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Diagnosing the MJO in the ECMWF forecast system Research and model changes to improve the MJO prediction A cautionary ta

Research at ECMWF concerning the simulation of the Madden - Julian Oscillation Adrian Tompkins Peter Bechtold, Judith Berner, Laura Ferranti, Thomas Jung, Frederic Vitart, Nils Wedi. Diagnosing the MJO in the ECMWF forecast system Research and model changes to improve the MJO prediction

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Diagnosing the MJO in the ECMWF forecast system Research and model changes to improve the MJO prediction A cautionary ta

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  1. Research at ECMWF concerning the simulation of the Madden - Julian OscillationAdrian TompkinsPeter Bechtold, Judith Berner, Laura Ferranti, Thomas Jung, Frederic Vitart, Nils Wedi • Diagnosing the MJO in the ECMWF forecast system • Research and model changes to improve the MJO prediction • A cautionary tale!

  2. 1. MJO as a weather diagnostic • ECMWF currently produces • 10 day forecast (uncoupled) at T799 (25 km) L91 resolution • Monthly forecast (coupled) at T159 L62 • 6-month seasonal forecast (coupled) at T95L40 resolution • The prediction of the MJO is becoming a benchmark diagnostic, at least for the monthly and seasonal forecasts. • Previous work (Jung and Tompkins 2003) showed that ECMWF model (recent versions) has a eastward propagating signal, but phase speed too fast: Convectively Coupled Kelvin Wave.

  3. 850hPA Zonal Wind NCEP reanalysis ECMWF operational Analysis MJO previous work Signal visible in unfiltered data Time MJO Zhang 2005

  4. GPCP Precipitation Operations 24hr forecast Zhang 2005 Time MJO

  5. 24 hr Forecasts of the MJO? Tomorrow will see scattered showers in the north… and in the south there will be some MJO

  6. What of longer term forecasts?Internal Web-pages for monitoring of MJO in Monthly Forecasts

  7. 1st Feb And the latest forecast from 2nd March 2006 is… 200 hPa Velocity Potential anomaly 10S/10N 1st Mar

  8. 1st Feb Well, a bit of an anticlimax to be honest… 1st Mar

  9. 1st Feb 850 hPa Zonal Wind Anomaly 1st Mar

  10. Same seen in EOF analysisof Velocity Potential Vitart et al. 2003: MJO variance decreases during the first 10d by as much as 50%

  11. ERA40-Reanalysis Spectral Analysis of 40 Winter Integrations Model: IFS CY28R3 Q: Is there a crucial physically process (feedback) missing in the model or are waves being damped?

  12. 2. Further MJO Research2(a): Berner & Palmer: Stochastic superclusters Moncrieff,2004 Develop of a multi-scale cellular automaton (MSCA) for organized convection that captures the subgrid-scale forcing not represented by conventional parameterizations. • Potential to reduce systematic error by better representation of MJO (connect to ENSO) • Potential of improved skill of medium- to extended-range weather forecasts by better representation of tropical variability (Ferranti et al.,1990)

  13. Stochastic super clusters (SSC) as part of organized convection (super-gridscale) smooth scale Cartoon of idealized forcing pattern Smoothed CAPE Non-local, quasi-random,state-dependent

  14. 200hPA Velocity Potential for 6 month Forecast Analysis Control SSC Work in Progress: But clear impact on propagating signals

  15. 2(b). Nils Wedi: Theorizes on the importance of the zonal mean flow, influenced by the extra-tropics? Average for Ensemble of forecasts 50 days Sinusoidal zonal mean wind oscillation enforced in the tropics Control: No 50 day peak. Also Work in Progress

  16. Era 40 2(c): Changes for 30R2 (summer 2006) • Model physics is updates 1 or 2 times a year • Monitored for impact on wave activity • Changes to clouds, that increase upper tropospheric ice amounts and increase convective organisation through radiative feedback, appear to impact wave propagation Control NewScheme

  17. Amalgation of 10day forecasts: Velocity potential at 200 hPa Analysis 30r1 Current operations 30r2 Summer 2006

  18. Impact on monthly forecast less dramatic Velocity Potential at 200 hPa.Forecast starting on 31 December 1992 Control New Scheme Analysis

  19. 4. A Cautionary Tale: Wave sensitivity in GCMs • Convective organisation improved the propagating convective signal • What about water vapour feedback with convection? • Local moistening can “precondition” the atmosphere, making it favourable for future convection, organising convection MOIST DRY DRY

  20. A whole range of targeted sensitivity tests • Boundary Layer Theta_e • Entrainment into Updraughts ENHANCE/INHIBIT RAINFALL EVAPORATION ENHANCE ENTRAINMENT FACTOR • For example: • Increase entrainment factor • Input zonal mean humidity to convection scheme • For example: • Coverage from 5% to 30% • Double evaporation rate • Increase RH limit from 80% to 100%

  21. Effect on Convective Precipitation Increase entrainment into convection parametrized updraughts Instead of enhancing parametrized convection in moist areas and supressing in dry areas.. 25 days 25 days …the scheme is supressed and the grid-scale takes over!!!

  22. Increasing gridscale activity Increasing Large-scale activity increases peak power (K=1,2,3 15 days<p<120 days) Increasing power in convectively coupled mode Normalized Peak Power of 200 hPa Vel Pot

  23. Large-scale precipitation in Kelvin Wave temperature Large Scale Circulation • Latent heating (from cloud scheme) directly in phase with upward motion by construction. Changes in cloud scheme have large influence on incidence of grid-scale convection

  24. Convective-scale precipitation in Kelvin Wave Large Scale Circulation qe • The convection parameterization is not so constrained, and responds to PBL theta_e, CAPE, (humidity). Can provide heating out of phase, possibly damping the wave.

  25. EOF1 EOF2 Linking the convective parametrization mass-flux closure to mid-tropospheric motion as well as CAPE strengthens propagating modes but… Justifiable? Forecast Scores? 200 hPa Velocity Potential Anomaly Grid-scale rainfall anomaly Convective Parametrization rainfall anomaly

  26. Conclusions • A whistle-stop tour of MJO at ECMWF, no vertical structure discussion • Prediction of MJO falls of rapidly after the 5 to 10 day forecast range • Crucial physical mechanism missing? • Signal strongly damped by model? • Coupling & resolution do not have strong zero-order impact • ECMWF research into MJO for long term improvements: • Stochastic supercluster forcing (missing mesoscale organisation) • Extra-tropical influence on wavenumber zero • Participation in the Aqua-Planet Experiment (model intercomparison) • Model physics changes monitored for their MJO (and wave) impact • Recent enhancement of (convectively detrained) ice leads to increased convective organisation and MJO-like improvements – radiative feedback? • Warning about interpreting results from GCMs • Physics alters balance of grid-scale/parametrized convection • Grid-scale convection in phase with waves and enhances convectively coupled Kelvin wave activity

  27. The latest Aqua Planet resultsFrom Mike Blackburn & the Aqua-Planet Experiment in which ECMWF in participating That’s all, thank you!

  28. Coupling effect T159 versus T95

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