Coupled Data Assimilation at ECMWF - how satellite observation are used in coupled numerical weather prediction

Phil Browne

ECMWF Earth System Assimilation Section, Coupled Assimilation Team

2021-05-26

Thanks to P de Rosnay, H Zuo, T McNally, S Massart, D Fairbairn & many others [email protected], @philip_browne

©ECMWF 2021-05-21 Outline

ECMWF’s Earth system approach for forecasting

About ECMWF Products

Coupled Data Assimilation

Operational Impact of Coupled DA

Future coupled data assimilation developments

Future developments

Coupled Data Assimilation at ECMWF 2 ecmwf earth system approach

Coupled Data Assimilation at ECMWF 3 The ECMWF Earth System

Components of ECMWF’s IFS Earth System. Along with the atmosphere, there are the ocean, wave, sea ice, land surface, snow, and lake models. Coupled Data Assimilation at ECMWF 4 Ensemble forecasting

Coupled Data Assimilation at ECMWF 5 Coupled model components

Atmosphere Integrated Forecast System (IFS) Ocean NEMO Sea ice LIM Waves EC-WAM Land surface HTESSEL Lakes FLake

All components are linked at the subroutine level - no coupler is used

Resolutions are grids may be different depending on the application - interpolation happens within the subroutine calls

Coupled Data Assimilation at ECMWF 6 Outline

ECMWF’s Earth system approach for forecasting

About ECMWF Products

Coupled Data Assimilation

Operational Impact of Coupled DA

Future coupled data assimilation developments

Future developments

Coupled Data Assimilation at ECMWF 7 Components of the Earth System Analyses Coupled Assimilation in ERA5

▶ ERA5: land and waves weakly Atmosphere coupled 4D-Var Sea Ice 3D-Var

Land EKF

Ocean 3D-Var Waves OI

Coupled Data Assimilation at ECMWF 8 Components of the Earth System Analyses Coupled Assimilation in NWP

▶ HRES NWP, EDA Atmosphere 4D-Var Sea Ice 3D-Var

Land EKF

Ocean 3D-Var Waves OI

Coupled Data Assimilation at ECMWF 8 ▶ CERA-SAT with also land-atm weak coupling and full observing system ▶ Hence different coupling strategies are used for the different configurations

Components of the Earth System Analyses Coupled Assimilation in reanalyses and NWP research

▶ CERA-20C: outer loop coupling for Atmosphere atm-ocean, sea ice 4D-Var Sea Ice 3D-Var

Land EKF

Ocean 3D-Var Waves OI

Coupled Data Assimilation at ECMWF 8 ▶ Hence different coupling strategies are used for the different configurations

Components of the Earth System Analyses Coupled Assimilation in reanalyses and NWP research

▶ CERA-20C: outer loop coupling for Atmosphere atm-ocean, sea ice 4D-Var ▶ CERA-SAT with also land-atm weak Sea Ice coupling and full observing system 3D-Var

Land EKF

Ocean 3D-Var Waves OI

Coupled Data Assimilation at ECMWF 8 Components of the Earth System Analyses Coupled Assimilation in reanalyses and NWP research

▶ CERA-20C: outer loop coupling for Atmosphere atm-ocean, sea ice 4D-Var ▶ CERA-SAT with also land-atm weak Sea Ice coupling and full observing system 3D-Var ▶ Hence different coupling strategies Land are used for the different EKF configurations

Ocean 3D-Var Waves OI

Coupled Data Assimilation at ECMWF 8 Outline

ECMWF’s Earth system approach for forecasting

About ECMWF Products

Coupled Data Assimilation

Operational Impact of Coupled DA

Future coupled data assimilation developments

Future developments

Coupled Data Assimilation at ECMWF 9 Note that these are only broad categorisations, they tell you nothing about which terms are coupled.

