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Norihisa USUI, Yosuke Fujii, Kei Sakamoto and Masafumi Kamachi

Improved representation of nearshore processes at the southern coast of Japan using a 4DVAR assimilation system. Norihisa USUI, Yosuke Fujii, Kei Sakamoto and Masafumi Kamachi. (Japan Meteorological Agency/Meteorological Research Institute). GOV COSS-TT workshop @ U of Miami, 10-12 Jan. 2012.

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Norihisa USUI, Yosuke Fujii, Kei Sakamoto and Masafumi Kamachi

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  1. Improved representation of nearshore processes at the southern coast of Japan using a 4DVAR assimilation system Norihisa USUI, Yosuke Fujii, Kei Sakamoto and Masafumi Kamachi (Japan Meteorological Agency/Meteorological Research Institute) GOV COSS-TT workshop @ U of Miami, 10-12 Jan. 2012

  2. Outline • Overview of present operational systems in JMA • Introduction of a next generation coastal system • High-resolution model • 4DVAR assimilation scheme • Development plan of the coastal system • Preliminary results of 4DVAR assimilation system • Summary and future issues

  3. Present operational DA systems in JMA: MOVE/MRI.COM • Global (MOVE/MRI.COM-G) • 75oS – 75oN • 1o x 1o, L50 • Initialization for ENSO and seasonal forecast • North Pacific （MOVE/MRI.COM-NP） • 100oE-75oW, 15oS-65oN • 0.5ox0.5o, L54 • Parent model for WNP model One-way nesting • Western North Pacific • （MOVE/MRI.COM-WNP） • 117oE-160oW, 15oN-65oN • 0.1ox0.1o, L54 • Monitoring and forecasting of ocean state around Japan (SST, Kuroshio, mesoscale eddy, …etc)

  4. Present operational systems in JMA: Ocean model • MRI Community Ocean Model (MRI.COM; Tsujino et al. 2010) • Z-coordinate, free-surface • Quasi-enstrophy conservation scheme • Topography diagonally upward advection scheme (Ishizaki and Motoi 1999)

  5. Present operational systems in JMA: Assimilation scheme • MRI Multivariate Ocean Variational Estimation System • (MOVE; Usui et al. 2006) • 3DVAR with vertical coupled temperature and salinity EOF modes • (Fujii & Kamachi 2003) • Incremental Analysis Updates (Bloom et al. 1996) • Observation: • Along track SSH anomaly • Gridded SST (MGDSST: Japan-GHRSST) • T-S profiles • Sea ice concentration (for MOVE-WNP) 4

  6. Present operational systems in JMA: Assimilation scheme • 3DVAR with vertical coupled T-S EOF modes • Cost function: Deviation from T S observation Deviation from first guess Deviation from altimetry data z: amplitudes of T-S EOF modes (control variables) x: temperature and salinity • Transformation from mode amplitude to T-S fields (z  x) Singular values of T-S EOF T-S EOF modes Standard deviation of the background field 5

  7. Next generation coastal system (MOVE/MRI.COM-Jpn): Purpose • Upgrade the present ocean information • Sea surface temperature • Kuroshio and Oyashio • Sea ice in the sea of Okhotsk • … etc • New targets of the coastal system • “Kyucho” : a sudden and swift current caused by • Small scale disturbances propagating along the Kuroshio (frontal waves) • Coastal waves induced by along-shore winds • “Abiki” : large-amplitude seiches • generated by atmospheric pressure disturbances 6

  8. Next generation coastal system (MOVE/MRI.COM-Jpn): Purpose • “Kyucho” event Isobe et al. (2010) • Formation of “Abiki” Hibiya and Kajiura (1982) 7

  9. Next generation coastal system: High-resolution ocean model MRI.COM-Jpn: WNP model domain • Resolution: 1/33o x 1/50o (~ 2km) • Domain: 117o-167oE, 25o-50oN • Incorporate tidal forcing Jpn model domain 8

  10. Next generation coastal system: Data assimilation Present operational system employs 3DVAR scheme as an assimilation method Computational cost is relatively low. Open ocean mesoscale phenomena such as Kuroshio meanders and mesoscale eddies can be reproduced. • But 3DVAR scheme is not appropriate for high-frequency phenomena in coastal regions Need for a more sophisticated assimilation method 9

  11. Next generation coastal system: Data assimilation MOVE-4DVAR: • Take advantage of experience of the present 3DVAR system • Statistics of the background errors (T-S EOF) • Observation operators • Nonlinear constraints, …etc • A prototype 4DVAR system has been developed using the WNP (0.1x0.1) model • The prototype 4DVAR system will be extended to an incremental 4DVAR system as an assimilation part of the next generation coastal system, MOVE/MRI.COM-Jpn z: amplitudes of T-S EOF modes x: temperature and salinity 10

