[MITgcm-support] Evaporation in sea ice regions

Martin Losch Martin.Losch at awi.de
Tue Jul 23 08:56:40 EDT 2019

Hi Kaitlin,

I agree with you that this is a little confusing.

Until recently (and you’ll have to check the version of your code), the exf-diagnostics did not know about the presence of sea ice (neither did the exf-bulkformulae, so that you can have quite funny values over sea ice). I think this has changed recently (PR #203 was merged on Jun19, see <https://github.com/MITgcm/MITgcm/pull/203>).

Before that

'SIatmFW ‘ is the net freshwater flux from atmosphere and land (includes runoff and precip), including the entire sublimation. You could just subtract precip and runoff (which you normally prescribe) and use that as total evapo-sublimation. 

'SIhl    ‘ is the latent heat flux (including evap and sublimation) into the ocean, could also be converted to freshwater flux

SIfwSubl, SIacSubl, SIrsSub are potential, actual and residual fw flux by sublimation. 
SIfwSubl tells you how much latent heat there was available for sublimation (in units of fw).
SIacSubl is the actual sublimation flux that enters SIhl
SIrsSubl is what’s left of SIfwSub, after all of the snow and ice have been sublimated away. This is then used to evaporate from the now exposed ocean.

SIatmFW contails SIfwSubl (so sublimation of snow, ice, and if necessary ocean) and
SIatmFW-EXFprecip-EXFrunoff is the correct diagnostic (although I am not sure).

(I hope that this is correct)


> On 23. Jul 2019, at 11:51, Naughten, Kaitlin A. <kaight at bas.ac.uk> wrote:
> Hello,
> I am trying to calculate evaporation in my domain, which contains both sea ice and open ocean. I can't figure out what the EXFevap diagnostic represents in sea ice covered regions. Is it the evaporation which actually happens (i.e. considering the sea ice) or the evaporation which would have happened if there was no sea ice (based on the SST below the ice)?
> Furthermore, is sublimation included in the evaporation fields, or is this completely separate? I see some sublimation diagnostics (SIfwSubl, SIacSubl, SIrsSubl) but am not sure if adding them to evaporation would be double-counting.
> Many thanks,
> Kaitlin Naughten
> Dr Kaitlin Naughten
> Ocean-Ice Modeller
> British Antarctic Survey
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