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Projet de re-prévisions des ensembles globaux : comment refaire le passé pour améliorer le futur. Normand Gagnon CMC/développement, Service Météorologique.

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Presentation on theme: "Projet de re-prévisions des ensembles globaux : comment refaire le passé pour améliorer le futur. Normand Gagnon CMC/développement, Service Météorologique."— Presentation transcript:

1 Projet de re-prévisions des ensembles globaux : comment refaire le passé pour améliorer le futur. Normand Gagnon CMC/développement, Service Météorologique du Canada Environnement Canada Dorval, Québec, Canada

2 Projet de re-prévisions des ensembles globaux : comment refaire le passé (pour qu’il ressemble au présent) pour améliorer le futur. Normand Gagnon CMC/développement, Service Météorologique du Canada Environnement Canada Dorval, Québec, Canada

3 Maria Abrahamowicz has helped me a lot with SPS (preparation of the suite, etc.). Ryan Muncaster has run the SPS over 30 years. Bernard Dugas has provided surface fields for the current operational reforecasts. Katja Winger of UQAM has provided us with the forcing to run SPS. She also has given us the ERA-interim reanalyses at higher horizontal resolution. These were prepared by Dominique Paquin of Ouranos. Rochdi Lahlou has built the operational suite. Stéphane Beauregard has developped the statistics module in the reforecast suite. Discussions: Hai Lin, Bertrand Denis, Peter Houtekamer Martin Charron, Benoit Archambault, Juan Sebastian Fontecilla et al. Acknowledgements

4 Plan de la présentation Qu’est-ce que des re-prévisions (‘reforecasts’) ? Pourquoi ? Comment ? Description du système courant Description des améliorations –Mise a jour du GEPS (4.0.0 vs 3.1.0) –Données des Ré-analyses ERA-interim à plus haute résolution –Champs de surface historiques produits par SPS –Réduction des perturbations initiales Resumé

5 Qu’est-ce que des re-prévisions? Vient du terme anglais ‘reforecast’ qui désigne refaire des prévisions pour des dates passées a posteriori avec un système de prévision actuel. On appelle aussi cela ‘hindcast’ ou ‘historical forecasts’. Pour le choix de la traduction, de ‘reforecast’ en re- prévisions, nous avons eu de brillants échanges là- dessus et j’ai choisi re-prévisions mais bon... Rétrovisions Révisions Prévisions rétrospectives Prévisions historiques Prévisions a posteriori Prévisions antérieures Reforecasts! D’ailleurs, je vais animer une vivifiante table-ronde à la grande bibliothèque le 31 novembre prochain, bienvenue à tous. ;-)

6 Reforecasting: motivation We want to do « reforecast » with GEPS mainly to generate: –Climate (average and standard deviation) for monthly forecast (32 days) –Climate for Extreme Forecast Index calculation –Calibration of the forecast probabilities to improve upon member counting –Training of post-processing schemes (MOS, etc.) –Provide database for specialized users (hydrology, agriculture, etc.)

7 Exemple de bénéfices des re-prévisions R. Hagedorn, ECMWF Newsletter Fall 2008 More members are helping for longer lead times! More years are helping for all lead times!

8 Oui, mais comment ? Hamill et al. à la NOAA ont fait 2 fois des reforecasts sur 30 ans (11 membres) avec le système GEFS avec succès (Hamill et al. 2013). Par contre, c’était des re- prévisions statiques (fait au complet avec un système gelé). ECMWF fait des re-prévisions depuis plusieurs années aux opérations (5 membres sur 20 ans) en utilisant la technique ‘on-the-fly’. Les dates sont faites aux opérations de façon graduelle. Ceci permet d’avoir des re-prévisions qui sont fait avec ‘exactement’ le système opérationnel. Nous avons préféré cette approche car le GEPS change souvent. NCEP étudie cet idée présentement.

9 Current operational reforecast There are no assimilation with Ensemble Kalman Filter (too costly for us to do reanalyses). We start from perturbed upper air re-analyses from ERA- interim (Dee et al. 2011). We used these at 1.5 horizontal degree resolution. The atmospheric perturbations are homogeneous and isotropic as in Gauthier et al. (1999). Only the streamfunction and the unbalanced temperature are perturbed here and in EnKF (see Houtekamer et al.,2009). These perturbations are transformed to wind, temperature and surface pressure.

