Spin-up CTSM

The idea behind doing a so-called spin-up is to reach an equilibrium state in your model. Typically any perturbation (e.g. 2x CO2) experiment starts from such a state.

Running our perturbed system into equilibrium again will give you the maximum impact of the perturbation.

Which variables are important to check?

Since we are interested in the equilibrium state of our system, the “slowest” variables matter the most (e.g. terrestrial soil carbon).

BioGeoChemistry mode

If you are running in BioGeoChemistry (BGC) mode, it is important to check the health of your vegetation. The variable directly associated with the health is Total Leaf Area Index (TLAI).

If TLAI=0 your vegetation is dead and something went wrong.

How long should a spin-up be?

The overall duration (years before an equilibrium state is reached) varies. As mentioned above, the variables with the slowest turnover rate will define the time you’d need to spend for your spin-up.

The rule of thumb for single-cell simulation is the higher the latitude the longer the spin-up. Spinning up a single cell case in the Tropics will approximately take 2x100 years after which the terrestrial carbon pools are in equilibrium (Fig.1). In the polar regions, this means that the spin-up time is a couple of 1000 years!

Spin-up for a single cell case in the Tropics

What does equilibrium mean?

Typically you’d cycle through a range of given meteorological years - referred to as time-slice (e.g. 1990-2000).

After an initial rapid increase/decrease in your variables, you will start to see the interannual variability of the chosen time slice (wiggling). Equilibrium is reached as soon as consecutive time slices differ by less than a threshold that you have to choose (< 0.1-1%).

How to perform a spin-up?

Usually, we do a two-staged spin-up. See the necessary XML change commands below (NB you have to stand in the folder where you created your case for this to work!).

Accelerated decompositionNormal spin-up

Can be used for a reduced size of the carbon pools. The following code would be saved in the script ~/MY_CASE/tailor_my_case_acc_spin_up.sh, to tailor the type of case you want to run

  ./xmlchange CLM_FORCE_COLDSTART="on"
  ./xmlchange CLM_NML_USE_CASE="2000_control"
  ./xmlchange DATM_CLMNCEP_YR_START="1991"
  ./xmlchange DATM_CLMNCEP_YR_END="2010"
  ./xmlchange DATM_PRESAERO="clim_2000"
  ./xmlchange CCSM_CO2_PPMV="369."
  ./xmlchange STOP_OPTION="nyears"
  ./xmlchange RUN_REFDATE="0001-01-01"
  ./xmlchange RUN_STARTDATE="0001-01-01"

  #Additional xml changes for AD mode
  ./xmlchange CLM_ACCELERATED_SPINUP="on"

  #Number of years for spin-up 
  #For Tropics only STOP_N=100 is needed!
  ./xmlchange STOP_N=100

  #Frequency of restart files (1/4 of STOP_N)
  ./xmlchange REST_N=25

  #Setting wall clock time (on saga 5 years / 30 min)
  ./xmlchange JOB_WALLCLOCK_TIME=36:00:00
  ./case.setup
  ./preview_namelists