Doubt regarding the vertical levels distribution in model

[tara]

Hello all,
ROMS is a sigma co-ordinate model. So, it follows the bathymetry to distribute all levels. Whether all levels are equally spaced or there is any way to control the distances between the levels or their distribution. let say i defined the 40 levels vertical resolution, how these 40 level will be distributed upto 200 depth. How the other parameters are involved in the distribution of vertical levels like- thetas,thetab,vtransform,vstretching,vtransform,tcline(hc)
.
assume-
N=40
Vtransform == 2 ! transformation equation
Vstretching == 4 ! stretching function

! Vertical S-coordinates parameters (see below for details), [1:Ngrids].

THETA_S == 07.0d0 ! surface stretching parameter
THETA_B == 0.1d0 ! bottom stretching parameter
TCLINE == 150.0d0 ! critical depth (m)




then how the all 40 levels will be distributed up to 200?

[kate]

There's a matlab tool to plot the s-surfaces in a vertical slice. You can also get some idea from this ROMS output:

Code: Select all

Vertical S-coordinate System, Grid 01:

 level   S-coord     Cs-curve   Z   at hmin       at hc    half way     at hmax 

    50   0.0000000   0.0000000        0.000       0.000       0.000       0.000
    49  -0.0200000  -0.0000415        0.208      -2.505      -4.757      -5.064
    48  -0.0400000  -0.0001667        0.417      -5.021      -9.760     -10.641
    47  -0.0600000  -0.0003782        0.625      -7.547     -15.016     -16.744
    46  -0.0800000  -0.0006800        0.833     -10.085     -20.538     -23.400
        :
     6  -0.8800000  -0.6677823        8.888    -193.473   -2167.514   -4294.395
     5  -0.9000000  -0.7273553        9.072    -203.419   -2347.321   -4663.427
     4  -0.9200000  -0.7869567        9.255    -213.370   -2527.211   -5032.632
     3  -0.9400000  -0.8453515        9.439    -223.169   -2703.554   -5394.460
     2  -0.9600000  -0.9012040        9.624    -232.651   -2872.420   -5740.744
     1  -0.9800000  -0.9531675        9.811    -241.646   -3029.851   -6063.253
     0  -1.0000000  -1.0000000       10.000    -250.000   -3172.195   -6354.390

My hmin is positive (above sea level) for the wetting and drying. My actual minimum dz is going to be small but positive. These particular numbers go with:

Code: Select all

          2  Vtransform        S-coordinate transformation equation.
          4  Vstretching       S-coordinate stretching function.
 7.0000E+00  theta_s           S-coordinate surface control parameter.
 2.0000E+00  theta_b           S-coordinate bottom  control parameter.
    250.000  Tcline            S-coordinate surface/bottom layer width (m) used
                                 in vertical coordinate stretching.

[tara]

