**To**:**"William S. Kessler" <William.S.Kessler@xxxxxxxx>****Subject**:**Re: [ferret_users] calculate the density with Pressure****From**:**James Orr <James.Orr@xxxxxx>**- Date: Tue, 23 Jan 2007 06:40:59 +0100 (CET)
- Cc: James Orr <James.Orr@xxxxxx>, ferret ocean <ferretocean@xxxxxxxxx>, oar.pmel.ferret_users@xxxxxxxx
- In-reply-to: <E8D79BD0-70CD-4ACB-A616-B63421070A3C@xxxxxxxx>
- References: <625997.17688.qm@xxxxxxxxxxxxxxxxxxxxxxxxxxx> <Pine.LNX.4.64.0701221856240.23830@xxxxxxxxxxxxxxxxxxxxx> <E8D79BD0-70CD-4ACB-A616-B63421070A3C@xxxxxxxx>
- Sender: owner-ferret_users@xxxxxxxxxxxxx

Jim On Mon, 22 Jan 2007, William S. Kessler wrote:

Hi Jim, Dawn -No, I don't think Jim is correct. If a reference pressure is used, then youmust use potential temperature theta instead of temperature. It does not makesense to calculate density at 0 pressure but with temperature at depth (wherethe pressure affects the temperature). Instead, bring the water parceladiabatically to the surface by finding theta, then use your referencepressure:let theta=theta_fo(salt,temp,z[gz=temp],0) ! potential temperature theta let sigma_theta=rho_un(salt,theta,0)-1000See the documentation for the THETA_FO function. For sigma-2, use 2000instead of zero in the above.But I think Dawn is asking something different. Instead of z, she wants touse pressure. Frankly, I don't know the answer to her question ("the resultsare obviously wrong" doesn't give me much of a clue). However, I think she ison the right track, because I believe the 3rd argument to THETA_FO reallyshould be pressure, not depth (the documentation is unclear on this point). Isuggest looking at the reference given under the THETA_FO function (Bryden1973). 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 thereference 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 (moreaccuate way), but when I get the pressure with the following scipt toconvert 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

-- James Orr Marine Environment Laboratories (MEL-IAEA) 4, Quai Antonie 1er MC-98000 Monaco Tel: +377 9797 7229 Fax: +377 9797 7273 Email: j.orr@xxxxxxxx

**Follow-Ups**:**Re: [ferret_users] calculate the density with Pressure***From:*mick spillane

**References**:**[ferret_users] calculate the density with Pressure***From:*ferret ocean

**Re: [ferret_users] calculate the density with Pressure***From:*James Orr

**Re: [ferret_users] calculate the density with Pressure***From:*William S. Kessler

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