FAQ: Data ocean slab mode (DOCN-SOM)

[dbailey]

That is correct that Tmix is prognostic. The temperature (salinity, and velocities) are initial conditions. Only temperature is prognostic though and the rest remain fixed.

 

[zhaos]

Hello,

In pop_frc_mlt(mlann).ncl to derive SOM forcing files, a weight matrix M is applied to monthly climatological values. The effects seem to approximate:
VAL[current-month]=1.5*VAL[current-month]-0.5*VAL[previous-month]-0.5*VAL[next-month].

Is this a type of smoothing across time? what is the logic to determine this weight M?

Thanks very much for your help!

 

[dbailey]

This is a second order time differencing scheme.

 

[zhaos]

Thank you so much for your quick reply. Please excuse me for another question on this. invM seems to be:
1.43 -0.25 0.04 -0.01 0.00 -0.00 0.00 -0.00 0.00 -0.01 0.04 -0.25
-0.23 1.39 -0.23 0.04 -0.01 0.00 -0.00 0.00 -0.00 0.00 -0.01 0.04
0.04 -0.25 1.43 -0.25 0.04 -0.01 0.00 -0.00 0.00 -0.00 0.00 -0.01
-0.01 0.04 -0.24 1.41 -0.24 0.04 -0.01 0.00 -0.00 0.00 -0.00 0.00
0.00 -0.01 0.04 -0.25 1.42 -0.25 0.04 -0.01 0.00 -0.00 0.00 -0.00
-0.00 0.00 -0.01 0.04 -0.24 1.41 -0.24 0.04 -0.01 0.00 -0.00 0.00
0.00 -0.00 0.00 -0.01 0.04 -0.25 1.42 -0.24 0.04 -0.01 0.00 -0.00
-0.00 0.00 -0.00 0.00 -0.01 0.04 -0.24 1.42 -0.25 0.04 -0.01 0.00
0.00 -0.00 0.00 -0.00 0.00 -0.01 0.04 -0.24 1.41 -0.24 0.04 -0.01
-0.01 0.00 -0.00 0.00 -0.00 0.00 -0.01 0.04 -0.25 1.42 -0.25 0.04
0.04 -0.01 0.00 -0.00 0.00 -0.00 0.00 -0.01 0.04 -0.24 1.41 -0.24
-0.25 0.04 -0.01 0.00 -0.00 0.00 -0.00 0.00 -0.01 0.04 -0.25 1.42

This is different from the simple second order time differencing, e.g., Tt''=T(t+1)-2T(t)+T(t-1)?
Is there possibly a further explanation on this time differencing scheme?

 

[dbailey]

Oh, it actually takes into account the different length of months (30 versus 31).

 

[wkrantz]

Hello all, I'm designing a simulation using CESM2 in slab ocean mode in which I'd like to modify the q-flux forcing in a partlcular region dynamically based on local conditions. I've been taking a look at docn_comp_mod.f90 where the calculation for the SST are done using the q-flux defined in the forcing file that is set by DOCN_SOM_FILENAME.

My thought was that the best way to implement a regional dynamic forcing would be to define a custom mask that is checked in docn_comp_run, along with a few lines to calculate the q-flux per grid cell in the region defined by the mask.

However, I'm struggling to figure out the best way to define a new spatial mask that can be used by the calculations in docn_comp_run. I see that there is already an imask variable that is checked, presumably to define ocean gridcells where SST calculations should be done, but I can't find where that mask is defined or read from.

I initially thought that adding a new variable to the q-flux forcing file would be a good route, but I'm also having trouble finding where that forcing file is read in by the model and how to add a new variable that can be passed to the docn_comp_run subroutine.

Thanks for your help!

 

[dbailey]

There were experiments done (Pacemaker ensemble) where the SST in the tropical pacific was nudged to observations. Have a look at this work as it might provide some insight here. Basically, I would recommend doing the q-flux masking based on a lat / lon box. That is, I would add code to docn_comp_mod.F90 to have an "if" block that checks that lat and lon.

