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What is fhocn and Fcondbot?

juliettelavoie

Juliette Lavoie
New Member
1. Is fhocn the same as Fbot defined in equ. (124) from the science guide?
Fbot=−ρ_w c_w c_h u∗ (Tw−Tf) (124)

2. I am working with the CESM-LE. Fcb (conductive heat flux at the bottom surface) variable is not available as an output. Can we calculate the Fcb with the difference between MELTH_F (Melt Heat Flux from Coupler from the ocean model) and fhocn? or the difference between MELTH_F and fhocn_ai?

Thank you for your help!
 

dbailey

CSEG and Liaisons
Staff member
These are good questions. Maybe the way to think about this is that the growth/melt at the base of the sea ice is:

dh / dt = Fc - Fbot

where the conductive flux (Fc) is upwards away from the bottom and the Fbot is oceanic heat flux. Now keep in mind, that Fbot is also bounded by the frzmelt term sent from the ocean. This is the so-called "heat available".

fbot = max(fbot, frzmlt) where frzmlt < fbot < 0.

The sign is such that a negative flux is heat lost from the ocean. Now, fhocn is the actual heat exchanged between the sea ice and ocean. So, MELTH_F should be the same as fhocn. The relationship between fhocn and fbot is as follows:

!-----------------------------------------------------------------
! Compute heat flux used by the ice (<=0).
! fhocn is the available ocean heat that is left after use by ice
!-----------------------------------------------------------------

fhocnn = fbot &
+ (esub + etop_mlt + ebot_mlt)/dt

So, it takes into account the energy of sublimation and melt as well. In terms of fhocn and fhocn_ai, this is just sea ice category weighted average fhocn or not. They are computed like this:

fhocn = sum(fhocnn(n)*aicen(n)) / sum(aicen(n)) where n is across the subgridscale categories.

fhocn_ai = fhocn * sum(aicen(n))

Dave
 

juliettelavoie

Juliette Lavoie
New Member
Thank you for your answer!

I am still not sure I totally understand...
First, you say that "MELTH_F should be the same as fhocn." They are not the same. Fhocn is massive when there is little ice. fhocn_ai is closer, but still there is still differences up to 6 Wm-2. (see figures of the difference between MELTH_f and [fhocn or fhocn_ai]. Different scales on the colorbar for each figure)
1.Any idea what the difference is?
2.Is MELTH_F the same as ebot_mlt/dt?
3.Is the comment "Compute heat flux used by the ice (<=0)." is refering to (esub + etop_mlt + ebot_mlt)/dt ?
4. Is melt and sub energy taken from the Fbot? OR Is Fbot a separate flux?
5.Why are the melt at the top and sublimation counting towards fhocn? Why is the ocean involve in surface processes?

Thank you for your help,
Juliette
 

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