[ecco-support] [EXTERNAL] Differences between forcing variables in flux-forced ECCOv4r4

[Wang, Ou (US 329B)]

Hi Dafydd,

We need all three variables: saltflx, sflux, and spflx and cannot use only one single flux variable impacting salinity.
The variable “saltflux” is the actual salt exchange between ocean and sea-ice. Salt will be trapped in sea ice when it forms and released to the ocean when sea ice melts. Salt related to this flux will be added to or removed from the surface ocean layer.
The variable “sflux” is virtual salt flux, i.e., the freshwater flux.
The variable “spflx” is the salt flux that is rejected into the ocean during freezing. Salt related to this salt flux gets redistributed vertically through the water column and acts to change the subsurface salinity, which is similar to the impact of the subsurface penetration of shortwave fluxes to temperature.

Similarly, we need both heat flux terms, total (hflux) and shortwave fluxes (swflux). You are right that the latter is needed for subsurface penetration of shortwave fluxes.

The statement in Fukumori et al. (2021) means the heat and freshwater fluxes are prescribed. Changing one will not change the other. While in the bulk-formula version, changing heat flux will change freshwater flux, or vice versa.

Best,
Ou


From: ecco-support <ecco-support-bounces at mit.edu> on behalf of Dafydd Stephenson <dafydd at ucar.edu>
Reply-To: "ECCO support list, wider membership" <ecco-support at mit.edu>
Date: Wednesday, April 6, 2022 at 3:55 PM
To: "ecco-support at mit.edu" <ecco-support at mit.edu>
Subject: [EXTERNAL] [ecco-support] Differences between forcing variables in flux-forced ECCOv4r4

Hi all,
I’ve recently set-up and run the flux-forced version of ECCOv4r4 (https://github.com/ECCO-GROUP/ECCO-v4-Configurations/tree/master/ECCOv4%20Release%204/flux-forced<https://urldefense.us/v3/__https:/github.com/ECCO-GROUP/ECCO-v4-Configurations/tree/master/ECCOv4*20Release*204/flux-forced__;JSU!!PvBDto6Hs4WbVuu7!bJGY--U5Hvlqcpw5zZklHFsDpRI3L7WV-nMnxtPPRbd3TlLj8BBXuwmGTiSb9gV33Zc$>), but some of the forcing variables used by this version do not seem to be documented in the MITgcm manual.

In particular, I am unable to find information on the variable “saltflx” other than a note added here http://wwwcvs.mitgcm.org/viewvc/MITgcm/MITgcm/doc/tag-index?revision=1.2291&view=markup&sortby=date&pathrev=checkpoint63<https://urldefense.us/v3/__http:/wwwcvs.mitgcm.org/viewvc/MITgcm/MITgcm/doc/tag-index?revision=1.2291&view=markup&sortby=date&pathrev=checkpoint63__;!!PvBDto6Hs4WbVuu7!bJGY--U5Hvlqcpw5zZklHFsDpRI3L7WV-nMnxtPPRbd3TlLj8BBXuwmGTiSbODdua34$> , and similarly “spflx” which I have believe is a “salt plume flux” in g/m2/s.

I have a few questions about this configuration:

  *   What is the difference (other than the units) between sflux and saltflx?
  *   Why are all three of saltflx, sflux, and spflx necessary for the flux-forced run, as opposed to a single flux variable impacting salinity?
  *   Similarly, why do we have two heat flux terms (hflux and swflux), the latter of which is entirely contained within the former (hflux = latent + sensible + lwflux + swflux) ? Is this related to the subsurface penetration of SW fluxes?
  *   The paper Fukumori et al., 2021, JPO (https://doi.org/10.1175/JPO-D-21-0069.1<https://urldefense.us/v3/__https:/doi.org/10.1175/JPO-D-21-0069.1__;!!PvBDto6Hs4WbVuu7!bJGY--U5Hvlqcpw5zZklHFsDpRI3L7WV-nMnxtPPRbd3TlLj8BBXuwmGTiSb2CXqclc$>), which uses this config, states: “whereas heat and freshwater fluxes are dependent in the bulk-formula version, the two are independent in the flux-forced version, thus permitting unambiguous determination of their individual effects.” – does independence here refer to the fact that they are not derived from common quantities (such as specific humidity), rather than being statistically independent, which would suggest they do not covary?

Thanks in advance for any help with this!
Best wishes,
Dafydd



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