1 / 41

Monthly Forecasting with Ensembles

Monthly Forecasting with Ensembles. Fr é d é ric Vitart European Centre for Medium-Range Weather Forecasts. Index. The ECMWF monthly forecasting system Description Skill Some sources of predictability in the subseasonal time-scale Madden Julian Oscillation Stratospheric Sudden Warming

mulan
Download Presentation

Monthly Forecasting with Ensembles

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related