10 Example of perturbations of temperature at 850 hPa (C)

11 Example of perturbations of winds at 250 hPa (knots)

12 Comment faire sans FKEn? Réanalyses ERA-interim sur 37 niveaux de pressions Interpolation sur les 74 niveaux du modèle du GEPS Perturbations homogènes isotropes pour 4 membres Même module que les prévisions opérationnelles (sauf 4 membres au lieu de 21) Module de calcul des statistiques : moyennes sem., mois, percentiles etc.

13 Current MSC operational reforecast with GEPS Since December 4 th 2013, we are running 4 members over 32 days for 18 years once a week for a given date at CMC operations. For the date of Thursday in 5 weeks, for example, the week of December , we would run the December 18 of the last 18 years (1995 to 2012). This is giving 2 weeks of slack (because the forecasts done during the week of December 4th 2014 will begin to use December 18th reforecast). Also, the load is distributed over 6 days in operations (3 years per day), for exemple on sundays, we are running , tuesdays , on wednesdays, , etc.

14 An 4 décembreDécembre…11 décembre Décembre...14 décembre15 décembre 16 décembre 17 décembre 18 décembre 19 décembre 20 décembre Décembre … 25 décembre Décembre/Janvier…1 er janvier mem mem … mem Ces dates sont mises en commun pour calculer les statistiques du GEPS (donne 360 cas)...pour les prévisions de cette semaine

15 Current operational reforecast Surface fields are initialized with model climate. More specifically, monthly means of a 11-year AMIP run done with the GEM model interpolated to the day of the start of the reforecast. Since we have a multi-physics ensemble, we need to select each flavour of the parameterizations about the same number of times (ex: each 2 convection schemes are selected half of the time). To do so, we select each member in function of the year (for example: in 1995, we run member 1, 6, 11 and 16; in 1996 we run member 2, 7, 12 and 17, etc.).

16 No.ConvectionForçage onde de gravité Longueur de mélange Diffusion Verticale Blocage orographique Rétro- diffusion Physique stochastique 0Kain&FritschStandardBougeault1.0 Non 1Kain&FritschFortBlackadar1.01.5Oui 2OldKuoFortBlackadar1.00.5Oui 3Kain&FritschFaibleBougeault Oui 4OldKuoFaibleBougeault Oui 5Kain&FritschFaibleBlackadar1.01.5Oui 6OldKuoFaibleBlackadar1.00.5Oui 7Kain&FritschFaibleBougeault1.01.5Oui 8OldKuoFaibleBougeault1.00.5Oui 9Kain&FritschFortBougeault1.01.5Oui 10OldKuoFortBougeault1.00.5Oui 11Kain&FritschFortBougeault Oui 12OldKuoFortBougeault Oui 13Kain&FritschFaibleBlackadar Oui 14OldKuoFaibleBlackadar Oui 15Kain&FritschFortBlackadar Oui 16OldKuoFortBlackadar Oui 17Kain&FritschFortBlackadar1.00.5Oui 18OldKuoFortBlackadar1.01.5Oui 19Kain&FritschFaibleBougeault Oui 20OldKuoFaibleBougeault Oui SPE canadien – prévisions – SGPE

17 Testing of the reforecasts quality To evaluate the reforecast quality, we have compared them as if they were used to initialize 15 day forecasts in We are comparing the GEPS3.1.0 official forecasts (as initialized with EnKF) and forecasts started with the reforecasts initialization method in Summer 2011 and Winter All forecasts were done with the GEPS3.1.0 model configurations at 66 km only the initialization differs. Exceptionally, for the comparison, we have used the same ensemble size as the operational forecasts (20).

18 Comparison of initialization EnKF and ERA-int reforecast method for GEPS3.1.0 on RMSE/Spread in N.H. (RAOBS) T850 Summer 2011 Z500 Winter 2011 T850 Z500

19 Comparison of initialization EnKF and ERA-int reforecast method for GEPS3.1.0 on RMSE/Spread in N.H. (RAOBS) U250 Summer 2011 V850 Winter 2011 U250 V850

20 Comparison of initialization EnKF and ERA-int reforecast method for GEPS3.1.0 on RMSE/Spread in N.H. (SYNOP stations) MSLP Summer 2011 UV10m Winter 2011 MSLP UV10m

21 But, for T2m and ES2m ….Comparison of initialization EnKF and ERA-int reforecast method for GEPS3.1.0 on RMSE/Spread in N.H. ES 2m Summer 2011 T 2m Winter 2011 ES 2m T 2m

22 Comparison of initialization EnKF and ERA-int reforecast method for GEPS3.1.0 on Bias in N.H. ES2m Summer 2011 T2m Winter 2011 ES2m T2m Too dry! Too warm!

