Response of the North Atlantic jet and its variability to increased greenhouse gasses in the CMIP5 models 1,3 Lorenzo Polvani 2 Dennis Hartman 3 1 Lamont-Doherty Earth Observatory 2 Columbia University 3 University of Washington Atlantic Sector Variability & Change Oct. 17, 2012
North Atlantic Oscillation: primary mode of variability +NAO -NAO http://www.ldeo.columbia.edu/res/pi/nao/
CMIP5 Results How will eddy-driven jet variability respond to climate change?
CMIP5 Results How will eddy-driven jet variability respond to climate change? How do changes in the jet variability relate to eddy/wave activity? absolute vorticity 90 W 60 W 30 W 30 S 45 S 60 S wave breaking blocking recent results on wave heights LDEO Francis, & Vavrus (2012); GRL
What did IPCC AR4 say? - focused on trends - indicates poleward shift of the mean position Miller, Schmidt et al. (2006); JGR
What did IPCC AR4 say? - focused on trends - indicates poleward shift of the mean position time-mean jet NAO anomaly pattern JET + -
What do we mean by variability? Wittman, Charlton et al. (2005); JCLI
Barotropic model: dependence of variability on latitude Variability of jet changes to pulse at high latitudes LDEO
Barotropic model: dependence of variability on latitude MECHANISM: waves cannot propagate and break at high latitudes (beta is small), so no eddy-mean flow feedback to make jet wobble Variability of jet changes to pulse at high latitudes LDEO
CMIP5 data
Jet definitions 70 (a) 60-850-700 hpa winds - 10-day lowpass filtered - jet latitude time series latitude (deg.) 50 40 jet latitude 30 20 5 0 5 10 15 zonal wind (m/s) Barnes & Polvani (2012); submitted
Mean jet position 51 (b) North Atlantic 50 MERRA jet latitude (deg.) 49 48 47 46 45 - poleward jet shift avg. change 46 48 50 Historical jet latitude (deg.) picontrol Historical RCP4.5 RCP8.5 Barnes & Polvani (2012); submitted
Mean jet position (seasonal shifts) June-Sept. Dec.-Mar. 54 North Atlantic (JJAS) 50 North Atlantic (DJFM) jet latitude (deg.) 52 50 48 46 44 avg. change picontrol Historical RCP4.5 RCP8.5 jet latitude (deg.) 48 46 44 42 40 avg. change picontrol Historical RCP4.5 RCP8.5 44 46 48 50 52 54 Historical jet latitude (deg.) 40 42 44 46 48 50 Historical jet latitude (deg.) - shift depends on season
Daily jet latitude histograms 20 (b) - standard deviation of daily jet latitude decreases jet latitude anomaly (deg.) 15 10 5 0 5 10 15 20 Historical [46.6 o N, 6.73 o ] RCP8.5 [47.2 o N, 5.89 o ] 0 0.02 0.04 0.06 0.08 0.1 0.12 relative frequency GFDL-ESM2M
Standard deviation of jet latitude 9 (b) North Atlantic 8.5 - decrease in standard deviation when jet shifts poleward standard deviation (deg.) 8 7.5 7 avg. change 6.5 6 42 44 46 48 50 52 jet latitude (deg.) Barnes & Polvani (2012); submitted LDEO
EOF Analysis calculate EOF 1 of sector-averaged low-level winds
EOF 1 pattern 30 (a) EOF 1 - less wobble, more pulse relative latitude (deg.) 20 10 0 10 20 30 Historical RCP8.5 1 0.5 0 0.5 1 normalized zonal wind anomaly IPSL-CM5A-MR
EOF 1 pattern versus jet latitude 80 70 (c) North Atlantic EOF1 8 6 - smaller wobble for higher-latitude jets 4 latitude (deg.) 60 50 40 jet latitude 2 0 2 4 EOF anomaly [m s 1 ] relative latitude (deg.) 30 20 10 0 10 20 30 (a) EOF 1 Historical RCP8.5 1 0.5 0 0.5 1 normalized zonal wind anomaly 30 6 20 1 2 1 4 11 23 12 11 5 2 42 44 46 48 50 52 mean jet latitude (deg.) 8 Barnes & Polvani (2012); submitted LDEO
EOF 1 wobble with climate change - decrease in jet wobble with climate change predicted by models - signal is less clear than when plotted against latitude alone (so other important processes are at play here) Barnes & Polvani (2012); submitted jet wobble for EOF1 (rel. lat. in deg.) 12 11 10 9 8 7 6 5 4 3 2 (b) North Atlantic avg. change 42 44 46 48 50 52 jet latitude (deg.)
