Table of Contents

LFM Grid Resolution

The LFM grid is available in several resolutions and operates most efficiently on the following processor counts:

• single: 53x24x32 cells on 8 processors
• double: 53x48x64 cells on 24 processors
• quad: 106x96x128 cells on 144 processors

Grid resolution and processor distribution must be specified at compile time. You can compile a particular model at a particular resolution via the following command:

gmake [input-code] RESOLUTION=[input-resolution]

where [input-code|input-code] is one of:

• LFM
• LFM-MIX
• LFM-RCM
• CMIT
• TIEGCM

and RESOLUTION=[input-resolution|input-resolution] is one of:

• RESOLUTION=single
  • 53x24x32 grid points
  • Distributed on 8 processors
• RESOLUTION=double
  • 53x48x64 grid points
  • Distributed on 24 processors
• RESOLUTION=quad
  • 106x96x128 grid points
  • Distributed on 144 processors
• custom (advanced users only): You can specify any custom resolution directly by specifying the number of grid points in each direction and number of processors. For example:

  NI=106 NJ=48 NK=64 NP=32

What is the physical domain of the grid?

Nearly all LFM grids extend to approximately (min, max) Earth Radii along the following axes:

• X-axis (sun-earth line): (-335, 30)
• Y-axis (in ecliptic plane): (-125, 125)
• Z-axis (normal to ecliptic plane): (-125, 125)

We have custom grids for special purposes.  These are:

• 64x48x64: Same as above, but the X boundary is exteded to (-335, 90) Earth Radii

What is the maximal number of processors I can use for my grid?

There are three constraints to determine the maximum number of processors that should be used for a particular grid:

• The LFM uses a 8th-order spatial method in each of the i, j and k directions. Therefore, each processor should have a ''minimum of 8 cells'' in each direction.
• The grid is decomposed spatially in terms of XY planes (i.e. in i-j space). The grid is currently not parallelized in the k direction.
• The grid decomposition only works for np > 1. Using a single processor (np=1) may give unexpected results.

A formula to determine the number of processors is:

Example 1: 53x24x32

For example, using the default on a 53x24x32 grid, and . So

So you can use up to 18 processors on a 53x24x32 grid.

Example 2: 106x48x64

On a 106x48x64 grid, and . So

So you can use up to 78 processors on a 106x48x64 grid.