23 Conclusion from the first version of the reforecast procedure The atmospheric perturbations added to ERA-interim re- analyses are working relatively well to simulate EnKF quality (loss of 6-24h of predictability). There is slightly more spread created by the isotropic homogenous perturbations than by the EnKF system. There is a major problem with the surface.

24 Deep soil moisture difference with CMC analysis (July 4 th 2011) Too dry!

25 Deep soil temperature difference with CMC analysis (July 4 th 2011) Too warm!

26 Snow difference with CMC analysis (July 4 th 2011)

27 With CMC sfc analyses Proof: if we run forecasts in 2011 initialized ‘a la reforecast’ but in taking the CMC surface analyses instead of the climate fields from the AMIP run. ES2m GEPS T2m ES2m T2m Too dry! Too warm!

28 So problems at the surface AMIP type run relatively free model run (not attached to current condition except SST). Surface fields not adapted to the model grid (lower resolution). Also no interannual variability because always same surface fields at a given date.

29 Improvements to the reforecast procedure: upgrade of the GEPS 1) upgrade of the GEPS (4.0.0 vs 3.1.0) which includes: –More recent GEM model (4.6.0 vs 4.4.5) –Higher horizontal (50 km vs 66 km) and temporal (15 min vs 20 min) resolution –Sea-ice now evolves along the run (using thresholds on SST). –Perturbation of parameters for salty water, diffusion on Theta –There is generally a gain of predictability of 6 hour for most upper air fields while this improvement is larger at the surface and for the precipitation.

30 Improvements: higher resolution version of the reanalyses 2) The reanalyses ERA-interim (Dee et al. 2011) have been produced on a 0.75 degree grid. In our first version of the reforecast, we were using fields on a 1.5 degrees grid. MSLP PCP>10mm in NH

31 Impact of higher resolution of reanalyses Small positive impact (short range) except on mean sea level pressure and precipitation which are significantly improved during week 1.

32 Improvements: SPS fields 3) In our first version of the reforecasts, we were simply interpolating fields from a climate of the GEM model in AMIP set-up. Now, instead, we will run the Surface Prediction System in the past to generate surface fields compatible with the surface scheme of the model. This system is simply the surface schemes of the GEM model used in offline mode forced by near-surface atmospheric fields.

33 (0.75 o ) Atmospheric Forcing Air Temp., Winds, Humidity, Precip., Solar/Infrared Radiation ( 50 km ) Surface & Near Surface 2D Fields Ground Temp, Soil Moisture, Screen-level Winds, Humidity and Temp., Snow Depth etc. Atmospheric Dynamics Surface Physics Geophysical Databases ERA-interim 40m Winds + Temp. Downward Solar Radiation Elevation Veg. Type & Pavement frac. SPS Screen-level temp. & winds (50 km) Land Surface Characteristics Elevation, Land Cover, Roughness, etc. Abrahamowicz (2014)

34 SPS includes: ISBA land scheme operational since 2001 at CMC based on Noilhan and Planton (1989) –2 layers in the soil (layer 1 = first 10 cm, layer 2 = root zone below this ) –Follow force-restore like equations Simple glacier scheme Simple sea-ice scheme Each grid point is independent (no horizontal exchange).

35 SPS configuration Run 30 years forced by ERA-interim at 2m (10m) to cover the reforecast period ( ) and more. It includes 2 years of spin-up. Same grid as the GEPS (50 km, 800x400) Initial condition from CMC surface analyses SPS time step: 30 minutes Fields provided to SPS: Temperature and relative humidity at 2m, wind components at 10m, radiative fluxes (incoming solar and infra-red radiation) and hourly precipitation amount. Frequency: every 3 hour (interpolated at every time step)

36 SPS configuration Temperature is adjusted for difference in elevation between ERA-interim topography and GEM model one (via lapse rate of 6.5C/km). Please note that relative humidity is kept constant, therefore, specific humidity is adjusted.

