Operational MJO prediction at ECMWF Frédéric Vitart With contributions from A. Beljaar, P. Bechtold and M . Miller European Centre for Medium-Range Weather Forecasts

Outline MJO prediction using the ECMWF monthly forecasting system 2. Skill of the monthly forecasting system to predict the MJO Some sensitivity experiments Impact of changes in physic parameterization Conclusion

Forecasting systems at ECMWF Product Tool ECMWF: Weather and Climate Dynamical Forecasts Forecasting at ECMWF Medium-Range Forecasts Day 1-15 Monthly Forecast Day 1-32 Seasonal Forecasts Month 1-7 (13) Here is an overview of the ECMWF products: Medium-Range Forecasts: These are global atmosphere forecasts and ocean wave forecasts, they are produced Twice daily and they range from 1 days up to 15 days. Medium range forecasts are created by using a sophisticated numerical model that simulated the atmospheric circulation. The atmospheric model is initialized with the status of art data assimilation system. Monthly forecasts are produced Weekly, every Thursday, and they extend up to 31 days. Beyond 15 days the interactions between atmospheric circulation and ocean circulation play an important role. As a consequence of that the Monthly forecasting system consists of an Atmosphere-ocean coupled model. Seasonal forecasts are produced Monthly, every 15th , and they extend up to seven months. Those forecast are also created by an Atmosphere-ocean coupled model. Since March 2007 we also produce a limited ensemble of seasonal forecast that are extended up to 13 months. All products available for commercial use through the ECMWF Catalogue http://www.ecmwf.int/products/catalogue/ Atmospheric model Ocean model Atmospheric model Ocean model Atmospheric model

The ECMWF monthly forecasting system Coupled ocean-atmosphere integrations: a 51-member ensemble is integrated for 32 days every Thursday Atmospheric component: IFS with the latest operational cycle and with a T159L62 resolution (about 125 km) Oceanic component: HOPE (from Max Plank Institute) with a zonal resolution of 1.4 degrees and 29 vertical levels Coupling: OASIS (CERFACS). Coupling every ocean time step (1 hour) Calibration: a 5-member ensemble is integrated at the same day and same month as the real-time time forecast over the past 12 years. The forecasts beyond 15 days are computed by a coupled ocean-atmosphere system. The system is run many times for the month ahead to build up a picture of the likelihood of different weather types affecting the Europe and the entire globe. Every Thursday an ensemble of 51 forecasts is launched. The initial conditions of each forecast are perturbed to represents the uncertainties of the initial conditions. Each forecast evolves independently for 32 days. The monthly forecast products is based on probabilities and ensemble means computed by using those 51 members. The atmospheric component is the same used for the medium range but with a coarser horizontal resolution (~120Km vs 50Km ) The oceanic component has enough horizontal resolution to resolve the ocean baroclinic waves and processes confined at the Equator. (meridional resolution is variable with a max of 0.3 degree at the equator) Exchange of fluxes between atmosphere and ocean are computed every hours.

Prediction of the Madden Julian Oscillation (MJO) VP200 Monthly Forecast starting on 7 December 2007 VP200

Prediction of the Madden Julian Oscillation (MJO) Monthly Forecast starting on 7 December 2007

MJO metric (similar to Wheeler and Hendon (2004)) Forecast anomalies of OLR, U850, & U200 are obtained by subtracting the hindcast climatology of the respective fields from the forecast. The forecast anomalies are then averaged over latitudes (-15, 15). The forecast anomalies of the 3 fields are divided by the respective global standard deviations calculated from the NCEP reanalyses. The resulting anomalies are projected onto the first two EOF patterns, the latter being computed by Matt Wheeler from NCEP reanalyses. The two projection coefficient time series are further divided by the standard deviations of first two PC (also from NCEP reanalyses), to obtain the RMM12. To remove the interannual variability, a 120-day running mean of RMM12 is subtracted.

Operational MJO Prediction

+ 12-year climatology + 18-year climatology Planned unified 32-day VAREPS/monthly system Present TL159 monthly system: Initial condition Day 32 Coupled forecast at TL159 (~125 km) + 12-year climatology Future 32-day VAREPS/monthly system: EPS Integration at T399 (~50km) Coupled forecast at TL255 (~80km) Initial condition Day 10 Day 32 Heat flux, Wind stress, P-E The next upgrade of the monthly system will be a unification of the medium -range and monthly forecast. Currently the monthly forecast runs from the initial conditions defined by the operational analysis at a relatively low resolution (~120km). In future the system will start from the day 10 of the ensemble prediction system. The ensemble prediction system run at higher resolution than the current monthly forecast (50Km vs 120Km) so the 10 days forecast will benefit from the higher resolution. From days 10 the coupled system will be run at horizontal resolution of about 80km . The test version of such system has been set up and a number of forecast covering the period 20070613-20070724 have been performed. SST anomalies are persisted instead of the full SST field. This suite also produces hindcasts once a week. So far, 5 sets hindcasts (5 ensemble members, 18 years) have been produced. The cost of the forecast increases with the cube of the horizontal resolution. Ocean only integration + 18-year climatology

Skill of the MJO Prediction EXPERIMENT: A 5-member ensemble has been run every day from 15 December 1992 to 31st January 1993. The MJO diagnostic is based on the same method as in the real-time forecasts, except for: Velocity potential anomalies at 200 hPa instead of U200 Fields are averaged between 10N and 10S instead of 15N and 15S.

