1. NCAR CGD Seminar June 2015 Disruption of the European Climate Seasonal Clock in a warming world Christophe Cassou (Cerfacs) Julien Cattiaux (Météo-France)

2. NCAR CGD Seminar June 2015 “Always blame global warming!” The polar vortex syndrome

3. NCAR CGD Seminar June 2015 Easy … but …

4. NCAR CGD Seminar June 2015 Temperature anomalies [5-12 Feb 2012] “Always blame Blocking!” 850hPa wind anomaliesPressure anomalies H

5. NCAR CGD Seminar June 2015 Temperature anomalies [20-25 July 2006] “Always blame Blocking!” H 850hPa wind anomaliesPressure anomalies

6. NCAR CGD Seminar June 2015 Temperature anomalies [20-25 July 2006] “Always blame Blocking!” H Pressure anomalies

7. NCAR CGD Seminar June 2015 Pressure anomalies [20-25 July 2006] H “Always blame Blocking and global warming!”

8. NCAR CGD Seminar June 2015 The blocking syndrome BLOCKING WILL CAUSE WARMER SUMMERS! BLOCKING WILL CAUSE WARMER SUMMERS! BLOCKING WILL CAUSE COLDER WARMER SUMMERS! WINTERS

9. NCAR CGD Seminar June 2015 Communication is an art… BLOCKING

10. NCAR CGD Seminar June 2015 The seasonality of atm. circulation & Temp. over Europe Temperature anomalies Pressure anomalies 850hPa wind anomalies The 2012 European cold wave The 2006 European heat wave

11. NCAR CGD Seminar June 2015  Evidence for strong seasonality in the atmos circulation temperature relationship.  1. Choice of the metric  2. PDF  Model  Climate Change effect  Summer starting dates  Attribution simulation (CMIP5)  Mordicus  Mechanims: snow and not land-sea contrast  Work in observation today.  Winter: no change: aerosols, snow Global warming, everywhere!

12. NCAR CGD Seminar June 2015 Data: NCEP-NCAR reanalysis DJF EOF modes of variability from winter days [1950-2012] JJA EOF modes of variability from summer days [1950-2012] Seasonality of the North Atlantic daily atm. circulation

13. NCAR CGD Seminar June 2015 Data: NCEP-NCAR reanalysis DJF EOF modes of variability from winter days [1950-2012] JJA EOF modes of variability from summer days [1950-2012] Seasonality of the North Atlantic daily atm. circulation  Northward migration of the centers of action and modes of variability but for blocking

14. NCAR CGD Seminar June 2015 Data: NCEP-NCAR reanalysis DJF EOF modes of variability from winter days [1950-2012] JJA EOF modes of variability from summer days [1950-2012] Definition of a European circulation index  Northward migration of the centers of action and modes of variability but for blocking Definition of a annual daily box-average pressure index

15. NCAR CGD Seminar June 2015 Seasonal relationship between circulation and temp. (1) Summer Surface temperature compositesWinter Surface temperature composites Data: NCEP-NCAR reanalysis

16. NCAR CGD Seminar June 2015 Seasonal relationship between circulation and temp. (2) Winter Surface temperature compositesSummer Surface temperature composites + ECA dataset (dots)Data: NCEP-NCAR reanalysis

17. NCAR CGD Seminar June 2015 Definition of a western-Europe temperature index Winter Surface temperature compositesSummer Surface temperature composites + ECA dataset (dots)Data: NCEP-NCAR reanalysis

18. NCAR CGD Seminar June 2015 The seasonal clock of the European climate Strength of the regression between PSL index & 2m-TEMP index 0.33 o C/hPa 0.66 o C/hPa 1 o C/hPa Neg. Reg/Corr.Pos. Reg/Corr.

19. NCAR CGD Seminar June 2015 The seasonal clock of the European climate Neg. Reg/Corr.Pos. Reg/Corr.

20. NCAR CGD Seminar June 2015 Neg. Reg/Corr.Pos. Reg/Corr. The seasonal clock of the European climate

21. NCAR CGD Seminar June 2015 Neg. Reg/Corr.Pos. Reg/Corr. Uncertainties for the seasonal clock (NCEP) NCEP PSL / 2mT ECA NCEP PSL / 2mT NCEP

22. NCAR CGD Seminar June 2015 Neg. Reg/Corr.Pos. Reg/Corr. x 20CR PSL / 2mT 20CR NCEP PSL / 2mT ECA NCEP PSL / 2mT NCEP Uncertainties for the seasonal clock (20CR)

23. NCAR CGD Seminar June 2015 BLOCKING, everywhere! Bilan ici et ojectives Modeles Mettre quelque part le nombre de jours traites.

24. NCAR CGD Seminar June 2015 Evaluation of the CNRM-CM5 model NCEP + ECA observational datasets (1950-2010) CNRM-CM5 historical simulation (1950-2010)

25. NCAR CGD Seminar June 2015 Obs. envelop HIST. envelop  The CNRM-CM5 model reproduces very well the European seasonal clock. Neg. Reg/Corr. The CNRM-CM5 seasonal clock  There is a slight underestimation of the PSL/TAS relationship for summer months (July and May)

26. NCAR CGD Seminar June 2015 Seasonal clock in [2070-2100] in RCP85 PiControl [1000 years]  1. Considerable reduction of the PSL/TAS relation in late winter/early spring  2. Clear increase of of the PSL/TAS relation in summer  3. No significant change in PSL/TAS relation in fall

27. NCAR CGD Seminar June 2015 Winter changes PDF for PSL Winter days (PiControl) PDF for Temp. Winter days (PiControl)

28. NCAR CGD Seminar June 2015 Winter changes PDF for PSL Winter days (PiControl) (RCP85) PDF for Temp. Winter days (PiControl) (RCP85)

