[MITgcm-support] Diagnostic for Heat flux from ocean to sea ice

[Martin Losch]

Hi Maddie,

the heat diagnostics are very confusing, and I don’t know if I can reconstruct them accurately (it’s been some time since I tried this):

oceQnet and SIqnet should be the same except fo the sign (oceQnet is positive downward and SIqnet is positive upward, so SIqnet = - oceQnet) *** in most cases *** (safe to assume also in your case). Both measure the heat the enter/leaves the ocean and it is hard to back out the sea ice part.

I think that SIqneti should be part of your diagnostic. From the code (seaice_growth.F), you can see that it records “r_QbyATM_cover”, which is the heat (Q) by the atmosphere (ATM) throught the ice (cover), entering the ocean, but you may need to add the heat flux from the ocean into the ice, diagnostic "’SIaQbOCN’” (available heat by ocean, usually melts ice, “a_QbyOCN").

SiamQnt is the heat entering the ice-ocean system, so that SIatmQnt-SIqnet should give you the net heat absorbed by the ice (from ocean and atmosphere).

Hope that helps. If not, you will have to find your way through seaice_growth.F, I am afraid.

Martin

> On 12. Aug 2024, at 13:18, Madison Shankle <mgs23 at st-andrews.ac.uk> wrote:
> 
> Hi all,
> 
> I'm looking for clarification on MITgcm's diagnostics regarding surface heat fluxes out of the ocean. I'm trying to measure whether heat flux from the ocean into sea ice is reduced between the two simulations I've run. 
> 
> The diagnostics I have at my disposal are as follows. If anyone is familiar with them, could you please advise which is the most appropriate to use in my case? I've also noted in each case a few points of confusion I have on each diagnostic.
> 
> oceQnet ("net surface heat flux into the ocean(+ =down), >0 increases theta") - This is (+) = down into the ocean, so this denotes the heat flux that the ocean receives, from both sea ice and from the atmosphere. I suppose negative values denote heat leaving the ocean (again either leaving to sea ice or to the atmosphere). Would multiplying this by fractional sea ice-covered area ("SIarea") give me heat flux into ice, where values are negative?
> oceFreeze ("heating from freezing of sea-water (allowFreezing=T)") - Unfortunately I can't use this as I did not set allowFreezing=True upon building my model. Oops!
> I then noticed there are sea ice-dedicated diagnostics, but these don't give results I expected for reasons noted below.
> SIqnet "Ocean surface heatflux, turb+rad, >0 decreases theta" - This is described in section 8.6.2.9 of the documentation as one of the "FLUXES ACROSS ICE-OCEAN INTERFACE (ATMOS to OCEAN FOR ICE-FREE REGIONS", so I thought that it might give me the heat fluxes going directly into the sea ice. However, per the description, it comes out exactly equal to oceQnet*-1. Since this diagnostic gives the heat flux for ice-free regions as well as ice-covered regions, I'm not sure (like with oceQnet) how to distinguish what heat flux the sea ice versus the atmosphere is receiving. (I also have the SIqneti and SIqneto diagnostics (the ice-covered and open-ocean parts of SIqnet, but they don't sum to SIqnet (due to SIqneti being four orders of magnitude smaller than SIqneto) so I'm not sure I'm understanding them correctly.)
> 
> SIatmQnt "Net atmospheric heat flux, >0 decreases theta" - This is described in section 8.6.2.9 of the documentation as one of the "FLUXES ACROSS ATMOSPHERE-ICE INTERFACE (ATMOS to OCEAN FOR ICE-FREE REGIONS)". This is nearly equal to oceQnet but differs slightly where there is sea ice. Is it the heat flux from the ice to the atmosphere? (But sea ice doesn't have "theta".) If so, then not helpful to me.
> 
> Thanks very much,
> Maddie Shankle
> 
> 
> 
> <Outlook-y5kigv2e.png>
> Maddie Shankle
> PhD Student, Paleoceanography
> School of Earth & Environmental Sciences   
> Bute Building, Queen's Terrace
> St Andrews, Fife, KY16 9TS
> 
> mgs23 at st-andrews.ac.uk <mailto:mgs23 at st-andrews.ac.uk> 
> www.st-andrews.ac.uk <http://www.st-andrews.ac.uk/>
>  
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