# Re: [ferret_users] calculate the density with Pressure

Jean,
I use SODA1.4.2 data, when I type "show axis temp", only get the following information. No any useful.

"   name       axis              # pts   start                end   "

Dawn

jeanbrazil@xxxxxxxxxxx wrote:
Hi Dawn,
after run your scrpit, could you send me the data information from salt, temp, u or v (typing "show data") and axis of sal, temp , u or v and press (typing "show axis sal, temp , u , press ") ? I´m just dealing with similar work and  maybe I can help you a little more, ,if you want it of course.

Jean
----- Original Message -----
From: ferret ocean
Sent: Tuesday, January 23, 2007 3:24 PM
Subject: Re: [ferret_users] calculate the density with Pressure

HI Billy, Jim and Luck

"But the results are obviously wrong" means the density (got from let rho=rho_un(salt,temp,pres)-1000) is not corret, you will easilly find this problem when you plot figure. and when you execute " sta pres" and " sta k[g=u]", the two has different dimensions. I don't know how I can replace k[g=u] with pressure successfully in the function of rho_un.

Dawn

jeanbrazil@xxxxxxxxxxx wrote:
HI Billy, Jim and Dawn
I didn´t understand what you meant with "But the results are obviously
wrong", but check the units you are using (they should match with the
documentation) and replace "y[g=v]" by "y[gy=v]" and "z[g=v]" by

Luck

Jean

===========================================================

----- Original Message -----
From: "William S. Kessler"
To: "James Orr"
Cc: "William S. Kessler" ; "ferret ocean"
;
Sent: Tuesday, January 23, 2007 1:56 AM
Subject: Re: [ferret_users] calculate the density with Pressure

> Hi Jim, Dawn -
>
> No, I don't think Jim is correct. If a reference pressure is used, then
> you must use potential temperature theta instead of temperature. It does
> not make sense to calculate density at 0 pressure but with temperature at
> depth (where the pressure affects the temperature). Instead, bring the
> water parcel adiabatically to the surface by finding theta, then use your
> reference pressure:
>
> let theta=theta_fo(salt,temp,z[gz=temp],0) ! potential temperature
> theta
> let sigma_theta=rho_un(salt,theta,0)-1000
>
> See the documentation for the THETA_FO function. For sigma-2, use 2000
> instead of zero in the above.
>
> But I think Dawn is asking something different. Instead of z, she wants
> to use pressure. Frankly, I don't know the answer to her question ("the
> results are obviously wrong" doesn't give me much of a clue). However, I
> think she is on the right track, because I believe the 3rd argument to
> THETA_FO really should be pressure, not depth (the documentation is
> unclear on this point). I suggest looking at the reference given under
> the THETA_FO function (Bryden 1973). Then tell us so the documentation
> can be fixed if necessary.
>
> Billy K
>
> On Jan 22, 2007, at 9:59 AM, James Orr wrote:
>
>> Dawn,
>>
>> Your pressure in the 3rd argument of the rho_un function should be the
>> reference pressure:
>>
>> 0 for sigma_0
>> 2000 for sigma_2
>>
>> Cheers,
>>
>> Jim
>>
>>
>> On Mon, 22 Jan 2007, ferret ocean wrote:
>>
>>> Dear ferreters,
>>>
>>> I want to calculate the density with pressure instead of depth
>>> (more accuate way), but when I get the pressure with the following
>>> scipt to convert the depth to pressure,
>>>
>>> let x0 = sin(y[g=v]*3.1415926/180);
>>> let c1 = 5.92E-3 + x0*x0 * 5.25E-3;
>>> let pres = ((1-c1)-(((1-c1)*(1-c1))-(8.84E-6 * z[g=v]))^0.5) /
>>> 4.42E-6;
>>>
>>> then let rho=rho_un(salt,temp,pres)-1000;
>>>
>>> But the results are obviously wrong. Do you have any suggestions?
>>>
>>> Dawn
>>
>
>

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