Skill of the MJO Prediction ERA40: 15/12/92-31/01/93 Velocity Potential 200 hPa U850 OLR

Skill of the MJO Prediction

Current operational version of the monthly forecasting system (CY32R2) Skill of the MJO Prediction Current operational version of the monthly forecasting system (CY32R2) Anomaly correlation Amplitude PC1 PC2

Impact of ocean-atmosphere coupling Cycle CY32R2 PC1 PC2 VAREPS Coupled Ocean ML

Warm ocean (skin ) layer model to represent diurnal time scale Similarity temperature profile is assumed with depth scale d representing penetration depth of solar radiation: (surface/skin temperature) (deep/bulk temperature) Prognostic equation for temperature difference between skin and bulk ocean temperature: Energy forcing from surface and solar absorption Wind and stability dependent mixing term (reduces temperature difference to 0 in strong winds) Zeng and Beljaars (2005), Geophys. Res. Lett. 32, L14605

Tsk difference between 20 UTC and 12 UTC averaged from 20 to 22 May 1988 Model Tsk difference; forecast from 19880519 12 UTC Wind speed (m/s) Tsk difference retrieved from GOES-8 (Wu et al. 1999; BAMS, 80, 1127-1138)

Impact of the Ocean Slab Model PC1 PC2 Coupled+slab model Mixed-layer model Coupled

Evolution of SST anomalies. 5-day means Control Coupled Coupled + Slab Analysis pentad2-pentad1 pentad3-pentad2 pentad4-pentad3 pentad5-pentad4 pentad6-pentad5

Impact of changes in model parameterization OLR- Forecast range: day 15 ERA40 28R3 29R1 31R1 32R2 32R3 29/12 05/01 12/01 days 20/01 28/01 04/04 12/02 10/04 04/05 09/06 06/07 11/07

Amplitude of the MJO PC1 PC2 28R3 29R1 30R2 31r1 32r2 32r3

MJO Propagation PC1 PC2 28R3 29R1 30R2 31r1 32r2 32r3

CY32R3: velocity Potential at 200hPa Starting date: 29/12/1992

Recent or planned changes to the ECMWF physical parametrizations Improved treatment of ice sedimentation, auto- conversion to snow in cloud scheme and super-saturation with respect to ice (CY31R1) Change in the short-wave radiation code (more wavelengths) + McICA MODIS albedo + revised cloud optical properties (CY32R2) New formulation of convective entrainment Variable relaxation timescale for closure Reduction in background free atmosphere vertical diffusion (CY32R3)

Impact on relative humidity (RH) climatology 31r1 – 30r1 annual mean difference Largest changes in the tropical upper troposphere

Convection changes to operational massflux scheme New formulation of convective entrainment: Previously linked to moisture convergence – Now more dependent on the relative humidity 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. Midlatitude synoptic variability is also increased and is more realistic.

Composite vertical profile for west pac, JJA Minimum cloud top heights distributions (CloudSat) precipitating clouds Of note: Trimodality (quadra-modal) heights precipitating clouds are deeper than non precipitating clouds non- precip clouds

Average tropical cloud profiles In the Tropics now a tri-modal cloud distribution becomes apparent, with a strong increase in mid-level clouds. CloudSat data will be used to verify these results.

Forecast Biases and Convection Precipitation for DJF against GPCP for different cycles: from 15 year 5 months integrations for 1990-2005. CY31R1 Sep 2006 CY32R2 June 2007 CY32R3 Nov 2007

Tropical variability in wave-number frequency space of OLR (DJFM) Obs (NOAA) 32R1 32R3

MJO Prediction Current system CY32R2 VarEPS/Monthly + CY32R3

Conclusion The current monthly forecasting system has some skill to predict the amplitude of the MJO up to about 14 days. However the amplitude of the MJO is significantly reduced after a few days of forecasts, but this will change after the new model operational implementation on 3 November. Sensitivity experiments: Strong impact of ocean-atmosphere coupling No significant impact when increasing the horizontal resolution to about 80 kilometres Strong sensitivity to changes in the model parameterization, and in particular to the mass flux scheme.