[MITgcm-support] Vertical heat balance in the ocean

[Martin Losch]

Hi Peter,

maybe a little naive, but doesn’t the net coolling flux at z=-30m (bottom of the first grid cell) reflect the cooling at the surface? For the system to stay in equlibrium, the surface heat flux must be balanced by a flux at the bottom of the cell, otherwise the temperature in the surface would change (dramatically). I guess what’s really relevant here is the heat flux divergence ( d fluxes / dz ), which then include the heat flux at the surface (and the penetrative sw-heat flux at each level).

The attenuation of sw-heat flux is hard coded in model/src/swfrac.F You can easily recompute that offline once you know Qsw at the surface.

Martin

> On 25. Aug 2020, at 15:48, Shatwell, Peter A <peter.shatwell12 at imperial.ac.uk> wrote:
> 
> Hello helpful MITgcm community,
> 
> I’m using the DDrake coupled configuration with a cube-sphere (C24) grid with 15 vertical levels (more details in Ferreira et al. 2010, https://doi.org/10.1175/2009JCLI3197.1), and I am trying to close the vertical heat balance in the model ocean.
> 
> I have computed vertical profiles of the advective vertical heat flux (diagnostic ADVr_TH) and the total diffusive vertical heat flux (diagnostics DFrE_TH and DFrI_TH). These advective and diffusive fluxes almost exactly balance throughout the water column (see attached figure), consistent with the traditional ‘upwelling-diffusion’ vertical balance of Munk ’66 and others (I’ve plotted it such that a positive flux is downwards i.e. a warming effect).
> 
> However, there is a strong departure from this balance in the top ~130 m of the ocean, indicating strong net upward cooling. Apparently penetrating shortwave radiation in the model could balance this cooling, but I am not sure how to properly confirm this. Are there existing model diagnostics to plot the shortwave penetration? Or could I estimate it from other outputs? 
> 
> Or is there something else that could provide a warming effect near the ocean surface? Or should I expect this balance to even hold at all?
> 
> Thanks and all the best,
> 
> Peter
> 
> --
> Peter Shatwell
> PhD student at MPECDT
> Space and Atmospheric Physics
> Imperial College London
> Huxley 714
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