ROMS Grid: what is essential?

[ckharris]

HI

What values are essential to getting a model grid that works?

We want to run ROMS in the York River, Virginia. We got a copy of a good HEM3D grid from J.I. Kwan, and want to convert it to a ROMS grid file. HEM3D, however, does not seem to need to know anything about grid cells that are land so we don't have lon/lat, pm, pn, etc. of land grid cells.

Do we need to have a reasonable set of grid cells to represent the land grid cells that border the York River and the smaller tidal tributaries off the York?

It would be a pain to fill in accurate lon/lat points for the land grid cells because the grid has a curve in it that matches the bend in the river here at Gloucester Point. Also, the grid has a lot of smallish channels.

Do you know whether ROMS will work if we fill in junk values for the land grid cells instead of reconstructing the grid over land and water?

Thanks
Courtney

[kate]

I expect all it really needs are non-zero values for pm, pn, and h. Try it and let us know.

[wilkin]

Add Coriolis to the essential list, but I'm pretty sure the lon/lat are not used internally. If the grid is curvilinear you will need the gradient metric factors dmdx and dnde. If you are going to apply boundary tides or use the point forcing option you may need the grid angle too.

[hetland]

Below is an ncdump -h of a minimalist grid, created with gridgen so land points are not defined, that works in roms.

I did linear interpolation on a retangular grid (i.e., using gridpoint values for x and y) of all the values, so that all of the values were defined everywhere, but just not used by the model. If I remember right, it complained when nans were used, even if they were on land. Also, doesn't ROMS use pn and pm one grid point into land to get metrics along the coast?

-Rob

netcdf ocean_grd {
dimensions:
xi_rho = 514 ;
xi_u = 513 ;
xi_v = 514 ;
xi_psi = 513 ;
eta_rho = 258 ;
eta_u = 258 ;
eta_v = 257 ;
eta_psi = 257 ;
variables:
double xl ;
xl:units = "meters" ;
double el ;
el:units = "meters" ;
char spherical ;
double pm(eta_rho, xi_rho) ;
pm:units = "meters-1" ;
double pn(eta_rho, xi_rho) ;
pn:units = "meters-1" ;
double mask_rho(eta_rho, xi_rho) ;
double mask_u(eta_u, xi_u) ;
double mask_v(eta_v, xi_v) ;
double mask_psi(eta_psi, xi_psi) ;
double dndx(eta_rho, xi_rho) ;
double dmde(eta_rho, xi_rho) ;
double angle(eta_rho, xi_rho) ;
double f(eta_rho, xi_rho) ;
f:units = "seconds-1" ;
double h(eta_rho, xi_rho) ;
h:units = "meters" ;

// global attributes:
:Description = "ROMS grid -- generated from gridgen" ;
:Author = "Robert Hetland" ;
:Created = "2006-09-30T16:53:39.200931" ;
:type = "ROMS GRD file" ;
}