General information

Domain & resolution

First you should decide upon the final(!) (see "Cascading" below) domain and resolution you want to run. For this it is important to know that:

the more grid points a grid has => the more cores are needed
the higher the resolution => the shorter the model timestep => the longer the runtime of the simulation

Have a look at the following wiki about how to set up a model grid: Set up a model grid

Number of points

Topology (MPI & OpenMP)

Resolution → timestep

The relation between the horizontal resolution and the model timestep is linear. Here are some examples:

Resolution [degree]	Resolution [km]	model timestep [sec]	For GY grid
0.009°	~1 km	30 s
0.0225°	~2.5 km	60 s
0.036°	~4 km	90 s
0.11°	~12 km	300 s
	~25 km	720 s	Grd_nj = 417
	~55 km	1800 s	Grd_nj = 171

Resolution → timestep → radiation timestep

Resolution → (non) hydrostatic

Model levels

LAM grid → top piloting or sponge

Global grid → adjust global pressure

Cascadeing

Spectral nudging

Period

Greenhouse gases / Scenario

Initial conditions

Driving data

Geophysical fields

Schemes

Land surface scheme (ISBA, CLASS, SVS)

Lake scheme (non, FLake, CSLM)

Urbain scheme (non, TEB)

Radiation

Roughness length

Limit ice /snow

Gravity wave drag

Emissivity

Condensation

Convection

Tracers to advect

Precipitation (Bourgouin)

Boundary layer

Horizontal diffusion

Output fields

Instantaneous / averages / min / max

Initial condition fields

Pilot fields (2-D / 3-D)

Output frequency

Output levels

Size of output files (monthly/daily/hourly/...)

Submission

Account

Wall clock time

On the clusters of the Alliance are different queues for jobs requesting different amounts of walltime as well as memory. To find out which type of queues exist on the cluster you want to run on check out the following wiki of the Alliance: Job_scheduling_policies

In the config file 'configexp.cfg' set 'BACKEND_time_mod' to the amount of seconds you want to request for a single job(1) - not for the whole simulation which can consist of multiple jobs.

In general, the shorter the requested time the shorter the queued time. Therefore, you want to request as little time as possible for a job. However, runtimes on clusters of the Alliance can vary by a lot, normally between -15 % to + 20 % of the average runtime. Hence, one should request runtimes that are about 25 % larger than the average expected runtime.

If you only want to run one job you can just request "enough" runtime. But when you are running a simulation with a sequence of jobs you might want to try to fit the jobs at the higher end of a queue. For Assuming, there are the following queues on a cluster:

3 hours or less,
12 hours or less,
24 hours (1 day) or less,
72 hours (3 days) or less,

And the simulation you want to run usually needs 14 hours per job.

Memory