[MITgcm-support] the implicit pressure components of PHIHYD?

[Martin Losch]

Hi CJ,

the composition of the diagnostics PHIHYD (totPhiHyd in the code) depends on the model configuration. For ECCO, I am guessing that the non-linear free surface with r-star coordinates is turned on and then totPhiHyd does not include the eta-contribution explicitly, but only impliclty via the variable r-star coordinate (this is more accurate, because then the free surface changes the layer thicknesses). Please have a look at model/src/diags_phi_hyd.F, starting line 107, which overwrites the default version at the top of the subroutine (which corresponds to your understanding of totPhiHyd). It’s probably going to be very tricky to reconstruct totPhiHyd exactly in this context (but I don’t know).

BTW, the conversion between pressure and geopotential is done with rhoConst (which happens to be 1029 in the ECCO context).

Martin

> On 19. Oct 2022, at 11:21, 秋菊陳 <ccj0315 at gmail.com> wrote:
> 
> Greetings,
> 
> I would like to get some clarification about the variable PHIHYD, both physical meaning and to relate the value with other variables (SSHDYN, RHOAnoma and EXFpress). 
> (e.g. https://data.nas.nasa.gov/ecco/data.php?dir=/eccodata/llc_90/ECCOv4/Release4/interp_daily <https://data.nas.nasa.gov/ecco/data.php?dir=/eccodata/llc_90/ECCOv4/Release4/interp_daily>. Yes, I am a ECCO data user.)
> 
> To my understanding, PHIHYD is the hydrostatic-pressure-anomaly/1029. The other way round, we could consider "PHIHYD*1029" as the sum of hydrostatic-pressure-anomaly ABOVE.
> From the schematic figure-1 below, the hydrostatic-pressure-anomaly of the first grid PHIHYD(1)*1029 could be treated as sum of 3 components:
> (1) atmospheric pressure (EXFpress), 
> (2) sea water pressure from sea surface (eta, SSHDYN) to z=0, i.e. g*( RHOAnoma+1029 )*SSHDYN 
> (3) sea water pressure from z=0 to first data grid z(1), i.e. g*RHOAnoma*abs(z(1))
> 
> However, I cannot get the result [sum of 3 components, fig2a green line] close to PHIHYD(1) [fig2a black line], unless ignoring component (2) [fig2a red line]. Did I misunderstand something?
> Any help would be appreciated.
> 
> Best,
> 
> CJ 
> 
> 
> 
> 
> 
> Figure-1                                                                                                                                  Figure-2
> <schematic.png>             <check_PHIHYD1_nasnasa.png>
> _______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.mitgcm.org/pipermail/mitgcm-support/attachments/20221019/5cad1f4c/attachment.html>