Dear Ryo,
Thanks a lot for an elaborate reply to my earlier query on "how to calculate vertical velocity from SODA3.15, 0.5degx0.5 deg monthly average?" downloaded from the source indicated earlier.
If I understand your response correctly, it is possible to get the vertical velocity using the continuity equation by smoothing 'w' appreciably. I would like to try it out because my earlier attempt without non-smoothing did not yield any reasonable structure for w.
However, I have a question because you say that because your numerical code uses B-grid and the Cartesian coordinates, u[x=@DDC] + v[y=@DDC] is the right calculation.
So, will the same calculation, w = u[x=@DDC] + v[y=@DDC], will work for the SODA data
set data
all.nclet div = (-1)*(u[x=@DDC] + v[y=@DDC])*4000 ! depth * div(u,v)
let div_s = div[i=@SHN:3,j=@SHN:3] ! a bit smoothed
let div_ss = div[i=@SHN:17,j=@SHN:17] ! heavily smoothed
plot/line/symbol/x=1030/L=1/hlimits=2400:3600 w, div, div_s, div_ss
frame/file=tmp.png
To get a robust result,
1. First, examine the SODA manual to find out what grid configuration SODA uses. For example, let's assume that it uses the C grid.
2. Use the C-grid continuity equation to calculate vertical velocity, which should be identical to the vertical velocity within SODA. (SODA must have vertical velocity internally. Whether it saves/outputs it or not is a separate issue.)
I don't think you can do this within Ferret.
Ryo