Eddy activity in the future Large-scale Rossby wave breaking is linked to jet variability Previous results suggest that wave breaking will decrease over the Atlantic as the jet shifts poleward... (Barnes & Hartmann (2010, 2011, 2012)) Does it? D09117 BARNES AND HARTMANN: WAVE BREAKING AND CLIMATE CHAN examples of wave breaking LDEO Figure 1. Snapshots of instantaneous fields of (a) absolute vorticity in the barotropic
Detecting wave breaking at 250 hpa absolute vorticity 90 W 60 W 30 W 30 S 45 S 1. find breaking contours of vorticity 2. group contours in wave breaking events 3. look at tilt to determine orientation of breaking 60 S Barnes & Hartmann (2012b); JGR
Detecting wave breaking at 250 hpa absolute vorticity 90 W 60 W 30 W wave height 30 S 45 S 1. find breaking contours of vorticity 2. group contours in wave breaking events 3. look at tilt to determine orientation of breaking 60 S Barnes & Hartmann (2012b); JGR
Wave breaking vs. jet latitude 70 (d) North Atlantic AWB 0.1 0.09 60 0.08 latitude (deg.) 50 40 30 20 jet latitude 0.07 0.06 0.05 0.04 0.03 RWB frequency [year 1 deg. 2 ] - equatorward wave breaking moves with the jet 0.02 10 0.01 0 1 2 1 4 11 23 12 11 5 2 42 44 46 48 50 52 mean jet latitude (deg.) 0 Barnes & Polvani (2012); submitted
Wave breaking vs. jet latitude 70 (e) North Atlantic decrease CWB 0.05 0.045 60 0.04 latitude (deg.) 50 40 30 20 jet latitude 0.035 0.03 0.025 0.02 0.015 RWB frequency [year 1 deg. 2 ] - cyclonic wave breaking decreases on poleward jet flank - wave breaking appears to have a meridional ceiling 0.01 10 0.005 0 1 2 1 4 11 23 12 11 5 2 42 44 46 48 50 52 mean jet latitude (deg.) 0 Barnes & Polvani (2012); submitted
Wave breaking vs. jet latitude latitude (deg.) 70 60 50 40 30 20 (e) North Atlantic cyclonic wave CWB breaking decreases 0.05 0.045 with climate warming jet latitude in the models 0.04 0.035 0.03 0.025 0.02 0.015 0.01 RWB frequency [year 1 deg. 2 ] cyclonic wavebreaking frequency (year 1 ) 70 65 60 55 50 45 (f) North Atlantic avg. change CWB 10 0 1 2 1 4 11 23 12 11 5 2 42 44 46 48 50 52 mean jet latitude (deg.) 0.005 0 40 42 44 46 48 50 52 jet latitude (deg.) Barnes & Polvani (2012); submitted
What does this say about blocking in the future? Quarterly Journal of the Royal Meteorological Society Q. J. R. Meteorol. Soc. 138: 1285 1296, July 2012 A Wave-breaking characteristics of midlatitude blocking G. Masato, a * B. J. Hoskins b and T. J. Woollings a a Department of Meteorology, University of Reading, UK b Grantham Institute, Imperial College, London, UK Rossby wave breaking is identified as a key process in blocking occurrence, as it provides the mechanism for the meridional reversal pattern typical of blocking.