Coupled DA categories

at a later Weakly coupled analysis assimilation Observations affect the analysis of different components at analysis Strongly coupled time assimilation

Formal definitions are available in Stephen G Penny et al. (2017). Coupled Data Assimilation for Integrated Earth System Analysis and Prediction: Goals, Challenges and Recommendations. Tech. rep. World Meteorological Organisation. URL: https://community.wmo.int/wwrp-publications

Coupled Data Assimilation at ECMWF 10 Coupled DA categories

at a later Weakly coupled analysis assimilation Observations affect the analysis of different components at analysis Strongly coupled time assimilation

Formal definitions are available in Stephen G Penny et al. (2017). Coupled Data Assimilation for Integrated Earth System Analysis and Prediction: Goals, Challenges and Recommendations. Tech. rep. World Meteorological Organisation. URL: https://community.wmo.int/wwrp-publications Note that these are only broad categorisations, they tell you nothing about which terms are coupled.

Coupled Data Assimilation at ECMWF 10 Observations affecting the ocean

▶ All satellite/atmospheric observations as they influence atmospheric state and therefore forcing ▶ Altimetry: ▶ Significant wave height ▶ Sea level anomaly ▶ Sea surface temperature ▶ Sea ice concentration Other satellite derived products are important for verification, such as SSS and SIT

Coupled Data Assimilation at ECMWF 11 Challenges for implementing coupled assimilation for NWP

▶ Observation latency e.g. orbit corrected SLA ▶ SST assimilation e.g. products at different depths, cold skin parameterisation, diurnal cycle within the forward model, etc. ▶ Treatment of boundary conditions for inner loops ▶ Cost/impact on long term drift testing ▶ Analysis quality and biases

Coupled Data Assimilation at ECMWF 12 Different biases in coupled assimilation

As an example we can do an experiment with atmospheric boundary conditions are either coming from ▶ a purely observation based data set (uncoupled assimilation) or ▶ our ocean analysis. Each system has its own bias characteristics, e.g. time lag, method of spreading information to unobserved regions, presence of a dynamical model etc. Blindly swapping from one to the other can easily lead to degradations, however NWP infrastructure very quickly highlights these!

Coupled Data Assimilation at ECMWF 13 ECMWF ocean analysis SST errors

BIAS RMSE

Coupled Data Assimilation at ECMWF 14 Outer loop coupling - SST biases in the gulf stream

Coupled Data Assimilation at ECMWF 15 Outline

ECMWF’s Earth system approach for forecasting

About ECMWF Products

Coupled Data Assimilation

Operational Impact of Coupled DA

Future coupled data assimilation developments

Future developments

Coupled Data Assimilation at ECMWF 16 Operational weakly coupled approach

Similarly to how the wave data assimilation and land data assimilation interacts with the atmosphere, we have implemented a weakly coupled data assimilation system 45R1: 2018 For sea ice concentration 46R1: 2019 For sea surface temperature in the tropics This allows different assimilation window lengths in the ocean and atmosphere, giving longer cut off times for late arriving ocean observations.

Coupled Data Assimilation at ECMWF 17 SST coupling in the tropics only

Coupled Data Assimilation at ECMWF 18 Impact of weakly coupled DA - sea ice in the Baltic Sea

FMI/SMHI chart L3 Obs Uncoupled analysis WCDA analysis ICE CHART 2018-02-17 Iskarta - Jääkartta No. 80