29. NCAR CGD Seminar June 2015 (Mean corrected RCP85) Winter changes PDF for PSL Winter days (PiControl) PDF for Temp. Winter days (PiControl)  Cold extremes warm more than the mean  Mild extremes warm less the mean  Conditional change of 2m- Temperature reduction of variance  Zonal flows are less efficient to bring heat inland  Blocking flows are less efficient to bring cold westward

30. NCAR CGD Seminar June 2015 Summer changes

31. NCAR CGD Seminar June 2015 Summer changes  Loss of PSL/Temp relationship in winter due to reduced conditional variance of Temperature  Increase of PSL/Temp relationship in summer due to increase variance of Temperature (less dependant on atm. circulation)

32. NCAR CGD Seminar June 2015 Change in zonal gradients  2070-2100 East-West Contrast (EWC) of January = EWC in March of 1970-2000 ---> Two month seasonal advance  Maximum change in summer for land sea contrast ---> One month seasonal advance

33. NCAR CGD Seminar June 2015 BLOCKING, everywhere! Bilan des mecanismes des changements de variance. Annonce de la summer date (humour sur la recherche de la non-significativite). Mettre mot detectable Definition de la metrique. Mettre aussi une balance avec radiatif et advection

34. NCAR CGD Seminar June 2015  The summer starting date is defined as the day where the correlation between PSL and West Temp. indices crosses 0  The winter starting date is defined as the day where the correlation between PSL and West Temp. indices crosses 0 31 st of March [1980-2010] The summer starting date NCEP 20CR PiCtl 12 April 10-member Historical

35. NCAR CGD Seminar June 2015  The summer starting date is defined as the day where the correlation between PSL and West Temp. indices crosses 0  The winter starting date is defined as the day where the correlation between PSL and West Temp. indices crosses 0 The summer starting date (historical period) NCEP 20CR PiCtl 10-member Historical  Earlier onset of summer by ~10 days between the 1950’s and the 1990’s (~2.5 days/decade trend)  On the verge of detectability for this metric in presence of strong interannual variability

36. NCAR CGD Seminar June 2015 The summer starting date (the XXI st century under RCP85) NCEP 20CR PiCtl 10-member Historical  Earlier onset of summer by ~10 days between the 1950’s and the 1990’s (~2.5 days/decade trend)  On the verge of detectability for this metric in presence of strong interannual variability  Additional ~15 day winter shortening by [2070-2100]  The sharpest trend is now!

37. NCAR CGD Seminar June 2015 Ensemble Means Detection and attribution PiCtl  No volcanic eruption [1920-1960]  The observed current winter shortening is attributable to GHG forcing …  … But modulated by aerosols forcings

38. NCAR CGD Seminar June 2015 Detection and attribution  Agreement between observed very late summer onset in the 1950-1960 and HISTANT simulations. Luck? Sampling? True?  Origin of the observed earlier summer onset at the beginning of the 20 th century. Quality of the data? Atlantic Multidecadal Variability (AMV) influences?

39. NCAR CGD Seminar June 2015 Dedicated simulations : the MORDICUS project  Definition of the SPEEDY-attribution runs for processed-oriented approach  1850-1990 anthropogenic aerosols trends contracted in 30 years --> 12 members of 30yr starting from PiControl  Doubling CO 2 in 30 years --> 12 members of 30yr starting from PiControl Confirmation of the aerosol forcing on the summer starting date (delay by X days) Confirmation of the GHG forcing on the summer starting date (advance by X days)  AMO influences: --> 12 members of 30yr AMO+ and 12 members of 30yr AMO- starting from PiControl AMO + AMO - No significant impact of AMO phases in CNRM-CM5

40. NCAR CGD Seminar June 2015 Mechanisms : land-sea contrast versus East-West gradient  Change in March Land-Sea contrast is NOT responsible for the ongoing trend  Reduction in Eastern-Western Europe temp. gradient in March is responsible for the ongoing earlier summer: role of Eastern Europe Snow decline Snow cover (Eastern Europe) Land-Sea contrast

41. NCAR CGD Seminar June 2015 Comparison between observed and model trends for snow cover Snow cover (Eastern Europe)  Reduction in Eastern-Western Europe temp. gradient in March is responsible for the ongoing earlier summer: role of Eastern Europe Snow decline

42. NCAR CGD Seminar June 2015 Can we find year-to-come analogs today? 199620062013 199020072014

43. NCAR CGD Seminar June 2015 Can we find year-to-come analog today? ---> YES! 199620062013 199020072014 Snow years Snow-free years upper-tercile

44. NCAR CGD Seminar June 2015 BLOCKING, everywhere! Mettre ici les cartes des z500 et les cartes de neige de Fev? De Mars? Annonce de la summer date (humour sur la recherche de la non-significativite). Mettre le nombre dejours. Mettre graphe Yohan in caseof question MORDICUS. Vanter les merrites de la metrique: integral

45. NCAR CGD Seminar June 2015 The winter starting date (the XXI st century under RCP85) NCEP 20CR PiCtl 10-member Historical  No clear signal for winter starting dates

46. NCAR CGD Seminar June 2015 Detection and attribution (winter) PiCtl  No volcanic eruption [1920-1960]  GHG forcing leads to later winter onset …  … but strongly counteracted by anthropogenic aerosols forcing Ensemble Means

47. NCAR CGD Seminar June 2015 PiCtl  Confirmation of weak GHG forcing for later winter onset from MORDICUS experiments…  Confirmation of strong aerosols forcing for earlier winter onset from MORDICUS project Ensemble Means Dedicated simulations : the MORDICUS project

48. NCAR CGD Seminar June 2015 Thanks for your attention