Near real time forecasting of biogeochemistry in global GCMs Rosa Barciela, NCOF, Met Office

The Talk What are the aims? What tools are we using? What have we developed so far? Some preliminary results Assimilation of satellite-derived chlorophyll What will we be doing next? Are there any issues to be addressed? Conclusions

What are the aims? - NERC-CASIX: -estimates of air-sea fluxes of CO 2 -decadal re-analysis ( ) with/without ocean colour DA - Royal Navy -water clarity forecasts in the open ocean (5 to 7 days ahead) -improvement of light attenuation estimates: SST, MLD, sea-ice -minimise risks to maritime environment when deploying active sonar systems Different users have different needs: Pre-operational coupled physical-biogeochemical model by 2008

The Talk What are the aims? What tools are we using? What have we developed so far? Some preliminary results Assimilation of satellite-derived chlorophyll What will we be doing next? Are there any issues to be addressed? Conclusions

What tools are we using? –FOAM Forecasting Ocean Assimilation Model –HadOCC Hadley Centre Ocean Carbon Cycle Model Coupling together two models …

Forecasting the open ocean: the FOAM system Operational real-time deep- ocean forecasting system Daily analyses and forecasts out to 6 days Low resolution global to high resolution nested configurations Relocatable system deployable in a few weeks Hindcast capability (back to 1997) Assimilates T and S profiles, SST, SSH, sea-ice concentration FOAM = Forecasting Ocean Assimilation Model Real-time data Obs QC Analysis Forecast to T+144 NWP 6 hourly fluxes Automatic verification Product delivery Input boundary data Output boundary data

Hadley Centre Ocean Carbon Cycle Model (HadOCC) Model description: - Variable C:Chl ratio - Coupled to carbon & alkalinity - Normally used for climate studies - Transported around the ocean by physical processes - ‘NPZD’ ecosystem model

The Talk What are the aims? What tools are we using? What have we developed so far? Some preliminary results Assimilation of satellite-derived chlorophyll What will we be doing next? Are there any issues to be addressed? Conclusions

What have we developed so far? HadOCC embedded into FOAM at different resolutions (1º, 1/3º & 1/9º) 1/3º North Atlantic – Initial tests have been run with 1˚ global, 1/3˚ N Atlantic and Arctic and 1/9˚ N Atlantic FOAM configurations. – Nested system running successfully Data assimilation scheme for derived chlorophyll (ocean colour)

The Talk What are the aims? What tools are we using? What have we developed so far? Some preliminary results Assimilation of satellite-derived chlorophyll What will we be doing next? Are there any issues to be addressed? Conclusions

The impact of a phytoplankton bloom on air-sea CO 2 flux FOAM-HadOCC at 1º resolution, April 29 th – May 19 th 2000

Validation of FOAM-HadOCC results Validation of surface chlorophyll against SeaWiFS data Daily mean North Atlantic fields for 20 th April º Global 1/3º North Atlantic & Arctic 1/9º North Atlantic SeaWiFS 5-day composite

Validation of FOAM-HadOCC results Validation of subsurface structure vs AMT cruise data TemperatureSalinityChlorophyll 32.6W, 24.3N, 6 th June 2003 TemperatureSalinityChlorophyll 20.0W, 41.5N, 11 th June 2003 AMT obs 1/9º 1/3º 1º1º

The Talk What are the aims? What tools are we using? What have we developed so far? Some preliminary results Assimilation of satellite-derived chlorophyll What will we be doing next? Are there any issues to be addressed? Conclusions

Chlorophyll data assimilation scheme  Two stage analysis scheme:  Model chl vs. satellite obs: increments (ACS)  Balancing increments to biogeochemical variables  Phytoplankton increments derived using model biomass:chlorophyll ratio  Increments constrained to conserve total nitrogen & carbon at each grid point (if sufficient nitrogen is available)  Increments to other pools depend on the likely contributions to phytoplankton error from errors in growth and loss

Phytoplankton background error before the first analysis. Phytoplankton analysis error after the first analysis, with data everywhere. Phytoplankton errors (mmolN/m 3 ) Assimilation of derived chlorophyll Results from 3-D twin experiments

 “True” run - start from a spun-up model state, - model run for 1 year (Jan 2003 – Jan 2004) - forced by NWP 6 hourly surface fluxes - with physical (T, S, SST) data assimilation  Observations of Chl are taken from this “true” model state once a day.  Assimilation and control runs - HadOCC initialised using the fields from March physical fields taken from true run from April 2003  Assimilation run assimilates chl observations from the “true” run  Control run does not Ocean colour DA: tests in 3-D win experiments

Phytoplankton (mmol N/m 3 )Zooplankton (mmol N/m 3 ) Detritus (mmol N/m 3 )Nutrients (mmol N/m 3 ) Control - truthAssimilation - truth 3-D Twin experiments: daily mean RMS errors in the North Atlantic Total DIC (mmol C/m 3 )  air-sea exchange of CO 2 significantly improved after assimilating ocean colour data

Real world experiments  Global average RMS (solid lines) and mean (dashed lines) errors compared to the satellite chlorophyll data. Green: no DA Black: only physical DA Red: physical and biological DA

Real world experiments – on 1 st July 2003 Log(chl) from model with no biological assimilation Log(chl) observations Log(chl) from model with biological assimilation

The Talk What are the aims? What tools are we using? What have we developed so far? Some preliminary results Assimilation of satellite-derived chlorophyll What will we be doing next? Are there any issues to be addressed? Conclusions

What will be doing next? The key next steps are:  further quantitatively validation to initial FOAM-HadOCC integrations  parameter tuning (required to improve performance)  further refinement of ocean colour assimilation scheme  explicit biological feedback to physical model: downward radiation  run a 10-year re-analysis of FOAM-HadOCC with ocean colour and physical assimilation

The Talk What are the aims? What tools are we using? What have we developed so far? Some preliminary results Assimilation of satellite-derived chlorophyll What will we be doing next? Are there any issues to be addressed? Conclusions

Issues … Data assimilation:  Impact of physical assimilation on biogeochemistry: vertical mixing?  Quality of chl product: target accuracy in open ocean ~ 35% !!!  Chlorophyll versus IOPs/absorption? Validation:  Good temporal and spatial coverage for chlorophyll only (global – remotely sensed since 1997)  Other verifiable variables are: pCO 2 (North Atlantic?-VOS), nutrient (climatology, cruise data, time-series from monitoring stations)  Lack of verification for remaining fields: biomass (P,Z), detritus.

The Talk What are the aims? What tools are we using? What have we developed so far? Some preliminary results Assimilation of satellite-derived chlorophyll What will we be doing next? Are there any issues to be addressed? Conclusions

 an ocean colour data assimilation scheme has been designed and implemented within FOAM-HadOCC.  joint collaboration between University of Plymouth, NOC-Southampton and Met Office  real-world experiments show that the scheme is able to improve the chlorophyll: other biological fields are difficult to verify but some work is underway in this area Conclusions  the FOAM-HadOCC system has been run for 1 year at three resolutions  the system appears to be effective at simulating the onset of the spring bloom (good qualitative agreement with SeaWiFS and AMT data) but chl levels subsequently appear to be over-estimated.  higher resolution provides improved representation of advective processes in particular. However, benefits masked by large scale errors Model development Data assimilation

Rosa Barciela