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Monthly Forecasting with Ensembles PowerPoint Presentation
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Monthly Forecasting with Ensembles

Monthly Forecasting with Ensembles

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Monthly Forecasting with Ensembles

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  1. Monthly Forecasting with Ensembles Frédéric Vitart European Centre for Medium-Range Weather Forecasts

  2. Index • The ECMWF monthly forecasting system • Description • Skill • Some sources of predictability in the subseasonal time-scale • Madden Julian Oscillation • Stratospheric Sudden Warming • Soil moisture • Extension to 46-day – Comparison with seasonal forecasts

  3. ECMWF: Weather and Climate Dynamical Forecasts Seasonal Forecasts Month 2-7 Medium-Range Forecasts Day 1-10(15) Monthly Forecast Day 10-32 Product Forecasting systems at ECMWF

  4. The ECMWF VarEPS-monthly forecasting system Current system (once a week, 51 ensemble members): EPS Integration at T639 Initial condition Day 10 Heat flux, Wind stress, P-E Day 32 Coupled forecast at TL319 Ocean only integration

  5. The ECMWF monthly forecasting system • Background statistics: • 5-member ensemble integrated at the same day and same month as the real-time time forecast over the past 18 years (a total of 90 member ensemble) • Initial conditions: ERA Interim • It runs once every week

  6. The ECMWF monthly forecasting system

  7. Problem with hindcast initial conditions Snow ANALYSIS 11 MAY Forecast of week 1 Start: 11-05-2006 Observations Probability of T2m to be in lowest tercile 100 % 0

  8. Skill of the ECMWF Monthly Forecasting System ROC score: 2-meter temperature in the upper tercile Day 5-11 Day 12-18 Day 26-32 Day 19-25

  9. Monthly Forecast: Performance over the Northern Extratropics ROC score: 2-meter temperature in the upper tercile Forecast Day 19-32 Forecast Day 12-18 Persistence of Day 5-11 Persistence of Day 5-18 Day 12-18 Day 19-32

  10. The Madden Julian Oscillation

  11. OLR anomalies - Forecast range: day 15 ERA40 28R3 29R1 31R1 32R2 29/12 05/01 12/01 days 20/01 28/01 04/04 12/02 10/04 04/05 09/06 06/07 32R3 33R1 35R1 35R3 11/07 06/08 09/08 09/09

  12. Hindcast Experiment Experimental setup: • 46 day hindcasts at T399/T255. Coupled after day 10. • 15 members • Starting dates: 1st of each month 1989-2008 • Model Cycle 32R3 (operational cycle from 11/07 to 06/08)

  13. MJO Skill scores Bivariate Correlation Bivariate RMS error Ensemble mean/ reanalysis Ensemble mean/ reanalysis Ensemble Spread “Perfect Model” Climatology

  14. Impact on the Extratropics- Z500 anomalies

  15. Impact on the Extratropics- Z500 anomalies ERA Interim 32R3 36R1_relax 36R1

  16. Impact on weather regimes Phase3+10 days Phase6+10 days NAO+ Atlantic ridge Scandinavian blocking NAO-

  17. Probabilistic skill scores – NDJFMA 1989-2008 Reliability Diagram Probability of 2-m temperature in the upper tercile Day 19-25 Europe N. Extratropics 0.04 0.03 -0.06 -0.09 Weak MJO in IC Strong MJO in IC

  18. Impact of the MJO on Brier Skill ScoresNDJFMA 1989-2008- N. Extratropics DAY 12-18 DAY 5-11 Z500 Z500 Z500 Z500 T850 T850 T850 T850 Precip Precip Precip Precip DAY 19-25 DAY 26-32 Strong MJO in IC Weak MJO in IC