37 Testing of the impact of SPS fields on atmospheric reforecasts The SPS fields were used to do 15 day forecasts. It has to be noted that the comparison includes change to GEPS4.0.0 also (50 km, higher resolution ERA- interim, etc.). We are comparing the GEPS4.0.0 forecasts (as initialized with EnKF) and the reforecasts initialization method in Summer All forecast were done with GEPS4.0.0 only the initilization differs.

38 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on RMSE/Spread in N.H. for Summer 2011 T850 GEPS3.1.0 Z500 GEPS T850 Z500

39 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on RMSE/Spread in N.H. for Summer 2011 U250 GEPS3.1.0 V850 GEPS U250 V850

40 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on RMSE/Spread in N.H. for Summer 2011 ES 2m GEPS3.1.0 T 2m GEPS ES 2m T 2m

41 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on RMSE/Spread in N.H. for Summer 2011 MSLP GEPS3.1.0 UV at 10m GEPS MSLP UV at 10m

42 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on BSS in N.H. for Summer 2011 PCP at 24h GEPS3.1.0 PCP>10mm GEPS PCP at 24 h PCP>10mm

43 On the importance of details of the ISBA scheme Even with SPS, the soil still too dry.

44 Modifications to SPS land properties Instead of using a relationship with sand and clay proportions in the soil to determine saturation soil moisture, the wilting point and the field capacity, we have changed these limits to constant values (from Maria and Shunli) that leads to better match with observations: Wsat Wwilt Wfc

45 Sable(%) J1 Argile(%) J2 Wilt Fc Sat %

46 Impact is important: soil becomes generally much wetter (difference after 18 months runs on July )

47 …and cooler

48 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on RMSE/Spread in N.H. for Summer 2011 T850 GEPS3.1.0 Z500 GEPS T850 Z500

49 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on RMSE/Spread in N.H. for Summer 2011 T850 GEPS3.1.0 Z500 GEPS4.0.0 T850 Z500 With modifications to soil capacities and reduction of perturbations

50 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on RMSE/Spread in N.H. for Summer 2011 U250 GEPS3.1.0 V850 GEPS U250 V850

51 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on RMSE/Spread in N.H. for Summer 2011 U250 GEPS3.1.0 V850 GEPS4.0.0 U250 V850 With modifications to soil capacities and reduction of perturbations

52 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on RMSE/Spread in N.H. for Summer 2011 ES 2m GEPS3.1.0 T 2m GEPS ES 2m T 2m

53 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on RMSE/Spread in N.H. for Summer 2011 ES 2m GEPS3.1.0 T 2m GEPS4.0.0 ES 2m T 2m With modifications to soil capacities and reduction of perturbations

54 Too dry! Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on Bias in N.H. for Summer 2011 ES 2m GEPS3.1.0 T 2m GEPS4.0.0 ES 2m T 2m Too warm! With modifications to soil capacities and reduction of perturbations Not cold enough! Still too dry!

55 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on RMSE/Spread in N.H. for Summer 2011 MSLP GEPS3.1.0 UV at 10m GEPS4.0.0 MSLP UV at 10m

56 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on RMSE/Spread in N.H. for Summer 2011 MSLP GEPS3.1.0 UV at 10m GEPS4.0.0 MSLP UV at 10m With modifications to soil capacities and reduction of perturbations

57 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on BSS in N.H. for Summer 2011 PCP at 24h GEPS3.1.0 PCP>10mm GEPS4.0.0 PCP at 24 h PCP>10mm

58 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on BSS in N.H. for Summer 2011 PCP at 24h GEPS3.1.0 PCP>10mm GEPS4.0.0 PCP at 24 h PCP>10mm With modifications to soil capacities and reduction of perturbations

59 Concluding remarks A improved version of the GEPS reforecasts will include: –GEPS configuration (50 km, etc.) –Higher resolution re-analyses –Surface fields coming from a 20 year run of SPS –Reduction of the atmospheric perturbations This is version leads to a much better match with operational forecasts for all fields. Still some work to do on ES2m and T2m. We might need to adjust the forcings (precipitation) or nudging or pseudo-analysis…

60 Difference between precipitation from ERA-int and CMC analyses in the week of August Global average, ERA-interim = 12.5 mm, CMC analyses = 18.5 mm

61 Bonus

62 Cost of reforecast

63 Estimated cost 4 members X 18 years = 72 reforecasts of 32 days We will do these integrations on 6 days (no reforecast done on Thursday because the monthly forecast will be done that day). To be symmetric, we propose 72 reforecasts over 6 days a week so 12 reforecasts (3 dates x 4 members) of 32 days to be done during low traffic hours on the supercomputer. This equivalent to around 46% of the total cost of the GEPS forecasts (including monthly forecast).

