Geophysical Modelling: Climate Modelling How advection, diffusion, choice of grids, timesteps etc...
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Transcript of Geophysical Modelling: Climate Modelling How advection, diffusion, choice of grids, timesteps etc...
Geophysical Modelling:Climate Modelling
How advection, diffusion, choice of grids, timesteps etc are defined
in state of the art models
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
Model dynamics:
• Solves the “primitive equations” (Navier-Stokes Equations) on a rotating sphere.
• Prognostic equations for (u,v,w), θ, q, hydrometeors, etc.
• Mass continuity equation.• Variables are “initialised” (at t=0),
and are functions of (x,y,z,t), so prognostic equations are used to march forward in time and space.
Model physics:
• Many processes are “sub grid scale” and hence cannot be resolved
• These are parameterised…
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
Old Dynamics New DynamicsHydrostatic 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