1. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Predictability of weather and climate What have we learned from comprehensive modeling studies? Lennart Bengtsson MPI for Met. Hamburg ESSC, Uni. Reading Many thanks to J. Shukla

2. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science We may regard the present state of the universe as the effect of its past and the cause of its future. An intellect which at a certain moment would know all forces that set nature in motion, and all positions of all items of which nature is composed, if this intellect were also vast enough to submit these data to analysis, it would embrace in a single formula the movements of the greatest bodies of the universe and those of the tiniest atom; for such an intellect nothing would be uncertain and the future just like the past would be present before its eyes. Laplace Essai philosophique sur les probabilités

3. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science CLIMATE PREDICTION AND CHAOS For want of a nail, the shoe was lost; For want of a shoe, the horse was lost; For want of a horse, the rider was lost; For want of a rider, the battle was lost; For want of a battle, the kingdom was lost

4. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Predictability of weather

5. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science St. Petersburg prediction 10.1 2006 17th onward ca -30 C

6. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Example of ultra-high predictability Observed and simulated QBO Note the marked changes in wind direction at 10-30 hPa every 26-28 month

7. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Predictability of weather and climate. What have we learned from comprehensive modeling studies? Predictability of atmospheric flow (from mid latitude weather prediction to the quasi-biennal oscillation) Predictability of weather (how close are we to the limit?) Coupled ocean atmosphere modes (El Nino-Southern Oscillation) What do we mean by climate predictability? (what is predictable?) Climate and climate change predictability Concluding remarks

8. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science A Fundamental Question in Weather Predictability A Dynamical System is : TYPE 1 – characterized by an infinite range of predictability TYPE 2 – the range of predictability is finite, but can be increased indefinitely by decreasing the size of the initial error TYPE 3 – the range of predictability is finite and intrinsically limited Does the Weather Constitute a Type 2 or a Type 3 System?

9. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science The Growth of Very Small Errors Basic Idea – Reduce the Size of the Initial Error by putting it on smaller and smaller scales Ultimate Predictability controlled by the predictability time T = time necessary for the error to propagate upscale from very, very small initial scale to a finite, pre-chosen scale How does T behave as the initial error gets infinitely small? This tells us if we have TYPE 2 or TYPE 3 behavior! For a Spectrum E(k) ~ k -3 or steeper : T becomes infinite (thus TYPE 2) For a Spectrum E(k) less steep than k -3 : T is finite (thus TYPE 3)

10. Nastrom and Gage, 1985: A climatology of atmospheric wavenumber spectra of wind and temperature observed by commercial aircraft. J. Atmos. Sci., 42, 950–960.

11. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Does the Observed -5/3 Spectrum Imply that the Range of Predictability Cannot be Lengthened by Reducing Initial Error? Perhaps the eddies associated with the observed -5/3 spectrum do not interact with the large scale

12. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Predictability of weather and climate. What have we learned from comprehensive modeling studies? Predictability of atmospheric flow (from mid latitude weather prediction to the quasi-biennal oscillation) Predictability of weather (how close are we to the limit?) Coupled ocean atmosphere modes (El Nino-Southern Oscillation) What do we mean by climate predictability? (what is predictable?) Climate and climate change predictability Concluding remarks

13. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Improvements in NWP from Miyakoda (1972) to 2002. Courtesy ECMWF How long to get to D+10 in winter?

14. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science

15. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science The principle of error reduction in data assimilation

16. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Improvement in medium-range forecast skill 12-month running mean of anomaly correlation (%) of 500hPa height forecasts

17. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Lorenz, E. N., 1982: Atmospheric Predictability Experiments with a Large Numerical Model. Tellus, 34, 505-513 Estimates of the lower and upper bounds of predictability of instantaneous weather patterns for ECMWF forecast system Lower bound: skill of current operational forecasting procedures Upper bound: Growth of initial error, defined as the difference between two forecasts valid at the same time (Lorenz curves) Additional improvements at extended range may be realized if the one-day forecast is capable of being improved significantly.

18. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science

19. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Predictive skill ( Z 500 hPa) for the NH and predictability estimates ( for 6 ( red) and 24 hr (blue) increments)

20. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Evolution of 1-Day Forecast Error, Lorenz Error Growth, and Forecast Skill for ECMWF Model (500 hPa NH Winter) 2007 8 1.2* 0.91 From ECMW *est

21. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science ECMWF EPS: Forecast Started 8 th January 2005 00UTC (GUDRUN) From L Froude, ESSC

22. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science ECMWF EPS: Forecast Started 6 th January 2005 00UTC From L Froude, ESSC

23. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Predictive skill and predictability of storm tracks for different observing systems NH SH From L Froude, ESSC

24. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Conclusions Weather predictability Predictability of actual weather is limited to a few days. Predictability of synoptic weather systems is likely limited by ca two weeks. Improvements has come through smaller initial errors due to better observations and more advanced data- assimilation. Predictability of the general weather type varies between different regions, for different seasons and for different situations and can be from weeks to several months. There are atmospheric patterns such as QBO that have almost unlimited predictability.

25. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Predictability of weather and climate. What have we learned from comprehensive modeling studies? Predictability of atmospheric flow (from mid latitude weather prediction to the quasi-biennal oscillation) Predictability of weather (how close are we to the limit?) Coupled ocean atmosphere modes (El Nino-Southern Oscillation) What do we mean by climate predictability? (what is predictable?) Climate and climate change predictability Concluding remarks

26. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science

27. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science 1998 JFM SST [ o C] JFM SST Climatology [ o C] 1998 JFM SST Anomaly [ o C] El Nino/Southern Oscillation

28. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science

29. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science

30. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science

31. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science El Nino changes precipitation patterns

32. Evolution of Climate Models 1980-2000 Model-simulated and observed 500 hPa height anomaly (m) 1983 minus 1989

33. Vintage 2000 AGCM

34. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science 20 Years: 1980-1999 4 Times per Year: Jan., Apr., Jul., Oct. 6 Member Ensembles Kirtman, 2003 Current Limit of Predictability of ENSO (Nino3.4) Potential Limit of Predictability of ENSO

35. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Prediction of Atlantic hurricanes with a general circulation model integrated over 30 years ECHAM5/OMERA-40

36. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Predictability of large-scale climate anomaly patterns The predictability of ENSO is likely to be from several months to a few years. There are large variations in predictability. Present predictability assessment suffers from rather poor coupled models and later work is expected to change this. The same is true for well developed land surface patterns. Long term anomalies over Europe (NAO) have limited predictability The fact that very long semi-persistent pattern occur both in reality and in models suggest that predictability in some regions (such as in the Sahel region) are longer. Here we need more active basic research.

37. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Predictability of weather and climate. What have we learned from comprehensive modeling studies? Predictability of atmospheric flow (from mid latitude weather prediction to the quasi-biennal oscillation) Predictability of weather (how close are we to the limit?) Coupled ocean atmosphere modes (El Nino-Southern Oscillation) What do we mean by climate predictability? (what is predictable?) Climate and climate change predictability Concluding remarks

38. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Köppen climate zones Main groups A: Tropical rainy climate, all months > +18 C B: Dry climate, Evaporation > Precipitation C: Mild humid climate, coldest month +18 C - -3 C D: Snowy - forest climate, coldest month +10 E: Polar climate, warmest month < +10 C ET: Tundra climate, warmest month > 0 C Subgroups f : Moist, no dry seasons w: Dry season in winter s : Dry season in summer

39. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science ECHAM5 simulated ERA40 determined from analyses. Köppen climate zones

40. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Warmest and coldest season in Europe 1500-2003 Luterbacher et al(2004), Xoplaki et al (2005)

41. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science 50-year trends >0.23 corresponds to 95% significance T P Z 850 Sea ice

42. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Observation and model statistics Luterbacher et al., 2005 ( Temp. in C)

43. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Climate predictability Internal climate modes lasting up to several decades are likely to exist in the climate system. Whether these are predictable is still an open question Model studies suggest that such internal modes have dominated climate variations during the last several centuries It is hardly feasible to infer any changes in external forcing from meteorological records for the period 1500 to 1900. Models are capable to reproduce the observed climatology with considerably accuracy ( e.g.Koeppen)

44. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Predictability of weather and climate. What have we learned from comprehensive modeling studies? Predictability of atmospheric flow (from mid latitude weather prediction to the quasi-biennal oscillation) Predictability of weather (how close are we to the limit?) Coupled ocean atmosphere modes (El Nino-Southern Oscillation) What do we mean by climate predictability? (what is predictable?) Climate and climate change predictability Concluding remarks

45. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Delworth and Knutson, 2000 Monte-Carlo simulations with a coupled AO GCM: one out five simulations almost perfectly reproduced the observed global temperature variability. obsexp 3

46. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Resultat från den senaste klimatutvärderingen Observerad och beräknad temperaturändring

47. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science

48. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Coupled Model T63L31 Present climate Future climate

49. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science

50. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Predictability of snow in Germany

51. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Ensemble climate trends averaged for different time-periods (T/decade) 1-30 years 1-80 years

52. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Climate change predictability Changes in climate patterns during the last 50 years are now with high probability due to changes in atmospheric composition (greenhouse gases and aerosols) The trade off between the two cannot easily be done as they both have very similar climate pattern signatures. It can well be that we are underestimating the effect of greenhouse gases and overestimating reflecting aerosols or vice versa However, a marked positive feedback from anthropogenic greenhouse gases via water vapor and surface albedo is most likely. Future climate scenarios include considerable internal regional variations which can mask or enhance climate warming for several decades. Typical examples from the last century are the warm 1930s and 40s and cold 1960s and 70s. Robust climate change trends for specific regions require probably 50-100 years

53. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Predictability of weather and climate. What have we learned from comprehensive modeling studies? Predictability of atmospheric flow (from mid latitude weather prediction to the quasi-biennal oscillation) Predictability of weather (how close are we to the limit?) Coupled ocean atmosphere modes (El Nino-Southern Oscillation) What do we mean by climate predictability? (what is predictable?) Climate and climate change predictability Concluding remarks

54. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science Concluding Remarks The largest obstacles in realizing the potential predictability of weather and climate are inaccurate models and insufficient observations, rather than an intrinsic limit of predictability. –In the last 30 years, most improvements in weather forecast skill have arisen due to improvements in models and assimilation techniques The next big challenge is to build a hypothetical perfect model which can replicate the statistical properties of past observed climate (means, variances, covariances and patterns of covariability), and use this model to estimate the limits of weather and climate predictability –The model must represent ALL relevant phenomena, including ocean, atmosphere, and land surface processes and the interactions among them

55. L Bengtsson 14.6.07 Bosön, Stockholm Multiscale modeling and simulation in Science END Any questions?