Parameterisation & Resolution Flashcards
To resolve smaller weather phenomena, we need
More grid points
To improve initial conditions, we need
More data and better data assimilation
To improve the model, we need
Better resolution & better representation of physical processes
To embrace the chaos theory, we can use
Stochastic parameterisation and ensembles
Parameterisations show only the ___ aspects of the physical processes
Essential
Parameterised quantities can reflect
Clouds, precipitation, temperature, near-surface wind
If the phenomenon can be directly represented, we
Detect and present
If the phenomenon cannot be directly represented, we use
Diagnostic parameterisation
Four examples of parameterisations
Convection, orographic drag, cloud microphysics, surface-atmosphere fluxes
How to produce a parameterisation
Find relationships between small scale processes and grid-scale variables
Parameterisation is reductionist - what does this mean?
We assume we can explain the whole as a sum of its parts
The problem with using observations to test parameterisations
Processes parameterised are usually difficult to measure
2 examples of quantities needed to initialise parameterisations
Surface fluxes, aerosol concentrations
Special observations are used to produce paramaterisation relationships to
Relate them to model variables
Parameterisation relationships are assumed to be
Universal
Parameterisations act on a
Single profile
3 ways in which convection is parameterised
Dry convection, deep moist convection, shallow moist convection
Dry convection
Absolutely unstable
Deep moist convective
Conditionally unstable
Shallow, moist convection
Occurs in the boundary layer
3 factors that convection redistributes
Heat, moisture and momentum (wind speed)
Momentum is not redistributed in the parameterisation of
Deep,moist convection
3 things a convective parameterisation must decide
Activation, intensity and vertical distribution
Single biggest challenge in representing tropical rainfall
Convection parameterisation
How to explicitly represent unresolved processes
Increase resolution
Resolution of Met Office model
1.5 km
Global model resolution
10 km
Met Office transition resolution
4 km
Even at scales of 1-4 km, ___ is not truly resolved
Convection
Double the resolution leads to how much more computer power?
8x
Convective parameterisations are
Idealisations
