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Normand Gagnon CMC/développement, Service Météorologique du Canada Environnement Canada

This project delves into the significance of historical reforecasts or hindcasts to improve future predictions. Normand Gagnon highlights the process of re-forecasting past weather scenarios with updated predictive models to enhance forecast accuracy. The use of advanced techniques and updated data sources like ERA-interim reanalyses aids in refining the Global Ensemble Prediction System (GEPS). Reforecasts enable the calculation of climate averages, extreme indices, and probability calibrations necessary for better forecast outcomes. This innovative approach offers various benefits across different sectors, such as hydrology and agriculture. Through insightful examples and practical applications, this project showcases how historical forecasts can shape and elevate future meteorological predictions.

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Normand Gagnon CMC/développement, Service Météorologique du Canada Environnement Canada

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  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. Acknowledgements • 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 currentoperationalreforecasts. Katja Winger of UQAM has provided us with the forcing to run SPS. Shealso has givenus the ERA-interimreanalysesathigher horizontal resolution. Thesewereprepared 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.

  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 ‘historicalforecasts’. • 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... Reforecasts! D’ailleurs, je vais animer une vivifiante table-ronde à la grande bibliothèque le 31 novembre prochain, bienvenue à tous. ;-) Prévisions antérieures Prévisions rétrospectives Prévisions a posteriori Révisions Rétrovisions Prévisions historiques

  6. Reforecasting: motivation • Wewant to do « reforecast » with GEPS mainly to generate: • Climate (average and standard deviation) for monthlyforecast (32 days) • Climate for ExtremeForecast Index calculation • Calibration of the forecastprobabilities to improveuponmembercounting • Training of post-processingschemes (MOS, etc.) • Providedatabase for specializedusers (hydrology, agriculture, etc.)

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

  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 (toocostly for us to do reanalyses). • Westartfromperturbedupper air re-analyses from ERA-interim (Dee et al. 2011). Weusedtheseat 1.5 horizontal degreeresolution. The atmospheric perturbations are homogeneous and isotropic as in Gauthier et al. (1999). Only the streamfunction and the unbalancedtemperature are perturbedhere 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 operationalreforecastwith GEPS • SinceDecember 4th 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 18 2014, wewouldrun the December 18 of the last 18 years (1995 to 2012). • This isgiving 2 weeks of slack (because the forecastsdoneduring the week of December 4th 2014 willbegin to use December 18th reforecast). • Also, the loadisdistributed over 6 days in operations (3 years per day), for exemple on sundays, we are running 1995-1997, tuesdays 1998-2000, on wednesdays,2001-2004, etc.

  14. 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 initializedwith model climate. More specifically, monthlymeans of a 11-year AMIP rundonewith the GEM model interpolated to the day of the start of the reforecast. Sincewe have a multi-physics ensemble, weneed to select eachflavour of the parameterizations about the samenumber of times (ex: each 2 convection schemes are selectedhalf of the time). To do so, we select eachmember in function of the year (for example: in 1995, werunmember 1, 6, 11and 16; in 1996 werunmember2, 7, 12and 17, etc.).

  16. 1995 1996 1997 SPE canadien – prévisions – SGPE 3.1.0

  17. Testing of the reforecasts quality • To evaluate the reforecastquality, we have comparedthem as if theywereused to initialize 15 dayforecasts in 2011. • We are comparing the GEPS3.1.0 official forecasts (as initializedwith EnKF) and forecastsstartedwith the reforecastsinitializationmethod in Summer 2011 and Winter 2011. All forecastsweredonewith the GEPS3.1.0 model configurations at 66 km only the initializationdiffers. • Exceptionally, for the comparison, we have used the same ensemble size as the operationalforecasts (20).

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

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

  20. Comparison of initialization EnKF and ERA-int reforecast method for GEPS3.1.0 on RMSE/Spread in N.H. (SYNOP stations) Summer 2011 Winter 2011 MSLP MSLP UV10m 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. Summer 2011 Winter 2011 ES 2m ES 2m T 2m T 2m

  22. Comparison of initialization EnKF and ERA-int reforecast method for GEPS3.1.0 on Bias in N.H. Winter 2011 Summer 2011 ES2m ES2m Too dry! T2m T2m 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 4th 2011) Too dry!

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

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

  27. 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. GEPS 3.1.0 ES2m ES2m Too dry! With CMC sfc analyses T2m With CMC sfc analyses T2m 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 reforecastprocedure: 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: higherresolution 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. PCP>10mm in NH MSLP

  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. Atmospheric Dynamics (0.75o) Atmospheric Forcing Air Temp., Winds, Humidity, Precip., Solar/Infrared Radiation ERA-interim 40m Winds + Temp. Downward Solar Radiation SPS Surface Physics (50 km) Surface & Near Surface 2D Fields Ground Temp, Soil Moisture, Screen-level Winds, Humidity and Temp., Snow Depth etc. Screen-level temp. & winds Veg. Type & Pavement frac. Elevation (50 km) Land Surface Characteristics Elevation, Land Cover, Roughness, etc. Geophysical Databases 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 (1995-2012) 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 SPSfields on atmosphericreforecasts • 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 2011. 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 GEPS3.1.0 GEPS4.0.0-1 T850 T850 Z500 Z500

  39. Comparison of initialization EnKF and ERA-intreforecastmethod for GEPS4.0.0 and GEPS3.1.0 on RMSE/Spread in N.H. for Summer 2011 GEPS3.1.0 GEPS4.0.0-1 U250 U250 V850 V850

  40. Comparison of initialization EnKF and ERA-intreforecastmethod for GEPS4.0.0 and GEPS3.1.0 on RMSE/Spread in N.H. for Summer 2011 GEPS3.1.0 GEPS4.0.0-1 ES 2m ES 2m T 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 GEPS3.1.0 GEPS4.0.0-1 MSLP MSLP UV at 10m 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 GEPS4.0.0-1 GEPS3.1.0 PCP at 24h PCP at 24 h PCP>10mm 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: Wfc Wwilt Wsat

  45. - Sable(%) J1 Sat + - Argile(%) J2 Fc + 60% Wilt

  46. Impact is important: soil becomes generally much wetter (difference after 18 months runs on July 2 2011)

  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 GEPS3.1.0 GEPS4.0.0-1 T850 T850 Z500 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 GEPS3.1.0 GEPS4.0.0 T850 T850 With modifications to soil capacities and reduction of perturbations Z500 Z500

  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 GEPS3.1.0 GEPS4.0.0-1 U250 U250 V850 V850

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