CMIP3 Atlantic blocking frequency change in days blocked per year LDEO 5 0 5 10 15 20 25 Northern Hemisphere bccr bcm2 0 cccma cgcm3 1 cnrm cm3 significant at 95% csiro mk3 0 csiro mk3 5 gfdl cm2 0 gfdl cm2 1 giss model e r inmcm3 0 ipsl cm4 miroc3 2 medres miub echo g mri cgcm2 3 2a mpi echam5 blocking frequency decreases with warming in CMIP3 Barnes, Slingo, Woollings (2012); CDYN
CMIP5 blocking frequency from Dunn-Siouin & Son (2012) Atlantic Atlantic Asia Asia Pacific blocking frequency decreases with warming in CMIP5 Pacific Dunn-Sigouin & Son (2012); submitted, Fig. 1 units are days/year gridpoint is blocked
What about blocking duration? - No measurable change in blocking duration in CMIP3 by Barnes, Slingo & Woollings (2012) - Difficult to determine if any change in blocking duration in CMIP5 by Dunn-Sigouin & Son (2012) NO CHANGE IN BLOCKING DURATION suggests that physics of blocking doesn t change, just the number of events
How does this relate to recent work? GEOPHYSICAL RESEARCH LETTERS, VOL. 39, L06801, doi:10.1029/2012gl051000, 2012 Evidence linking Arctic amplification to extreme weather in mid-latitudes Jennifer A. Francis 1 and Stephen J. Vavrus 2 Polar Amplification leads to: - weakened zonal winds - increased wave amplitude - increased blocking frequency - increased blocking duration (from slower wave progression)
How does this relate to recent work? GEOPHYSICAL RESEARCH LETTERS, VOL. 39, L06801, doi:10.1029/2012gl051000, 2012 Evidence linking Arctic amplification to extreme weather in mid-latitudes Jennifer A. Francis 1 and Stephen J. Vavrus 2 Polar Amplification leads to: - weakened zonal winds - increased wave amplitude X jet speed (m/s) 15 14 13 (b) North Atlantic avg. change - increased blocking frequency - increased blocking duration (from slower wave progression) 12 11 42 44 46 48 50 52 jet latitude (deg.)
How does this relate to recent work? GEOPHYSICAL RESEARCH LETTERS, VOL. 39, L06801, doi:10.1029/2012gl051000, 2012 Evidence linking Arctic amplification to extreme weather in mid-latitudes Jennifer A. Francis 1 and Stephen J. Vavrus 2 0.03 Atlantic wave heights (JJAS) (RCP8.5 - Historical) Polar Amplification leads to: - weakened zonal winds - increased wave amplitude - increased blocking frequency - increased blocking duration (from slower wave progression) X X relative frequency difference 0.02 0.01 0 0.01 0.02 preliminary! 10 20 30 40 meridional height of wave (deg.)
How does this relate to recent work? GEOPHYSICAL RESEARCH LETTERS, VOL. 39, L06801, doi:10.1029/2012gl051000, 2012 Evidence linking Arctic amplification to extreme weather in mid-latitudes Jennifer A. Francis 1 and Stephen J. Vavrus 2 Polar Amplification leads to: - weakened zonal winds - increased wave amplitude X X - increased blocking frequency - increased blocking duration (from slower wave progression) X X
Conclusions - models still struggle to get correct jet position with climate warming, CMIP5 models show... - a poleward shift of the jet (although seasonally dependent) - amount of wobble of NAO decreases (especially if grouped w.r.t. to jet latitude) - wave breaking and blocking frequency decreases
EXTRA SLIDES
Mean jet position (seasonal shifts) June-Sept. Dec.-Mar. 54 North Atlantic (JJAS) 50 North Atlantic (DJFM) jet latitude (deg.) 52 50 48 46 44 avg. change picontrol Historical RCP4.5 RCP8.5 jet latitude (deg.) 48 46 44 42 40 avg. change picontrol Historical RCP4.5 RCP8.5 44 46 48 50 52 54 Historical jet latitude (deg.) 40 42 44 46 48 50 Historical jet latitude (deg.) - shift is dependent on season
Skewness of jet latitude MERRA North Atlantic 1.25 1 Southern Hemisphere North Atlantic 0.75 - skewness decreases with jet latitude skewness 0.5 0.25 0 0.25 Barnes & Polvani (2012); submitted LDEO 0.5 0.75 picontrol Historical RCP4.5 RCP8.5 42 44 46 48 50 52 54 jet latitude (deg.)
