Choosing a regional domain


Before you start

  • libs directory is dependent only on machine type. You do not need to touch it once successfully built.
  • rsm directory is dependent on the number of regional grids and the number of processors. If you want to change them, you need to rebuild rsm.
  • Regional doman is defined by the number of grid points (igrd and jgrd) and parameters.
  • Domain specification files are found in def/def_xxx/domainspec where xxx is one of gsm, rsm, crsm, gdas, scm, roms, nhm, in the sub directory whose naming can be easily identified.


RPROJ mapping projection index
  • 0 for Mercator projection (MP)
  • 1 for north polar stereographic projection (NPSP)
  • -1 for south polar stereographic projection (SPSP)
RTRUTH latitude where the map plane cuts through the earth’s surface
  • A north latitude for MP
  • 60o for NPSP
  • -60o for SPSP

RORIENT domain orientation longitude (this parameter is valid for PSP only??? usually same as RCENLON for MP)
RDELX grid spacing in meter in x-direction at RTRUTH.
RDELY grid spacing in meter in y-direction at RTRUTH.
RCENLAT reference latitude
  • domain center latitude for MP
  • 90o for NPSP
  • -90o for SPSP
RCENLON reference longitude
  • domain center longitude for MP
  • 0 for both NPSP and SPSP
RLFTGRD a grid number in x-direction
RBTMGRD a grid number in y-direction


Mercator projection

image001.gif
RLFTGRD = INT(Lx/RDELX): Grid number measured from (RCENLON, RCENLAT) to the west. Let us call this point L.
RBTMGRD = INT(Ly/RDELY): Grid number measured from (RCENLON, RCENLAT) to the south. Let us call this point B.
The total grid number in x-direction is igrd (measured from point L to the east).
The total grid number in y-direction is jgrd (measured from point B to the north).

Polar stereographic projection

image002.gif
RLFTGRD = INT(Lx/RDELX): Grid number measured from point B to the west. Let us call this point L.
RBTMGRD = INT(Ly/RDELY): Grid number measured from the pole to the south (in case of NPSP). Let us call this point B.
The total grid number in x-direction is igrd (measured from point L to the north).
The total grid number in y-direction is jgrd (measured from point B to the north).



First step (choosing igrd, jgrd, and parameters).

  • libs/etc/prmap is a very useful tool for choosing a regional domain. It reads igrd and jgrd from rsm/define.h and parameters from a model run script (such as rsm and rsim) in runs directory.
  • You do not need to compile rsm directory when choosing the domain. Just edit define.h and rsm, and run $ prmap rsm
  • prmap automatically launches GrADS and open prmap.ctl. Display any of four variables (fi, fj, flat, and flon) in prmap.ctl to visualize the domain.
  • Repeat the process of trial and error by changing numbers in define.h and rsm until you come up with the domain you desire.
  • igrd should be a product of integer powers of 2, 3, and 5. On IBM, integer power for 3 cannot be more than 2. This is a table for acceptable FFT length on IBM, but the table includes products of 7 and 11 too. Do not use those numbers with G-RSM. If you choose a wrong igrd on IBM machines the first error you see is probably from rmtn.x.
  • jgrd should be an odd number.

define.h

  • Next, go to rsm/def directory and copy a directory and name it rsm6228r$igrd$jgrd.
  • Edit igrd and jgrd in rsm6228$igrd$jgrd/define.h

configure-model

  • Go to rsm directory and edit the path to rsm6228r$igrd$jgrd in configure-model.
  • Type "make clean", "configure-model", and "make".
rsm_domains
  • Go to runs/rsm_domains and create a new *.h file for your new domain with the parameters of your choice.

configure-scr

  • Go to runs and edit configure-scr. Change the area name, resolution, and projection type, that matches the rsm_domains/*.h file you created.
  • Type "configure-scr rsm/rsim", and run the model...