CESM2 Pacific Pacemaker Ensemble | Community Earth System Model

www.cesm.ucar.edu

 

[wkrantz]

There were experiments done (Pacemaker ensemble) where the SST in the tropical pacific was nudged to observations. Have a look at this work as it might provide some insight here.

Thanks for the reply, Dave! I'll look more closely into the setup for the pacemaker simulations.

Basically, I would recommend doing the q-flux masking based on a lat / lon box. That is, I would add code to docn_comp_mod.F90 to have an "if" block that checks that lat and lon.

If I want to define a simple lat/lon box in docn_comp_mod, I see that the existing calculation loops over a single index of n. Is there a simple mapping between n and lat/lon?

 

[dbailey]

You just need an if block that checks for lat between certain values and lon between certain values. Shouldn't matter what the index n is.

 

[wkrantz]

Hi Dave, thanks for your help so far. Like some others I have a question about achieving a stable equilibrium ocean temperature in a SOM setup. I am runing an 1850_CAM60_CLM50%SP_CICE_DOCN%SOM_MOSART_SGLC_SWAV compset with CESM2.1.3, and using the
pop_frc.b.e21.B1850.f09_g17.CMIP6-piControl.001_branch2.012120.nc forcing file from the inputdata directory.

After 30 years of simulation I'm still getting a steady warming (about 0.05 degrees C per year in global average SST). I'm wondering:
a) If I just need a longer spinup time to reach a steady state
b) If there is a mismatch between my configuration and the configuration that the forcing file is derived from
c) If it would be appropriate to apply a global offset to the forcing file to attempt to compensate for the energy imbalance

Any advice you have would be very helpful, thanks!

 

[dbailey]

It should equilibrate soon, but it might need a few more years. What is the TOA imbalance?

 

[wkrantz]

The radiative balance at top-of-model (FSNT - FLNT, weighted by gw) is 0.15 W/m2 on average, and I double checked that the area weighted average of qdp in the SOM forcing file is also very close to zero (-0.0029 W/m2), which I assume is all what I want. I'll keep running it and hope the SST levels out soon.

 

[Jerry]

Hi Dave, thanks for your help so far. Like some others I have a question about achieving a stable equilibrium ocean temperature in a SOM setup. I am runing an 1850_CAM60_CLM50%SP_CICE_DOCN%SOM_MOSART_SGLC_SWAV compset with CESM2.1.3, and using the
pop_frc.b.e21.B1850.f09_g17.CMIP6-piControl.001_branch2.012120.nc forcing file from the inputdata directory.

After 30 years of simulation I'm still getting a steady warming (about 0.05 degrees C per year in global average SST). I'm wondering:
a) If I just need a longer spinup time to reach a steady state
b) If there is a mismatch between my configuration and the configuration that the forcing file is derived from
c) If it would be appropriate to apply a global offset to the forcing file to attempt to compensate for the energy imbalance

Any advice you have would be very helpful, thanks!

Hi, Wkrantz,
I have run a case with the same compset "1850_CAM60_CLM50%SP_CICE_DOCN%SOM_MOSART_SGLC_SWAV".
But I don't find any ocn history output files. So I am wondering where you obtain the SST variable from.
I also want to check the trend of SST to assess whether my run has reached an equilibrium state.

​

 

[dbailey]

You can get the SST from the CICE component. Put the following in user_nl_cice:

histfreq = 'm','d','x','x','x'
histfreq = 1,1,1,1,1
f_sst = 'mdxxx'

This will give you monthly and daily SST.

 

[Jerry]

You can get the SST from the CICE component. Put the following in user_nl_cice:

histfreq = 'm','d','x','x','x'
histfreq = 1,1,1,1,1
f_sst = 'mdxxx'

This will give you monthly and daily SST.

Thanks! That does work!

 

[dbailey]

The answer is in a previous post, but basically you need to use the compset long name:

1850_CAM60_CLM50%SP_CICE_DOCN%SOM_MOSART_SGLC_SWAV

Then you need to make sure to set the DOCN_SOM_FILENAME in env_run.xml.