Rules of Thumb

Rules of Thumb to run GEMCLIM

Match the FFT criteria
See that the number of points in x-direction matches the FFT criteria.
You can use 'findfft -h' to check.

Relation between time step and horizontal resolution
In general, the relation is linear. Here are some examples:
    Global 800x600: dt=900s
    LAM 0.5 deg: dt=1200s
    LAM 0.1375 deg: dt=450s
    LAM 0.0225 deg: dt=60s

Radiation time step: KNTRAD
Calculate new radiation tendencies about once per hour.
KNTRAD is set in time steps:
    KNTRAD = 3600 / Δ t

LAM: size of blending area
The blending/merging/sponge zone should be at least 10 points wide.
So far we had it cover about 2 points of the driving data. Meaning if the driving data are at 2 deg, have a sponge zone covering 4 deg. But there is a new theory now that 10 points might be enough for all resolutions. Still needs to be tested.

Tile size
LAM:     Keep the tiles as square as possible.
Global: Have as few tiles as possible in x-direction.
There must be 3 points in the free area of each tile. => LAM: If you have 10 points halo and 10 points blending your minimum tile size is 23 points.

LAM: Pil_dx
Set 'Pil_dx' to a resolution between the one of the driving data and the model resolution.
    Pil_dx = Resolution of driving data => fast entry, poor driving data interpolation quality
    Pil_dx = Resolution of model             => slow entry, good driving data interpolation quality

Author: Katja Winger
Last update: Apr 2011