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.

 

[T_ying]

Hi Dave,
I'm running cesm1.2.2 with a compset of E1850C5, but the experiment design is for present day so I simply changed the level of GHGs as well as land use as 2000 levels. Does this sounds reasonable? From your previous discussion I've noticed that you suggest to run it at 1850 level rather than 2000 level, so I'm a little bit concern about it. Meanwhile, at the beginning of the simulation the toa energy imbalance is about 10 W/^2, which is due to GHGs, while after 40 years the simulation is still warming with a global mean toa energy imbalance of about 5~6 W/m^2. Should I keep running the simulation to reach its equilbrium or that's why there's no present-day compset such as E2000C5?
Best,
Tong

 

[dbailey]

Unfortunately we do not run long control runs for 2000 any more, so it is difficult to derive a "present-day" SOM forcing file. One can perhaps derive one from a JRA forced ice-ocean run (G-compset), but this is still not ideal. Keep in mind that the SOM forcing is not adding or taking away heat from the system (globally), so the SST will simply adjust to the atmospheric state. We have used 1850 SOM forcing for all of our 1x and 2x experiments.

 

[T_ying]

Unfortunately we do not run long control runs for 2000 any more, so it is difficult to derive a "present-day" SOM forcing file. One can perhaps derive one from a JRA forced ice-ocean run (G-compset), but this is still not ideal. Keep in mind that the SOM forcing is not adding or taking away heat from the system (globally), so the SST will simply adjust to the atmospheric state. We have used 1850 SOM forcing for all of our 1x and 2x experiments.

Hi Dave,
Thank you for your reply. My case seems to reach its equilibrium after 20 years that the global mean toa energy imbalance is below 0.5W/m2. I understand that the forcing file is based on preinsdustrial conditions. I've noticed the paper Gettleman et al 2019 discussing the climate sensitivity of CESM2, in which the some of the simulations are performed with SOM. I guess these are the experiments you mentioned that using 1850 forcing file, right? As for the unusual signals that I observed from my simulation, I think it is due to my emission settings while not problems with SOM. Thank you again~
Best,
Tong