Projet de re-prévisions des ensembles globaux : comment refaire le passé pour améliorer le futur....

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

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

• 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

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

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 RévisionsPrévisions rétrospectives

Prévisions historiquesPrévisions 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. ;-)

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.)

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!

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.

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.

Example of perturbations of temperature at 850 hPa (C)

Example of perturbations of winds at 250 hPa (knots)

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.

Current MSC operational reforecast with GEPS• Since December 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, 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 1995-1997, tuesdays 1998-2000, on wednesdays,2001-2004, etc.

An 4 décembre

Décembre…

11 décembre

Décembre...

14 décembre

15 décembre

16 décembre

17 décembre

18 décembre

19 décembre

20 décembre

Décembre …

25 décembre

Décembre/Janvier…

1er janvier

2012 4 mem

4 mem - - - 4 mem - - 4 mem 4 mem

2011 4 mem

4 mem - - - 4 mem - - 4 mem 4 mem

… 4 mem

4 mem - - - 4 mem - - 4 mem 4 mem

1995 4 mem

4 mem - - - 4 mem - - 4 mem 4 mem

Ces dates sont mises en commun pour calculer les statistiques du GEPS (donne 360 cas)

...pour les prévisions de cette semaine

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.).

No. Convection Forçage onde de gravité

Longueur de mélange

Diffusion Verticale

Blocage orographique

Rétro-diffusion

Physique stochastique

0 Kain&Fritsch Standard Bougeault 1.0 1.0 Non Non

1 Kain&Fritsch Fort Blackadar 1.0 1.5 Oui Oui

2 OldKuo Fort Blackadar 1.0 0.5 Oui Oui

3 Kain&Fritsch Faible Bougeault 0.85 0.5 Oui Oui

4 OldKuo Faible Bougeault 0.85 0.5 Oui Oui

5 Kain&Fritsch Faible Blackadar 1.0 1.5 Oui Oui

6 OldKuo Faible Blackadar 1.0 0.5 Oui Oui



9 Kain&Fritsch Fort Bougeault 1.0 1.5 Oui Oui

10 OldKuo Fort Bougeault 1.0 0.5 Oui Oui

11 Kain&Fritsch Fort Bougeault 0.85 1.5 Oui Oui

12 OldKuo Fort Bougeault 0.85 0.5 Oui Oui

13 Kain&Fritsch Faible Blackadar 0.85 1.5 Oui Oui

14 OldKuo Faible Blackadar 0.85 0.5 Oui Oui







SPE canadien – prévisions – SGPE 3.1.01995 1996 1997

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 2011.

• 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 2011. 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).

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

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

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

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

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!

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.

Deep soil moisture difference with CMC analysis (July 4th 2011)

Too dry!

Deep soil temperature difference with CMC analysis (July 4th 2011)

Too warm!

Snow difference with CMC analysis(July 4th 2011)

With CMC sfc analyses

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 3.1.0

T2m

ES2m

T2m

Too dry!

Too warm!

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.

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.

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.

MSLPPCP>10mm in NH

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.

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.

(0.75o) Atmospheric ForcingAir Temp., Winds, Humidity, Precip., Solar/Infrared Radiation

(50 km) Surface & Near Surface 2D FieldsGround Temp, Soil Moisture, Screen-level Winds, Humidity and Temp., Snow Depth etc.

AtmosphericDynamics

SurfacePhysics

GeophysicalDatabases

ERA-interim

40m Winds + Temp. Downward Solar Radiation

Elevation

Veg. Type & Pavement

frac.

SPSScreen-level temp. & winds

(50 km) Land Surface CharacteristicsElevation, Land Cover, Roughness, etc.Abrahamowicz (2014)

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).

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)

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.

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 2011. All forecast were done with GEPS4.0.0 only the initilization differs.

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

GEPS4.0.0-1

T850

Z500


U250

GEPS3.1.0

V850

GEPS4.0.0-1

U250

V850


ES 2m

GEPS3.1.0

T 2m

GEPS4.0.0-1

ES 2m

T 2m


MSLP

GEPS3.1.0

UV at 10m

GEPS4.0.0-1

MSLP

UV at 10m

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

GEPS4.0.0-1

PCP at 24 h

PCP>10mm

On the importance of details of the ISBA scheme

• Even with SPS, the soil still too dry.

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

Sable(%)J1

Argile(%)J2

Wilt

Fc

Sat

+

-

+

-

60%

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

…and cooler


T850

GEPS3.1.0

Z500

GEPS4.0.0-1

T850

Z500


T850

GEPS3.1.0

Z500

GEPS4.0.0

T850

Z500

With modifications to soil capacities and reduction of perturbations


U250

GEPS3.1.0

V850

GEPS4.0.0-1

U250

V850


U250

GEPS3.1.0

V850

GEPS4.0.0

U250

V850



ES 2m

GEPS3.1.0

T 2m

GEPS4.0.0-1

ES 2m

T 2m


ES 2m

GEPS3.1.0

T 2m

GEPS4.0.0

ES 2m

T 2m


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 2mToo warm!


Not cold enough!

Still too dry!


MSLP

GEPS3.1.0

UV at 10m

GEPS4.0.0

MSLP

UV at 10m


PCP at 24h

GEPS3.1.0

PCP>10mm

GEPS4.0.0

PCP at 24 h

PCP>10mm

Concluding remarks

• A improved version of the GEPS reforecasts will include:– GEPS 4.0.0 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…

Difference between precipitation from ERA-int and CMC analyses in the week of August 26 2011

Global average, ERA-interim = 12.5 mm , CMC analyses = 18.5 mm

Cost of reforecast

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).

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.).

Resources on IBM

Requires during 1.25h 12 x 64 cpus = 768 cpus

Scores hiver 2011

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



U250

GEPS3.1.0

V850

GEPS4.0.0

U250

V850



MSLP

GEPS3.1.0

UV at 10m

GEPS4.0.0

MSLP

UV at 10m



ES 2m

GEPS3.1.0

T 2m

GEPS4.0.0

ES 2m

T 2m


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

GEPS4.0.0ES 2m

T 2mToo cold!


Not cold enough!

Not wet enough!

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


Higher resolution ERA-interim fields

Impact of higher resolution ERA-int on RMSE/Spread in N.H. for Summer 2011

T850Z500

U250 V850

Impact of higher resolution ERA-int on RMSE/Spread in N.H. for Summer 2011

ES 2m T2m

UV at 10mMSLP

Impact of higher resolution ERA-int on BSS of 24 h PCP fcst in N.H. for Summer 2011

PCP at 24hin Tropics

PCP>10mm in Tropics

PCP>10mm in NH

PCP at 24hin NH

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.

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

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

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

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 3.1.0 surface fields and CMC analyses.

Impact of starting point on deep soil moisture

AustraliaTexas

Calgary Montréal

Jan2010 Jan2011 Aug2011Jan2010 Jan2011 Aug2011

Jan2010 Jan2011 Aug2011Jan2010 Jan2011 Aug2011

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.

Projet de re-prévisions des ensembles globaux : comment refaire le passé pour améliorer le futur....

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