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FAQ: Data ocean slab mode (DOCN-SOM)


CSEG and Liaisons
Staff member
I believe this is true, but I don't have as much experience here. The FC5 is a 1850 constant forcing, while the FAMIPC5 is time-varying forcing. Perhaps the former is more in line with your SOM experiment.


Haruki Hirasawa
New Member
Hello Dave,

I'm attempting to generate a SOM Q-flux file using CESM1-POP2 data from a Year 2000 simulation (last 100 years of a 500 year equilibrium simulation at this time). The climate in this simulation appears to be mostly equilibrated, so I thought it would be suitable for generating a SOM Q-flux. I started a timeslice run using Q-flux generated from this simulation using the pop_frc_mlt.ncl script. However, I found that about ~10 years into the simulation, the Y2000 Qflux case has a dramatic loss of summertime sea ice in the central Arctic (first attached figure for aice at ~81N,220E), rendering the Arctic ice free in summer. The sea ice cover is larger in the original Y2000 coupled simulation, so it seems like there is something wrong with the Qflux I've generated.

Do you have any advice on how to deal with this issue? Something I notice when comparing the September Y2000 to PI Qflux is that there is a small negative anomaly that extends into the Central Arctic (second attached figure). If I understand correctly, this means that there is an anomalous input of heat into the slab ocean layer. Could this be large enough to melt the ice entirely as I'm seeing?



  • pi_y2000_SOM_seaice.png
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  • pi_y2000_Qflux_septArc.png
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CSEG and Liaisons
Staff member
I would expect that a year 2000 SOM forcing file would be very warm from a climate state that is not in balance. That is why we tend to stick with 1850 picontrol runs as these are better equilibrated with a top of atmosphere of near zero. There is a Meehl et al. paper that talks about the issues of a 2000 control run.
Hi there,

I've recently been running cesm2.1.3 at resolution f19_g16 with the following compset: 1850_CAM40_CLM40%CN_CICE_DOCN%SOM_RTM_SGLC_SWAV

The slab-ocean forcing file is: pop_frc.b.c40.B1850CN.f19_g16.100105.nc

What I find is that the model becomes progressively colder and colder before crashing after approximately 35 years. This behaviour is surprising, and I'm wondering whether anyone else has seen this using cesm2 and a similar compset?




CSEG and Liaisons
Staff member
We have not run a many SOM simulations with the 2deg CAM. Also, you are running with CAM4 here. What is the top of the atmosphere imbalance here?


Etienne Dunn-Sigouin
New Member
Hi Dave,

I would like to create an instantaneous 2xCO2 run that branches from a piControl slab ocean simulation (compset E1850C5CN). I'm running cesm 1.1.2 and the piControl uses the SOM forcing derived from the fully coupled piControl available online.

After reading the user guide, I think all I need to do is change the variable 'co2vmr' from 284.7e-6 to 569.4e-6 since the 'scenario_ghg' variable is set to 'fixed'. Is this correct ? Are there other steps that need to be taken ?



CSEG and Liaisons
Staff member
Actually, there are two variables. That is one, but the other is in env_run.xml: CCSM_CO2_PPMV. This is for the land component.

This might be useful to users who need to know the exact definition of SHF. I figure out that the formula of SHF is

SHF = SHF_QSW + LWDN_F + LWUP_F + SENH_F + EVAP_F * latent_heat_vapor + MELTH_F - (SNOW_F + IOFF_F) * latent_heat_fusion * 1e-4

SHF > 0 means energy flux pointing downward (ocean receives energy)

This is validated in the output file of POP2 used in CESM1.2.2.1.
Quick verification code using ncap2 of nco
> ncap2 -v -s "check_residue=SHF-(SHF_QSW + LWDN_F + LWUP_F + SENH_F + EVAP_F * latent_heat_vapor + MELTH_F - (SNOW_F + IOFF_F) * latent_heat_fusion * 1e-4)" <input_file> <output_file>

My computed residue is about 0.001 W/m^2


Olivia Gozdz
New Member
Hi, grad student here-- I have a question about the surface heat fluxes in the SOM vs. FCM. The FCM has an outputted variable called SHF on the ocean grid (which seems to be calculated via equation tienyiah@uci_edu suggested above). I calculated the Fnet manually on the atmospheric grid for the FCM using equation Fnet = FSNS - FLNS - LHFLX - SHFLX, interpolated SHF to atmospheric grid and compared them.

SHF and Fnet both for the FCM surprised me, as they have pretty low correlations in the subtropics and tropics globally. I am wondering why SHF and Fnet for the FCM don't match-- what exactly is included in the model SHF calculation that is not physically included in the Fnet?

Thanks for any insights,


CSEG and Liaisons
Staff member
I assume by FCM you mean fully coupled model? The SOM forcing comes from a PI control (1850) control run. The SOM simulation as described in the FAQ at the top of this, just solved d(SST)/dt = (Fnet - Qflux) / (rho*cp*hmix). These are a climatological year which likely does not correspond to the period of your fully-coupled run.