[MITgcm-support] Weird cooling with simple EXF setup

[Martin Losch]

Hi Yilang,

its the outgoing longwave radiation. It’s computed as emissivity*boltzmannConstant*[theta(in K)]^4, for 5degC surface ocean this will give 328W/m^2 upward heat flux.
This will cool your ocean until you reach a surface temperature of 0K if there is no balancing flux. Usually the incoming longwave and shortwave radiation do most of that. Have a look a any reanalysis data to get a feeling for the order of magnitude of the different heat fluxes.
In your case, since you turned of downward lw and sw radiation, the heat balance will be between outgoing longwave, and turbulent fluxes (sensible and latent heat), using simple exchange coefficients, you can estimate at which ocean surface temperature, these fluxes will be in balance. For a temperature difference of 5degC, the sensible heat flux is on the order of 100W/m^2, so much less than your longwave flux, which depends on the temperature to order 4. With your parameters, I would expect a surface temperature below 0degC to balance the heat flux at the surface.

Martin

> On 15. Nov 2019, at 09:30, Yilang Xu <yxu at whoi.edu> wrote:
> 
> Hi all, 
>  
> My last email did not get through the pipeline after 1hour, so sorry if a repeated message shows up later. 
>  
> I am testing EXF package, and am using the default EXF_OPTIONS.h file. In my data.exf, I have the following input, 
> Air temperature 10 degC all over the domain, with “exf_offset_atemp  = 273.15” added;
> Humidity 0.0001 all over the domain;
> Vwind ramps from 0 to 20m/s within certain area; 
> For uwindfile, precipfile, lwdownfile, swdownfile, runoffFile, I have input files with value 0 all over the domain. 
>  
> The ocean is initialized with 5 degC in data. During the runs, the ocean keeps cooling, with strong positive hflux and lwflux in STDOUT.0000. I checked exf_atemp in STDOUT, it is 283.15. So I am not sure why the ocean is getting colder even the air is warmer. 
>  
> My data.exf and STDOUT files are uploadedthrough Google drive. 
> https://drive.google.com/open?id=1H-Q-YZwYXdxay6jUXdfysjF1YHpL9mQ8
>  
> Appreciate it if anyone would help with this problem. 
>  
> Thanks,
> Yilang
>  
> File input within data.exf: 
>  hfluxfile         = ' ',
> sfluxfile         = ' ',
> ustressfile       = ' ',
> vstressfile       = ' ',
> atempfile         = 'airtempfield.bin',
> aqhfile           = 'humidfield.bin',
> uwindfile         = 'empty2dfield.bin',
> vwindfile         = 'vwind.bin',
> # evapfile          = 'empty2dfield.bin',
> precipfile        = 'empty2dfield.bin',
> lwfluxfile        = ' ',
> swfluxfile        = ' ',
> lwdownfile        = 'empty2dfield.bin',
> swdownfile        = 'empty2dfield.bin',
> runoffFile        = 'empty2dfield.bin',
> climsstfile       = ' ',
> climsssfile       = ' ',
>  
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