  19. MJO Composite- NDJFMA Tropical storm density anomaly Vitart, 2009, GRL

  20. Tropical storm strike probability Day 5-11 Day 12-18 Day 26-32 Day 19-25 ROC AREA over SH

  21. Per. SST anomalies OGCM ML Impact of ocean-atmosphere coupling Woolnough et al, QJRMS, 2007

  22. Soil Moisture Initial Conditions

  23. GLACE2 Series 1 – Series 2 – ECMWF AMIP DAY 0-15 DAY 16-30 DAY 31-45 Courtesy Bart van den Hurk

  24. Stratospheric initial conditions

  25. Stratospheric Sudden Warmings Impact of vertical resolution . Forecast starting on 5/1/06 Forecast starting on 19/1/06 RMS error L62 RMS error L91 Spread L62 Spread L91 L91 L62

  26. Impact of Better stratospheric vertical resolution Probability that Z500 anomalies are in upper tercile 1st Feb/May/Aug/Oct 1989-2008 (80 cases) Day 12-18 Day 19-25 Day 26-32 62 levels 91 levels

  27. Stratospheric Sudden Warmings Impact of S-Svs Ensemble spread Forecast 5/01/06 Forecast 26/01/06 Control S-Svs Work with J. Barkmeijer, T. Jung and M. Leutbecher

  28. 46-day EPS experiment Comparison with System 3

  29. Global Scores 2MTM- Ensemble mean correlation with analysis August 1981-2007 SEAS- Month 2 VEPS

  30. 46-day EPS extension – DJFM – N. extra. ROC Diagram Reliability Diagram EPS Day 16-45 Seas Month 2

  31. Interannual variability of June rainfall over India1989-2007 Verification: 1ox1o gridded daily rainfall data from IMD

  32. Interannual variability of Atlantic hurricanes 1981-2007 Correlation with HURDAT

  33. Conclusion • Forecasts for days 12-18 that are generally better than climatology and persistence of day 5-11. Beyond 20 days the monthly forecast is marginally skilful. • The MJO is the main source of predictability in the northern Extratropics for weeks 3 and 4. • Extending EPS forecasts can help to produce more frequent and skilful short-range seasonal forecasts, particularly for some extreme events.

  34. Future Plans • Run the monthly forecasts twice a week • Ocean/atmosphere Coupling from day 0 • Extend forecast range to 46-60 days

  35. Multi-model combination T850 Extreme tercile probability forecast. Northern Hemisphere. DJF. 84 cases (1990-2002) ECMWF NCEP (MRF) ECMWF+NCEP Whitaker et al, 2005

  36. a) Analysis b) Operational MOFC c) MOFC CY31R2 d) VAREPS CY31R2 Test case : Summer 2003 Heat Wave Forecasts started on 23 July 2003 for 2mT anomalies for 3-9 August 2003 (fc day 12-18): impact of model cycle and upgrade to 32-day VAREPS.

  37. The ECMWF VarEPS-monthly forecasting system • A 51-member ensemble is integrated for 32 days every week • Atmospheric component: IFS with the latest operational cycle and with a T639L62 resolution till day 10 and T319L62 after day 10. • Persisted SST anomalies till day 10 and ocean-atmosphere coupling from day 10 till day 32. • Oceanic component: HOPE (from Max Plank Institute) with a zonal resolution of 1.4 degrees and 29 vertical levels • Coupling: OASIS (CERFACS). Coupling every 3 hours.

  38. Stratospheric Sudden warming- January 2009 SSW Index (T50 gradient) 15/1/2009 8/1/2009

  39. Stratospheric Sudden warming- January 2009 15/1/2009 2mtm anomaly Forecast Composite Good SW Composite Bad SW Analysis Day 19-25 Day 26-32

  40. MJO Propagation Analysis Forecast

  41. Convection changes to operational massflux scheme (CY32R3) New formulation of convective entrainment: Previously linked to moisture convergence – Now more dependent on the relative dryness of the environment New formulation of relaxation timescale used in massflux closure: Previously only varied with horizontal resolution – Now a variable that is dependent on the convective turnover timescale i.e. variable in both space and time also Impact of these changes is large including a major increase in tropical variability Bechtold et al, QJRMS, 2008