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

Dynamical equations:

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

Model Grid

UM Horizontal grid

UM Vertical Grid

A climate simulation from climateprediction.net