# How the stream function and gradient function work

From: Guangshan Chen <gchen9_at_nyahnyahspammersnyahnyah>
Date: Mon, 24 Aug 2009 17:25:50 -0500

Dear all,

I did a test to the stream function (uv2sfvpf) and the gradient
function (gradsf). But there seems something is wrong in my script.

I used the uv2sfvpf function to calculate stream function from u and v
wind. Then I used the gradsf to calculate
u and v wind from the stream function that I calculated in the first
step. Last, I compared the original wind field
and the wind field calculate from the steam function.

These two wind field should be the same, supposedly. But the figure
show that they are quite different.

I attached my script and the figure. Could anyone give me a hand?
The following is the core of the code.

;;;;;;;;;;;;;;;;;;;;
; calculate stream function
;;;;;;;;;;;;;;;;;;;;
uvmsg = 1e+36
sf = new ( (/nlat,mlon /), float, uvmsg ) ; stream function
vp = new ( (/nlat,mlon /), float, uvmsg ) ; velocity potential

uv2sfvpf (uwind,vwind, sf,vp) ; u,v ==> stream function + velocity
pot
;;;;;;;;;;;;;;;;;;;;;
; calcualte the stream function's
; lat and longitudinal derivatives
;;;;;;;;;;;;;;;;;;;;;
sf_x = sf
sf_y = sf
gradsf(sf, sf_x, sf_y)

v_est = -sf_x
u_est = sf_y

copy_VarCoords(uwind,u_est)
copy_VarCoords(vwind,v_est)

Thanks in advance.

Guangshan

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Received on Mon Aug 24 2009 - 16:25:50 MDT

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