[ecco-support] [EXTERNAL] the potential density

[Fenty, Ian G (US 329C)]

Hi Ivana,

>> I want to calculate the potential density relative to the surface using ECCO output (THETA and SALT  fields....) and "density.m" function from gcmfaces, where "p" is the depth of tracer points, do I specify pref=0, and the potential density is given by rhop, as:  [rhop,rhpis,rhor] = density(t(:),s(:),p(:),pref(:));

That's what I would do.  You do have some choices about what to use for pressure.  You could directly convert model z depth to pressure in decibars or you could use the latitude-dependent pressure (e.g., the matlab seawater package 'sw_pres' from http://globec.whoi.edu/globec-dir/CTDSoftware/SeaWater/ ).

In case you are not aware, there is a Matlab representation of the JMD95 eos here:
https://github.com/MITgcm/MITgcm/blob/master/utils/matlab/densjmd95.m


>> If following Iudicone et al. (2008), I want to estimate the equation of evolution of the locally referenced potential density defined at a reference pressure chosen as the local pressure pr, I get that by multiplying the temperature tendency equation by alpha, salt tendency equation by beta, and combine them. In doing so, is this a correct way to obtain alpha?
>> alpha=sw_alpha(s(:),t(:),p(:),'ptmp'),
>>where again s is obtained from the SALT fields, t from THETA and p is the depth of the tracer points.

Yes, that is what I would do.  Again, you could choose a different eos to calculate alpha. The eos used in the seawater package 'sw_alpha' routine  seems to be same JMD: https://www.mathworks.com/matlabcentral/mlc-downloads/downloads/submissions/47595/versions/12/previews/mixing_library/private1/seawater/sw_aonb.m/index.html?access_key=

-Ian