60N)

11. EGU General Assembly 2010, Vienna, Austria. 11 Eddy Meridional Heat Flux Response (mK s -1 ) [ ∆ Z] ~ [v*T*]

12. EGU General Assembly 2010, Vienna, Austria. 12 Eddy Meridional Heat Flux Response (mK s -1 ) [v*T*] decomposition:TOTAL = EM + FL

13. EGU General Assembly 2010, Vienna, Austria. 13 Eddy Meridional Heat Flux Response (mK s -1 ) [v*T*] decomposition:TOTAL = EM + FL EM = LIN + NONLIN

14. EGU General Assembly 2010, Vienna, Austria. 14 [v*T*] decomposition:TOTAL = EM + FL EM = LIN + NONLIN LIN ~ wv_1 + wv_2 Eddy Meridional Heat Flux Response (mK s -1 )

15. EGU General Assembly 2010, Vienna, Austria. 15 What happens to the NAM response when we perturb the climatological stationary wave?

16. EGU General Assembly 2010, Vienna, Austria. 16 Flatten the topography over: 1.Tibet and northern Eurasia (NOTIBET) 2.Rocky Mountains (NOROCK) Standard Model NOTIBET case difference 500 hPa Geopotential Heights

17. EGU General Assembly 2010, Vienna, Austria. 17 [ ∆ Z] NOTIBET casesNOROCK case TIO TPO Eddy Meridional Heat Flux Response (mK s -1 )

18. EGU General Assembly 2010, Vienna, Austria. 18 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.

19. EGU General Assembly 2010, Vienna, Austria. 19 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

20. EGU General Assembly 2010, Vienna, Austria. 20

21. EGU General Assembly 2010, Vienna, Austria. 21 Winter 2009/10

22. EGU General Assembly 2010, Vienna, Austria. 22 Pattern of Tropical SST trends [Shin and Sardeshmukh 2010] [Barsugli et al. 2006]

23. EGU General Assembly 2010, Vienna, Austria. 23 ∆Z*200hPa TIO TPO TIP

24. EGU General Assembly 2010, Vienna, Austria. 24

25. EGU General Assembly 2010, Vienna, Austria. 25 Control (unforced) climatologies: STD and NOTIBET

26. EGU General Assembly 2010, Vienna, Austria. 26 Control (unforced) climatologies: STD and NOTIBET

27. EGU General Assembly 2010, Vienna, Austria. 27 TIOTPOTIP TIOTPOTIP wavenumber-1 wavenumber-2

28. EGU General Assembly 2010, Vienna, Austria. 28 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?

29. EGU General Assembly 2010, Vienna, Austria. 29