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Coupled Model Data Assimilation:

Coupled Model Data Assimilation:. Building an idealised coupled system Polly Smith, Amos Lawless, Alison Fowler* School of Mathematical and Physical Sciences, University of Reading, UK * funded by NERC. Outline. Objectives Tasks & progress I ssues Next steps/ targets for next 6 months.

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Coupled Model Data Assimilation:

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  1. Coupled Model Data Assimilation: Building an idealised coupled system Polly Smith, Amos Lawless, Alison Fowler* School of Mathematical and Physical Sciences, University of Reading, UK * funded by NERC

  2. Outline • Objectives • Tasks & progress • Issues • Next steps/ targets for next 6 months

  3. Objective To use an idealised system to gain a greater theoretical understanding of the coupled atmosphere-ocean data assimilation problem: • explore different approaches to coupled 4D-Var data assimilation using a single-column, coupled atmosphere-ocean model • help guide the design/ implementation of coupled DA methods within full 3D operational scale systems • strong-constraint incremental 4D-Var

  4. Building the idealised system Task 1: develop an idealised, single-column, coupled atmosphere-ocean model with a strong-constraint incremental 4D-Var assimilation scheme. For this we need a model that • is simple and quick to run • is able to represent realistic atmosphere-ocean coupling Atmosphere: • ECMWF single column model (SCM) Ocean: • single column KPP (K-Profile Parameterisation) mixed-layer ocean model

  5. SCM: • based on the IFS code • includes a full set of physical parameterisations • we will use a stripped down version - adiabatic component (+ vertical diffusion?) • also want option to use full physics in later experiments KPP model: • developed at UoR • already within the SCM code but never been used • currently only works when full SCM physics scheme is switched on coupling through surface fluxes and SST

  6. Progress so far • Successfully compiled and ran theSCM test-case provided by ECMWF. • Simplified the SCM code to remove physical parameterisations. • Tested the simplified atmospheric model using real data. • Coupled the KPP ocean code to the full-physics SCM and successfully ran a test case for the coupled atmosphere-ocean model. • Produced draft documentation for the models.

  7. Issues • Lack of documentation • Choice of suitable test-case(s), creation of input file • Prescription of model forcing ocean: surface fluxes of heat, moisture & momentum, compute using bulk formulae of Large & Yeager atmosphere: vertical velocity, geostrophic u & v winds, horizontal advection tendencies. • Relaxation

  8. SCM test-case: with (top) & without physics (bottom) temperature humidity u-wind v-wind

  9. Relaxation of winds: u-wind with relaxation without relaxation

  10. Issues • Lack of documentation • Choice of suitable test-case(s), creation of input file • Prescription of model forcing ocean: surface fluxes of heat, moisture & momentum, compute using bulk formulae of Large & Yeager atmosphere: vertical velocity, geostrophic u & v winds, horizontal advection tendencies. • Relaxation

  11. ERA interim data: temperature actual SCM without forcing SCM with forcing

  12. ERA interim data: humidity actual (log) SCM without forcing SCM with forcing

  13. ERA interim data: u-wind actual SCM without forcing SCM with forcing

  14. ERA interim data: v-wind actual SCM without forcing SCM with forcing

  15. Coupled model: full physics

  16. Coupled model: full physics

  17. Coupled model: radiation, cloud & convection off

  18. Coupled model: radiation, cloud & convection off

  19. Next steps • Initial results with simple coupled atmosphere-ocean model expected by end of January 2013. • Development of prototype 4D-Var system - tangent linear and adjoint models preliminary results by April/May 2013. • Exploration of different coupling strategies being implemented in the ECMWF system - identical twin experiments

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