Re: geostrophic current

[Billy Kessler <William.S.Kessler@xxxxxxxx>]

An obvious problem is that you cannot use file variables (y and z, 
in this case) as ordinary variables. The 2 statements below are
incorrect:

let f = 2*omega*sin(y*pi/180)
let rho = rho_un(ss[G=ggrid],tt[G=ggrid],z)

Try instead:

let yy=y[gy=ss]; let zz=z[gz=ss]

and then use yy and zz in the above two statements.

Billy K

> I have tried to calculate the geostrophic current with the
> script below by Dr. David Oxilia
> submitted to the mailing list on 15th Jan 1999.
> In addition, I have the World Ocean Atlas 1/4 (24 standard
> levels) supported by Dr. Jaison Kurian.
> However, I could not succeed in this calculation as some
> axis errors come. Especially I do not have confidence of
> two lines
> set reg/i=660:720/j=120:200/k=1:24
> and 
> let rho = rho_un(ss[G=ggrid],tt[G=ggrid],z)
> Could you give me some suggestions?
> 
> ============= geostrophic current script ==========
> ! Set your data file (I assume you have a netCDF file of
> model output)
> !!!use SaltTemp
> use woa01_salt.nc
> use woa01_temp.nc
> let ss=salt[d=woa01_salt.nc,l=1]  !!!WOA 1/4 salinity
> let tt=temp[d=woa01_temp.nc,l=1]  !!!WOA 1/4 temperature
> ! Set parameters
> let g = 9.81
> let pi = 3.14159
> let omega = 7.292e-5
> let f = 2*omega*sin(y*pi/180)
> define axis/x=160e:180e:0.25/unit=degree xxaxis
> define axis/y=60s:40s:0.25/unit=degree yyaxis
> define axis/z zaxis = {0, 10, 20, 30, 50, 75, 100, 125,
> 150,\
> 200, 250, 300, 400, 500, 600, 700, 800, 900, \
> 1000, 1100, 1200, 1300, 1400, 1500}
> define grid/x=xxaxis/y=yyaxis/z=zaxis ggrid
> ! Set region to all space (use actual values for ni, nj
> and nk)
> !set reg/i=1:ni/j=1:nj/k=1:nk
> set reg/i=660:720/j=120:200/k=1:24
> !!!set reg/x=165e:180e/y=60s:40s/z=0:1500
> 
> 
> ! Compute density
> ! I'll assume you have two variables S and T in your data
> file and that
> ! your vertical levels are in dbars (meters would be
> pretty close)
> let rho = rho_un(ss[G=ggrid],tt[G=ggrid],z)
> 
> ! Compute vertical shears
> let gamma = g/(rho*f)
> let u_z = gamma*rho[y=@DDC]
> let v_z = gamma*rho[x=@DDC]*(-1)
> 
> ! Compute geostrophic field
> ! To compute absolute velocity you either have to know
> some reference
> ! velocity or assume a level of no motion (as is
> traditionally done)
> ! The level of no motion argument is what is used when
> calculating
> ! the surface geostrophic field from "dynamic topography".
> You can
> ! assume that the flow is zero at the bottom for example
> and then
> ! integrate vertically to the level at which you want the
> flow field.
> 
> ! The flow field at the surface
> let u = u_z[k=@DIN]
> let v = v_z[k=@DIN]
> ! The flow field at the base of a 100 m mixed layer
> assuming the
> ! depth of no motion is at 5000 m.
> let um = u_z[z=5000:100@DIN]
> let vm = v_z[z=5000:100@DIN]
> 
> Takaya Namba
> 
> 
> 
> 
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