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Published byEunice Jacobs Modified over 9 years ago
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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
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Outline Objectives Tasks & progress Issues Next steps/ targets for next 6 months
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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
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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
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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
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Progress so far Successfully compiled and ran the SCM 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.
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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
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SCM test-case: with (top) & without physics (bottom) temperature humidity u-wind v-wind
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Relaxation of winds: u-wind with relaxation without relaxation
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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
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ERA interim data: temperature actual SCM without forcing SCM with forcing
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ERA interim data: humidity actual (log) SCM without forcing SCM with forcing
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ERA interim data: u-wind actual SCM without forcing SCM with forcing
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ERA interim data: v-wind actual SCM without forcing SCM with forcing
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Coupled model: full physics
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Coupled model: radiation, cloud & convection off
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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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