Ice10° type 11°Concentration12° 13°Symbols 14° 15° 16° 17° 18° 19° 20° 21° 22° 23° 24° 25° 26° 27° 28° 29° 30° Istyp Koncentration Symboler Jäätyyppi Peittävyys Merkinnät 25-45 Ice free Jammed brash barrier FREJ POLARIS 66° Isfritt - Stampisvall Kalix TORNIO 66° Avovesi Sohjovyö 25-45 Karlsborg Torneå 35-55 New ice (< 5 cm) Rafted ice URHO Nyis (< 5 cm) 7 - 10/10 Hopskjuten is 35-55 KEMI Ajos 25-45 Uusi jää (< 5 cm) Päällekkäin ajautunut jää LULEÅ x Nilas, grey ice (5-15 cm) Ridged or hummocked ice Farstugrunden Malören Tunn jämn is (5-15 cm) 9 - 10/10 Vallar eller upptornad is ODEN* x x Kemi 1 Ohut tasainen jää (5-15 cm) Ahtautunut tai röykkiöitynyt jää x Rödkallen 15-30 15-30 PITEÅ Oulu 1 KONTIO* Fast ice Strips and patches x x Virpiniemi Fastis 10/10 Strängar av drivis 30-50 x Norströmsgrund Kiintojää Ajojäänauhoja x OULU Nygrån x Falkens grund Hailuoto 65° x Uleåborg 65° Rotten fast ice Floebit, floeberg 35-55 Simpgrund Rutten fastis - Isbumling 30-45 Hauras kiintojää Ahtojää - tai röykkiölautta SKELLEFTEÅ RAAHE OTSO x Open water Fracture Gåsören Nahkiainen x Brahestad Öppet vatten < 1/10 Spricka ATLE x Avovesi Repeämä Bjuröklubb Blackkallen Very open ice Fracture zone x 15-30 Ulkokalla x Mycket spridd drivis 1 - 3/10 Område med sprickor KALAJOKI Hyvin harva ajojää Repeämävyöhyke YMER 15-30 Sikeå 20-35 Open ice Estimated ice edge x 64° Rata Storgr. x 64° 4 - 6/10 Kokkola Spridd drivis Uppskattad iskant UMEÅ Harva ajojää Arvioitu jään reuna 15-30 KOKKOLA x St. F-ägg Karleby Close ice Icebreaker ( * coordinating) Kallan x 7 - 8/10 10-25 Tät drivis Isbrytare ( * coordinerande) x ATLE* x Holmögadd PIETARSAARI Tiheä ajojää Jäänmurtaja ( * koordinaattori) Nordvalen x Jakobstad

o ALE x Valassaaret Very close ice o Water temperature isotherm ( C) 9 - 9+/10 o x Helsingkallan Mycket tät drivis 2 Vattentemperaturisoterm ( C) ÖRNSKÖLDSVIK Sydostbrotten o Hyvin tiheä ajojää Veden lämpötilan tasa-arvokäyrä ( C) x Ångermanälven x Skagsudde Norrskär 30-40 Restrictions to Navigation, FINLAND VAASA Consolidated ice o Mean water temperature Trafikrestriktioner, Finland – Liikennerajoitukset, Suomi 10/10 2,1 Ulvöarna 1° Vasa THETIS Sammanfrusen drivis Ytvattnets medeltemperatur x Port Ice Class Minimum tonnage First day of validity 63° 30-50 0,2° 63° Yhteenjäätynyt ajojää Meriveden pintalämpötilan keskiarvo Strömmingsbådan Hamn Isklass Minsta tonnage Datum för ikraftträdande x Högbonden (1971 - 2000) 10-20 Ice thickness (cm) Satama Jääluokka Minimikantavuus Voimaantulopäivä

