Geophysical Modelling: Climate Modelling

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Geophysical ModellingClimate Modelling

• How advection, diffusion, choice of grids,
  timesteps etc are defined in state of the art
  models

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Example The UK Met Office Unified Model

• Same basic model is used for
• Global numerical weather prediction (i.e.
  operational weather forecasting)
• Regional NWP
• Climate modelling

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Model dynamics

• Solves the primitive equations (Navier-Stokes
  Equations) on a rotating sphere.
• Prognostic equations for (u,v,w), ?, q,
  hydrometeors, etc.
• Mass continuity equation.
• Variables are initialised (at t0), and are
  functions of (x,y,z,t), so prognostic equations
  are used to march forward in time and space.

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Model physics

• Many processes are sub grid scale and hence
  cannot be resolved
• These are parameterised

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Model physics

• Many processes are sub grid scale and hence
  cannot be resolved
• These are parameterised
• convection
• Cloud microphysics, precipitation etc
• Turbulence and heat exchange within boundary
  layer
• Radiative transfer (interactions with trace gases
  etc)
• Drag by mountains, gravity waves,etc
• Land surface processes

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Dynamical equations
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Old Dynamics New Dynamics
Hydrostatic Non-hydrostatic
Pressure based hybrid coordinate Height based hybrid coordinate Charney Phillips grid staggering
Arakawa-B grid Arakawa-C grid
Semi-implicit eulerian advection 2 time level semi-lagrangian advection
Richardson number based boundary layer scheme Equilibrium stable boundary layer scheme
Mass flux convection scheme with buoyancy closure Mass flux convection scheme with cape closure
Linear hydrostatic GWD scheme Warner and McIntyre type gravity wave drag scheme
Met Office Surface Exchange Scheme MOSES I Surface hydrology and soil model MOSES II
Standard Smith cloud scheme Standard Smith cloud scheme with prognostic cloud ice
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Model Grid
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UM Horizontal grid
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UM Vertical Grid
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A climate simulation from climateprediction.net
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