Barotropic model results leading EOF describes less of a shift at high and low latitudes Barnes & Hartmann (2011); JAS Amount of Z jet EOF1 shift shift for of annular jet (deg.) mode (deg.) 6 5 4 3 2 1 EOF shift (c) wobbling pulsing pulsing 20 30 40 50 60 jet latitude stir (deg. (deg. N) N)
Idealized model results from Garfinkel et al. (2012) var exp. jet shift 0.4 0.3 0.2 m=0.02±0.01, 0.0072±0.009 (e) 0.1 60 40 20 jet latitude var exp. jet speed m= 0.005±0.004, 0.0075±0.005 0.2 0.15 0.1 (f) 0.05 60 40 20 jet latitude Garfinkel, Waugh & Gerber (2012); submitted
EOF 1 pattern versus jet latitude 80 (c) North Atlantic EOF1 8 80 (c) North Atlantic EOF1 8 70 6 70 6 4 4 latitude (deg.) 60 50 40 jet latitude 2 0 2 4 EOF anomaly [m s 1 ] latitude (deg.) 60 50 40 jet latitude 2 0 2 4 EOF anomaly [m s 1 ] 30 6 30 6 20 1 2 1 4 11 23 12 11 5 2 42 44 46 48 50 52 mean jet latitude (deg.) 8 20 1 2 1 4 11 23 12 11 5 2 8 42 44 46 48 50 52 mean jet latitude (deg.) Barnes & Polvani (2012); submitted LDEO
EOF 1 & 2 80 (c) North Atlantic EOF1 80 8 (d) North Atlantic EOF2 8 70 6 70 6 4 4 latitude (deg.) 60 50 40 latitude (deg.) 2 60 050 2 40 4 EOF anomaly [m s 1 ] 2 0 2 4 EOF anomaly [m s 1 ] 30 30 6 6 20 1 2 1 4 11 23 12 11 5 2 42 44 46 48 50 52 mean jet latitude (deg.) 8 20 1 2 1 4 11 23 12 11 5 2 42 44 46 48 50 52 mean jet latitude (deg.) 8 LDEO
Mean jet speed in CMIP5 (b) North Atlantic 15 14 - no obvious changes in jet speed jet speed (m/s) 13 avg. change 12 11 42 44 46 48 50 52 jet latitude (deg.) Barnes & Polvani (2012); submitted
CMIP3 Atlantic blocking frequency change in days blocked per year 5 0 5 10 15 20 25 Northern Hemisphere bccr bcm2 0 cccma cgcm3 1 cnrm cm3 significant at 95% csiro mk3 0 csiro mk3 5 gfdl cm2 0 gfdl cm2 1 giss model e r inmcm3 0 ipsl cm4 miroc3 2 medres miub echo g mri cgcm2 3 2a mpi echam5 change in days blocked per year 20 0 20 40 60 (b) EuroAtlantic (300 o E-30 o E) bccr bcm2 0 ma cgcm3 1 DJF MAM JJA SON cnrm cm3 csiro mk3 0 csiro mk3 5 gfdl cm2 0 gfdl cm2 1 ss model e r inmcm3 0 ipsl cm4 c3 2 medres miub echo g cgcm2 3 2a mpi echam5 blocking frequency decreases in the future Barnes, Slingo, Woollings (2012); CDYN
Seasonality from Dunn-Siouin & Son (2012) blocking frequency decreases July-Jan. Dunn-Sigouin & Son (2012); submitted, Fig. 2