x Tornio, Kemi, Oulu IA 4000 2018-02-14 20-40 Istjocklek (cm) HÄRNÖSAND Storkallegrund Raahe, Kalajoki, Kokkola, Jään paksuus (cm) 1° IA 2000 2018-02-12 15-30 15-30 Pietarsaari SUNDSVALL KASKINEN IA, IB 2000 x Vaasa 2018-01-27 Restrictions to Navigation, SWEDEN Kaskö IC, II 3000 0,2° 0,5° Sälgrund Trafikrestriktioner, Sverige – Liikennerajoitukset, Ruotsi x Brämön Kaskinen I, II 2000 2018-01-27 Port Min Ice Class Minimum tonnage First day of validity Kristiinankaupunki, Pori, Rauma, Hamn Minsta Isklass Minsta tonnage Datum för ikraftträdande x 62° Gran x Yttergrund Uusikaupunki, Taalintehdas, Förby, 62° Satama Min Jääluokka Minimikantavuus Voimaantulopäivä 2° I, II 2000 2018-02-12 Merikarvia Koverhar, Inkoo, Kantvik, Helsinki, Karlsborg - Skelleftehamn IA 4000 2018-02-07 Sköldvik HUDIKSVALL 0,5° IA, IB 2000 Holmsund - Örnsköldsvik IB 2000 2018-02-07 Loviisa, Kotka, Hamina 2018-02-10 x Mäntyluoto IC, II 3000 Ångermanälven IB 2000 2018-02-07 5-15 Agö x PORI x IA, IB 2000 Björneborg Sköldvik 2018-02-21 Härnösand - Skutskär II 2000 2018-02-05 Säppi IC, II 3000 Köping - Västerås IC 2000 2018-02-03 SÖDERHAMN 1° 10-20 Blomman x Loviisa, Kotka, Hamina IA, IB 2000 2018-02-21 II 2000 x Östra Mälaren 2018-02-06 Rauma RAUMA IC 1300 Raumo Finnish Transport Agency (Liikennevirasto) 61°Vänern, Trollhätte kanal, II 2000 x Finngrundet 0,7° x Kajakulma 61° 2018-02-07 x Göta älv IC 1300 1° UUSIKAUPUNKI VOIMA* IZMAILOV 0,2° Nystad Isokari x 10-20 HAMINA SANKT-PETERBURGVYBORG Swedish Maritime Administration (Sjöfartsverket) GÄVLE x Björn NAANTALI 15-25 Fredrikshamn LOVIISA Vysotsk 15-25 x Nådendal PORVOO Lovisa KOTKA x Grundkallen Saggö TURKU 5-20 Borgå 5-10 x Åbo Sov. Örskär PrimorskNOVOROSSISKIJ Märket Iniö SALO HELSINKI x Zap. Understen x MAARIANHAMINA Helsingfors Haapasaari 10-20 Kumlinge Bol. Berezowyi x Mariehamn INKOO x Svartklubben Kantvik KRUZENSTHERN x Ingå x Harmaja Tiiskeri Suursaari OSLO Lohm Seskar Kotlin 15-30 x x Hogland 60° x Kalbådagr. 60° 2° Nötö Helsinki Rodser Kökar HANKO x Porkkala Bol. Tyters Schepelevski x SANKT- Norrtälje x x x Hangö Vaindlo Söderarm 0,7° x 0,4° Mal. Tyters PETERBURG Jussarö Vigrund Västerås Bengtskär 1° x Mohni MUDJUG Svenska Björn Naissaar Ust-Luga 5-12 x x SEMEN DEZHNEV Köping Trälhavet Bogskär 0,6° Loksa Grums Karlstad x 2° Pakri Muuga Kunda 3° x YURI LISIANSKIJ Osmussaar NARVA Kristinehamn x TALLINN Sillamäe x 10-20 STOCKHOLM x Glotovi Larvik Almagrundet x Paldiski x Tärnan Tahkuna x KAPITAN SOROKIN x Åmål 2°x 1,9° 59° x Strömstad x Huvudskär Ristna 59° Otterbäcken x x HAAPSALU x x 2° x x Oxelösund x Landsort Mariestad x 3° 1° Kopparst. x x x x Gustaf Dalén x Norrköping 4° x PÄRNU Uddevalla G.Sandön Lidköping x x x Vilsandi x 2°x Sandsänkan 10-20 Lysekil Vänersborg 1,7° 4° Kihnu x x Häradskär 2,4° 1° PROTECTOR 58° 4° x 58° x Fårö Pater Noster x Sörve 5° x Storkläppen x x Kolka Skagen x Västervik Irbenskij Ruhnu

4° x x GÖTEBORG Idö x x Knolls gr. Hirstshals Trubaduren x x x 3° Frederikshavn 3° 2° x Östergarn x VENTSPILS x x Ölands N udde x Mersrags Läsö Oskarshamn x x St. Karlsö x x Fladen x 2,3° 57° x x RIGA 57° Aalborg x x Hoburg x Anholt x Akmenrags x Kalmar x Halmstad

x Hallands Väderö 1° Liepaja Utgrunden x Kullen x Karlskrona Hesselö x Karlshamn Hjälm x Aarhus x x Höganäs x Tunö 3° Ölands S gr. x Helsingborg Åhus 2,8° 56° x 56° x 3° Utklippan Rösnäs x 2° Simrishamn Klaipeda KØBENHAVN Kolding x Malmö 3° x Ystad Romsö Drogden Trelleb. 2,6°