Dear Kate,

Thank you very much for your reply,
In my case the distribution is

level S-coord Cs-curve Z at hmin at hc half way at hmax

40 0.0000000 0.0000000 0.000 0.000 0.000 0.000
39 -0.0250000 -0.0000295 -0.234 -1.877 -3.577 -3.756
38 -0.0500000 -0.0001188 -0.469 -3.759 -7.281 -7.772
37 -0.0750000 -0.0002707 -0.703 -5.645 -11.116 -12.060
36 -0.1000000 -0.0004899 -0.938 -7.537 -15.092 -16.639
35 -0.1250000 -0.0007831 -1.172 -9.434 -19.225 -21.539
34 -0.1500000 -0.0011592 -1.407 -11.337 -23.532 -26.798
33 -0.1750000 -0.0016299 -1.642 -13.247 -28.038 -32.468
32 -0.2000000 -0.0022095 -1.876 -15.166 -32.773 -38.610
31 -0.2250000 -0.0029158 -2.111 -17.094 -37.775 -45.301
30 -0.2500000 -0.0037705 -2.346 -19.033 -43.090 -52.636
29 -0.2750000 -0.0047998 -2.581 -20.985 -48.772 -60.728
28 -0.3000000 -0.0060353 -2.816 -22.953 -54.888 -69.714
27 -0.3250000 -0.0075147 -3.052 -24.939 -61.518 -79.758
26 -0.3500000 -0.0092834 -3.287 -26.946 -68.756 -91.057
25 -0.3750000 -0.0113956 -3.523 -28.980 -76.718 -103.845
24 -0.4000000 -0.0139158 -3.759 -31.044 -85.539 -118.402
23 -0.4250000 -0.0169212 -3.995 -33.144 -95.381 -135.064
22 -0.4500000 -0.0205034 -4.232 -35.288 -106.438 -154.227
21 -0.4750000 -0.0247720 -4.469 -37.483 -118.939 -176.366
20 -0.5000000 -0.0298569 -4.706 -39.739 -133.159 -202.045
19 -0.5250000 -0.0359130 -4.944 -42.068 -149.424 -231.936
18 -0.5500000 -0.0431244 -5.183 -44.484 -168.120 -266.836
17 -0.5750000 -0.0517098 -5.423 -47.003 -189.710 -307.695
16 -0.6000000 -0.0619292 -5.664 -49.645 -214.739 -355.640
15 -0.6250000 -0.0740908 -5.906 -52.432 -243.857 -412.007
14 -0.6500000 -0.0885607 -6.149 -55.392 -277.834 -478.384
13 -0.6750000 -0.1057723 -6.394 -58.558 -317.583 -556.650
12 -0.7000000 -0.1262391 -6.641 -61.968 -364.185 -649.033
11 -0.7250000 -0.1505679 -6.891 -65.668 -418.917 -758.163
10 -0.7500000 -0.1794756 -7.143 -69.711 -483.289 -887.149
9 -0.7750000 -0.2138069 -7.399 -74.161 -559.078 -1039.654
8 -0.8000000 -0.2545552 -7.659 -79.092 -648.377 -1219.987
7 -0.8250000 -0.3028863 -7.924 -84.591 -753.639 -1433.202
6 -0.8500000 -0.3601634 -8.194 -90.762 -877.734 -1685.212
5 -0.8750000 -0.4279753 -8.471 -97.723 -1024.007 -1982.906
4 -0.9000000 -0.5081650 -8.755 -105.612 -1196.338 -2334.275
3 -0.9250000 -0.6028587 -9.049 -114.589 -1399.202 -2748.541
2 -0.9500000 -0.7144926 -9.353 -124.837 -1637.730 -3236.268
1 -0.9750000 -0.8458353 -9.669 -136.563 -1917.748 -3809.461
0 -1.0000000 -1.0000000 -10.000 -150.000 -2245.811 -4481.622


that means according to you, where hmin=10
tcline=150
hhalfway=2246
hmax=4482
values of depth will be present then I will get this distribution and other than these depth values it(Hz) will depend on the H z ≡ ∂ z /∂ σ .So, in whole domain as per bathymetry the number of these 40 levels distribution is not uniform. It is variable this is why we can not say specially for coastal region what is my fixed resolution because it is varying at all different depth locations. So, hmin and tcline values are the most important values to set the expected distribution of vertical levels in coastal regions specifically.If I am not please correct me.


With Regards-
Tanuja

[sonaljit.m]

Hi all,
I'm new to modeling in ROMS. I am trying to setup the vertical grid for my simulations based on Shchepetkin 2005, using the function pyroms.vgrid.s_coordinate_4 (pyroms). Here's the code:
theta_b = 0.1
theta_s = 7
Tcline = 1000
N = 16
vgrd = pyroms.vgrid.s_coordinate_4(h, theta_b, theta_s, Tcline, N, hraw=hraw)
I'm plotting the s surfaces (h*vgrd.s_rho) over longitude and depth (plot attached).

As you can see, the s surfaces are uniformly spaced along the vertical. However, what I need is for the distance between the s surfaces to gradually increase with the depth (finer resolution near the surface and coarser near the bottom). I understand that theta_s and theta_b are for tweaking the resolutions at the surface and bottom respectively, and Tcline is for setting the depth within which the resolution will be finer(?) However, I am getting the exact same s_rho even after applying different values for these variables.

What am I missing here? Should the variables be entered in a different manner?

Thank you.

[wilkin]

There is a relatively detailed explanation on WikiROMS of how stretching alters with the different transform and parameter options:

https://www.myroms.org/wiki/Vertical_S-coordinate