64 Estimated cost The set of output fields will be greatly reduced from what we used to store. We will keep on disk mainly PDF stats (percentile, etc.).

65 Resources on IBM Requires during 1.25h 12 x 64 cpus = 768 cpus

66 Scores hiver 2011

67 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on RMSE/Spread in N.H. for Winter 2011 T850 GEPS3.1.0 Z500 GEPS4.0.0 T850 Z500 With modifications to soil capacities and reduction of perturbations

68 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on RMSE/Spread in N.H. for Winter 2011 U250 GEPS3.1.0 V850 GEPS4.0.0 U250 V850 With modifications to soil capacities and reduction of perturbations

69 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on RMSE/Spread in N.H. for Winter 2011 MSLP GEPS3.1.0 UV at 10m GEPS4.0.0 MSLP UV at 10m With modifications to soil capacities and reduction of perturbations

70 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on RMSE/Spread in N.H. for Winter 2011 ES 2m GEPS3.1.0 T 2m GEPS4.0.0 ES 2m T 2m With modifications to soil capacities and reduction of perturbations

71 Too wet! Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on Bias in N.H. for Summer 2011 ES 2m GEPS3.1.0 T 2m GEPS4.0.0 ES 2m T 2m Too cold! With modifications to soil capacities and reduction of perturbations Not cold enough! Not wet enough!

72 Comparison of initialization EnKF and ERA-int reforecast method for GEPS4.0.0 and GEPS3.1.0 on BSS in N.H. for Winter 2011 PCP at 24h GEPS3.1.0 PCP>10mm GEPS4.0.0 PCP at 24 h PCP>10mm With modifications to soil capacities and reduction of perturbations

73 Higher resolution ERA-interim fields

74 Impact of higher resolution ERA-int on RMSE/Spread in N.H. for Summer 2011 T850 Z500 U250 V850

75 Impact of higher resolution ERA-int on RMSE/Spread in N.H. for Summer 2011 ES 2m T2m UV at 10m MSLP

76 Impact of higher resolution ERA-int on BSS of 24 h PCP fcst in N.H. for Summer 2011 PCP at 24h in Tropics PCP>10mm in Tropics PCP>10mm in NH PCP at 24h in NH

77 Improvements: reduction of the perturbations 4) To create different analyses, homogeneous isotropic perturbations are added to the ERA-interim re- analysed values. The magnitude of these initial perturbations were reduced to try to better match the operational level of spread.

78 Comparison reduce perturbations (covar=0.8) on RMSE/Spread in N.H. for Summer 2011 T850 Covar = 1.0 Z500 Covar = 0.8 T850 Z500

79 Comparison of reduce perturbations (covar=0.8) on RMSE/Spread in N.H. for Summer 2011 U250 Covar = 1.0 V850 Covar = 0.8 U250 V850

80 Comparison reduce perturbations (covar=0.8) on RMSE/Spread in N.H. for Summer 2011 ES 2m Covar = 1.0 T 2m Covar = 0.8 ES 2m T 2m

81 On the importance of the starting point… One might ask if the date at which we start to cycle SPS is important. Ryan is suggesting 2 years of spin-up based on another similar experiment with the more sophisticated CLASS scheme. We have started on January 1st 2010 with 2 different analyses: GEPS surface fields and CMC analyses.

82 Impact of starting point on deep soil moisture Australia Texas Calgary Montréal Jan2010 Jan2011 Aug2011

83 Impact of starting point In SPS: – Little impact on soil temperature in both layers past 6 months. –Soil moisture near surface is also converging rapidly –Deep soil moisture and snow mass can take more than 1.5 years to converge. –Of course, for points with difference in land-sea mask or glacier mask the delay of adjustment can be longer.


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