x x Odense x Stevns x Falsterborev Hammaren 4° Total ice concentration (in tenths) S cm F diameter x C = Totaliskoncentration (tiondelar) Rönne 5-10 Jään kokonaispeittävyys (kymmenesosina) 0 - 0 - x 1 new ice 1 < 2 m 2° x 2,2° 4° 55° Mön x Partialconcentration 2 < 10 2 2 - 20 m 55° x CaCbCc = Delkoncentration 3 10 - 30 3 20 - 100 m Rozewie Osittaispeittävyys C 4 10 - 15 4 100 - 500 m x Baltijsk Kaliningrad 5 15 - 30 5 500 m - 2 km x x Fehmarn Belt Arkona Stage of development 6 30 - 200 6 2 - 10 km x 3° x Hel Ca Cb Cc Kiel Darsser Ort Gdynia SaSbSc = Istjocklek 7 30 - 70 7 > 10 km x Gedser x Ustka Jään paksuus 8 30 - 50 8 fast ice x Sa Sb Sc Darlowo 9 50 - 70 Gdansk Tolkmicko Form of ice / floesize 1. 70 - 120 x x Fa Fb Fc 1,8° x 2° FaFbFc = Form av is / flakstorlek Kiel Ruden Kolobrzeg Jään muoto / lauttakoko Warnemünde 54° Swinoujscie a b c 54° Travemünde Thickest ice Second thickest ice Third thickest ice Wismar Grövsta isen Näst grövsta isen Tredje grövsta isen Paksuin jää Toiseksi paksuin jää Kolmanneksi paksuin jää Szczecin

10° 11° 12° 13° 14° 15° 16° 17° 18° 19° 20° 21° 22° 23° 24° 25° 26° 27° 28° 29° 30°

Vessels bound for Gulf of Bothnia ports in which traffic restrictions apply shall, when passing the latitude Fartyg destinerade till hamnar med trafikrestriktion i Bottniska viken ska, vid passage av latituden 60°00'N, Aluksen, joka on matkalla Pohjanlahden satamaan, jossa on voimassa liikennerajoitus, on ylittäessään 60°00'N, report their nationality, name, port of destination, ETA and speed to ICE INFO on VHF channel 78. This rapportera enligt instruktionerna för vintersjöfarten till ICE INFO på VHF-kanal 78 eller per telefon +46 31 699 leveysasteen 60°00'N tehtävä talviliikenneohjeen mukainen ilmoitus ICE INFO:lle VHF-kanavalla 78 tai report can also be given directly by phone +46 31 699 100. 100. puhelimitse +46 31 699 100.

Vessels bound for ports in the Bay of Bothnia shall report to Bothnia VTS on VHF channel 67 20 NM before Fartyg destinerade till hamnar i Bottenviken ska 20 nautiska mil före Nordvalen rapportera till Bothnia VTS på Aluksen, joka on matkalla Perämeren satamaan, on 20 mpk ennen Nordvalenin majakkaa ilmoittauduttava Nordvalen lighthouse. VHF-kanal 67. Bothnia VTS:lle VHF-kanavalla 67.

The traffic separation schemes in the Quark are temporarily out of use from 25.01.2018. Trafiksepareringssystemen i Norra Kvarken är tillfälligt ur bruk från 2018-01-25. Reittijakojärjestelmät Merenkurkussa ovat tilapäisesti poissa käytöstä 25.1.2018 alkaen.

The transit traffic west of Holmoarna is temporarily prohibited.arna is temporarily prohibited Transittrafiken väster om Holmöarna är tillfälligt förbjuden. Kauttakulkuliikenne Holmöarnan länsipuolitse on tilapäisesti kielletty.

© FMI & SMHI ISSN: 1796-0185

Sea ice concentrations in the Baltic sea on 20180217. [FMI et al. 2018]

Coupled Data Assimilation at ECMWF 19 Impact of weakly coupled DA - spatial maps

Coupled Data Assimilation at ECMWF 20 Impact of weakly coupled DA - impact with height

RMSE T RMSE R

Browne et al. 2019

Coupled Data Assimilation at ECMWF 21 Outline

ECMWF’s Earth system approach for forecasting

About ECMWF Products

Coupled Data Assimilation

Operational Impact of Coupled DA

Future coupled data assimilation developments

Future developments

Coupled Data Assimilation at ECMWF 22 General developments for coupled ocean-atmosphere DA

▶ Replace atmosphere only model with the coupled model within 4DVar ▶ Combine our outer loop coupling with our weakly coupled system ▶ Introduce coupled observation operators ▶ Pass more information from the atmosphere to the ocean for skin temperature analysis