  12. Next generation coastal system: Time schedule • 2008 • The present system (MOVE/MRI.COM-WNP) was used in operation. • 2014 • The prototype 4DVAR system with the WNP model (1/10o x 1/10o) will be in demonstration phase. • 2017 • MOVE/MRI.COM-Jpn using the incremental 4DVAR scheme will be in operation. • Forward model: MRI.COM-Jpn (1/33o x 1/50o ~ 2km) • Analysis model: MRI.COM-WNP (1/10o x 1/10o ~ 10km) 11

  13. Preliminary results of the prototype 4DVAR assimilation system 12

  14. Backward propagation of adjoint sensitivities Assimilation window: 1-month (Jan 1st – Jan 31st, 2000) Hovmellor diagrams of the adjoint variables along the Kuroshio axis in Jan 2000 13

  15. Warm water intrusion from the Kuroshio into a coastal area 10-Jan-2000 5-Feb-2000 29-Jan-2000 Obs (SST) 3DVAR (5-day window) 4DVAR (10-day window) 14

  16. Sea level anomaly at the southern coast of Japan Location of tide gauge stations 4 3 2 Black: Observation Blue : 3DVAR (5-day window) Red : 4DVAR (10-day window) 1 Sea level anomaly (cm) Sea level anomaly (cm) 1. Tosashimizu 2. Uragami Sea level anomaly (cm) Sea level anomaly (cm) 4. Irozaki 3. Toba 15

  17. Enhancement of temperature variability in the coastal area Difference in subsurface (100m) temperature variability between 3DVAR and 4DVAR 16

  18. Summary (1): 4DVAR results • MRI has been developing a 4DVAR scheme as an assimilation part of the next generation coastal system in JMA. • Results of a prototype 4DVAR system were evaluated focusing on nearshore processes. • A warm water intrusion event caused by a disturbance propagating along the Kuroshio was successfully reproduced by the 4DVAR system. • The 4DVAR system improve high-frequency variability in coastal areas compared with 3DVAR.  The 4DVAR scheme is suitable for the next-generation coastal system. 17

  19. Summary (2): MOVE/MRI.COM-Jpn • System name: MOVE/MRI.COM-Jpn • High-resolution (~2km) coastal model (MRI.COM-Jpn) • Incremental 4DVAR assimilation using the 10km analysis model • Objectives: • Upgrade the present ocean information in the open ocean • Nowcasting and forecasting coastal phenomena • Assessment strategies: • Further evaluation using coastal obs such as tide gauge, buoy and HF radar • Applications: • “Kyucho” and “Abiki (potential)” forecast • Oil spill forecast and rescue activity in case of ship disaster • Offline coupling with a biogeochemical model (for research use) • Future issues: • How to initialize the high-resolution model • Tide assimilation method • Computational cost for the 4DVAR scheme 18

  20. Extra Slides 19

  21. Computational cost for the prototype 4DVAR system • OGCM: MRI.COM-WNP (~10km) • Number of grid: 673 x 442 x 54 • Time step: 10 min. • Assimilation window: 10 days • Observation: • Satellite altimeter • Gridded SST • In situ T-S profiles • Elapsed time by Earth Simulator2 (SX-9):  5hours (30 iterations, 64MPI) • Elapsed time by MRI super computer (SR-16000): •  4.5hours (10 iterations, 112MPI) 20

  22. Products and Users • JMA web: (figure and commentary) • To general users • (nowcast/forecast fields: SST, T, S, U, V, SSH, figure commentary) • JMA leased line: (Gridded point value: GPV; Grib/Grib2 format) • To Japan Coast Guard (JCG) : (nowcast/forecast fields: U,V) • To Japan Ministry of Defense (JMSDF) : (nowcast U,V,T,SSH) • To Japan Meteorological Business Support Center (JMBSC) • (nowcast/forecast fields: SST) • JMA radio facsimile broadcast (JMH): (figure) • To Japan Meteorological Business Support Center (JMBSC) • (nowcast/forecast SST) • To ships in the seas: (nowcast: U, V, T) • NEAR-GOOS data server: (figure, GPV) • To registered users (nowcast fields, of text file with the NEAR-GOOS format) 21

  23. Purposes of Ocean Information Service in JMA • Fisheries • Temp. front and Current at 0 - 500 m depth • Safe and economical shipping • SST, Strong Current and Sea Ice • Recreation • Temperature and current (near coast) • Rescue activity in case of ship disaster • SST and Current (high resolution) at surface • Prediction of oil drift • SST and Current (high resolution) • Coastal flood • Current variation and warm eddy approaching 22

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