salt_flux diagnostic identically zero in CM4

[StephenGriffies]

The diagnostic field "salt_flux" is identically zero in the CM4 simulations. This field should be nonzero, as it represents the transfer of salt between the liquid ocean and solid sea ice. There is either a problem with the diagnostic or a problem with the prognostic model. This issue should be high priority to debug, as the bug could cause major problems in sea ice regions if there is no salt exchanged between liquid and solid.

[MJHarrison-GFDL]

sea ice salt concentrations are 5 psu correct ? This is what is used in OM4_025 examples, but may not be in development runs.

[Hallberg-NOAA]

The salt flux would be 0 if we are
  still doing runs with the sea-ice salinity set to 0.

    - Bob Hallberg

  On 04/01/2015 04:28 PM, Stephen Griffies wrote:


  The diagnostic field "salt_flux" is identically zero in the CM4
    simulations. This field should be nonzero, as it represents the
    transfer of salt between the liquid ocean and solid sea ice.
    There is either a problem with the diagnostic or a problem with
    the prognostic model. This issue should be high priority to
    debug, as the bug could cause major problems in sea ice regions
    if there is no salt exchanged between liquid and solid. 
  —
    Reply to this email directly or view
      it on GitHub.

[StephenGriffies]

Did we indeed set the sea ice salinity to zero? If so, was that done for stability reasons? I do not recall the discussion in these regards...

[adcroft]

In CM4 ice_bulk_salin = 0.0. However, as far as I can tell in OM4 it is 0.05 which might explain some weirdness we've had. The intent had been to set the sea-ice salinity to 0 to avoid negative salinity arising from sea-ice formation over fresh water. SIS2 fixes this and works fine with a non-zero bulk salinity.

http://gitlab.gfdl.noaa.gov/mdt/xml/blob/9d0d088ae386c1829a2e58323862a9d41f6b33d7/CM4_proto.xml#L3331
http://gitlab.gfdl.noaa.gov/mdt/xml/blob/9d0d088ae386c1829a2e58323862a9d41f6b33d7/OM4.xml#L769

-A.

[StephenGriffies]

"...which might explain some weirdness we've had." "Weirdness" in CM4 or OM4?!!

[adcroft]

We had some Ob related extreme values a few months back when we were last
running OM4. I haven't had a chance to look into the cause...

-A.

Dr Alistair Adcroft ([email protected])
Princeton University Tel: (609) 987-5073
NOAA/GFDL, 201 Forrestal Road, Princeton, NJ 08540

On Thu, Apr 2, 2015 at 10:17 AM, Stephen Griffies [email protected]
wrote:

"...which might explain some weirdness we've had." "Weirdness" in CM4 or
OM4?!!

—
Reply to this email directly or view it on GitHub
#16 (comment)
.

[StephenGriffies]

By setting sea ice salinity to zero, do we adversely impact on the deep water formation mechanisms? That is, do we have zero brine rejection with zero sea ice salinity?

[adcroft]

Yes. We haven't looked at deep water formation OR had long enough runs to
worry about it yet. Again, I'm presuming SIS2 will be in use soon enough
that this is not an issue.

Dr Alistair Adcroft ([email protected])
Princeton University Tel: (609) 987-5073
NOAA/GFDL, 201 Forrestal Road, Princeton, NJ 08540

On Thu, Apr 2, 2015 at 10:38 AM, Stephen Griffies [email protected]
wrote:

By setting sea ice salinity to zero, do we adversely impact on the deep
water formation mechanisms? That is, do we have zero brine rejection with
zero sea ice salinity?

—
Reply to this email directly or view it on GitHub
#16 (comment)
.

[Hallberg-NOAA]

  When the sea ice salinity is zero, we
  get more brine rejection than when it is non-zero.  If ocean has a
  salinity of 35 ppt, setting the ice salinity to 0 gives a factor
  of 7/6 more brine rejection than setting the ice salinity to 5
  ppt.

    - Bob Hallberg


  On 04/02/2015 10:38 AM, Stephen Griffies wrote:


  By setting sea ice salinity to zero, do we adversely impact on
    the deep water formation mechanisms? That is, do we have zero
    brine rejection with zero sea ice salinity? 
  —
    Reply to this email directly or view
      it on GitHub.

[adcroft]

I've just checked that salt_flux is not zero in CM4 + SIS2 (for which we did not set the sea-ice salinity to zero). The pattern even looks sensible! 👍