Coupled Data Assimilation at ECMWF 23 Towards Radiance Assimilation Directly Modifying the Ocean State Using an Augmented Control Variable in the IFS (Massart et al. 2020)

Coupled Data Assimilation at ECMWF 24 Towards Radiance Assimilation Directly Modifying the Ocean State Observation space coupling

Coupled Data Assimilation at ECMWF 25 Towards Radiance Assimilation Directly Modifying the Ocean State Observation space coupling

Coupled Data Assimilation at ECMWF 25 Towards Radiance Assimilation Directly Modifying the Ocean State Observation space coupling

Coupled Data Assimilation at ECMWF 25 Towards Radiance Assimilation Directly Modifying the Ocean State Observation space coupling

Coupled Data Assimilation at ECMWF 25 Outline

ECMWF’s Earth system approach for forecasting

About ECMWF Products

Coupled Data Assimilation

Operational Impact of Coupled DA

Future coupled data assimilation developments

Future developments

Coupled Data Assimilation at ECMWF 26 Future developments

▶ Upgrade of ocean/sea ice model ▶ Move to assimilation of L3/L2 sea ice concentration ▶ Multicategory sea ice model will allow assimilation of SIT from L-band and altimetry (see Balan-Sarojini et al. 2021 for potential impact) ▶ Continuing improvements to radiative transfer codes and emissivity models ▶ Further exploitation of current and future satellite missions ▶ Extend our satellite observation usage to targetted SST sensitive instruments, e.g. SLSTR

Coupled Data Assimilation at ECMWF 27 References

Balan-Sarojini, Beena et al. (2021). “Year-round impact of winter sea ice thickness observations on seasonal forecasts”. In: Cryosphere 15.1, pp. 325–344. ISSN: 19940424. DOI: 10.5194/tc-15-325-2021. Browne, Philip A et al. (2019). “Weakly Coupled Ocean-Atmosphere Data Assimilation in the ECMWF NWP System”. In: Remote Sensing 11.234, pp. 1–24. DOI: 10.3390/rs11030234. FMI et al. (2018). Baltic sea ice chart. URL: http://cdn.fmi.fi/marine-observations/products/ice- charts/20180217-full-color-ice-chart.pdf (visited on 07/10/2018). Massart, S et al. (2020). “Skin temperature analysis for the assimilation of clear-sky satellite radiances”. In: ECMWF Technical Memoranda 870. DOI: 10.21957/goe0ads8z. URL: https://www.ecmwf.int/node/19723. Penny, Stephen G et al. (2017). Coupled Data Assimilation for Integrated Earth System Analysis and Prediction: Goals, Challenges and Recommendations. Tech. rep. World Meteorological Organisation. URL: https://community.wmo.int/wwrp-publications.

Coupled Data Assimilation at ECMWF 28 Backup slides Towards Radiance Assimilation Directly Modifying the Ocean State Using an Augmented Control Variable in the IFS (Massart et al. 2020)

Coupled Data Assimilation at ECMWF 30 Towards Radiance Assimilation Directly Modifying the Ocean State Using an Augmented Control Variable in the IFS (Massart et al. 2020)

Coupled Data Assimilation at ECMWF 30 Towards Radiance Assimilation Directly Modifying the Ocean State Using an Augmented Control Variable in the IFS (Massart et al. 2020)

Coupled Data Assimilation at ECMWF 30 Towards Radiance Assimilation Directly Modifying the Ocean State Using an Augmented Control Variable in the IFS (Massart et al. 2020)

Coupled Data Assimilation at ECMWF 30 Towards Radiance Assimilation Directly Modifying the Ocean State Using an Augmented Control Variable in the IFS (Massart et al. 2020)

Coupled Data Assimilation at ECMWF 30 Towards Radiance Assimilation Directly Modifying the Ocean State Using an Augmented Control Variable in the IFS (Massart et al. 2020)

Coupled Data Assimilation at ECMWF 30 Towards Radiance Assimilation Directly Modifying the Ocean State Using an Augmented Control Variable in the IFS (Massart et al. 2020)

Coupled Data Assimilation at ECMWF 30