CCSM BGC Working Group - Terrestrial Carbon Model
Intercomparison (Draft)
(Last revised: 2/27/06, Thornton)
Models:
Climate model: CCSM3, BGC branch
Terrestrial carbon codes: CASA’, CN, and IBIS
Standard resolution: T42 (2 x 2.5)
Runs:
1. Experiment 1: Forcing with observed NCEP/NCAR observations (CCSM3 Iconfiguration)
1.1. Experiment 1.1: Spin-up
1.1.1. CO2 constant at 283.1878 ppm. This is the value from the standard C4MIP
forcing file for year 1800 (the first year of that dataset).
1.1.2. N deposition climatology constant at pre-industrial level (circa 1890) for
CLM3-CN run. This climatology is provided by J.-F. Lamarque from
coupled CAM-Chemistry simulations. The T42 version of this file is located
at [to be done]. [Jean-Francois Lamarque is putting together the necessary
T42 N deposition files for time slices at 1850, 2000, and 2100. This new
dataset will include NOy+NHx deposition, whereas the previous T31 dataset
included only NOy.]
1.1.3. Surface data includes the plant functional type area fractions from
Johannes Feddema’s dataset for the year 1798, and the standard CLM input
datasets for special landcover types (glacier, lake, wetland). This dataset is
created at the T42 resolution, using the CLM utility for making surface
datasets, run script located at: [to be done]. [Peter Thornton is responsible
for creating this dataset].
1.1.3.1.Note: The surface dataset specification is relevant only to models
running with CLM as the base land component (e.g. CN and CASA’).
Other models using a different base land component (e.g. IBIS running
on LSX) will require appropriate model-specific surface datasets.
1.1.4. River routing module (RTM) turned on.
1.1.5. Memory allocated for all plant functional types on each gridcell
(MAXPATCH_PFT = numpft+1).
1.1.6. Climate drivers: Using the CCSM “data atmosphere” component datm7 to
cycle through 25 years (1948-1972) of NCEP/NCAR reanalysis data (from
A. Dai and T. Qian). The dataset is currently stored on the NCAR MSS at
mss:/TQIAN/LSMF/NCEPDATA as yyyy-mm.nc (1948-01.nc to 200412.nc).
1.1.7. Run with cyclic surface weather forcing until model reaches steady-state,
as defined below.
1.1.8. Spin-up acceleration: The models may employ model-specific
mechanisms to accelerate the approach to steady-state conditions. The only
criterion is that all models use the same external forcing data, as described
above, throughout the spin-up period.
1.1.8.1.Spin-up details for CN model: Uses the accelerated decomposition
(AD) mechanism introduced by Thornton and Rosenbloom (2005) to
reduce the number of model years required to reach steady state. First
step consists of a run initialized with very small leaf carbon and
nitrogen pools, and all other C and N pools set to zero. This step is run
for 500 years with the base rate constants for litter and soil organic
matter (SOM) decomposition multiplied by a factor of 10
(accomplished by setting AD_SPINUP flag as CPP variable in
clm.buildexe). Second step consists of a 25-year run (one cycle of
forcing) executed as a continuation from previous step, but with
AD_SPINUP turned off and EXIT_SPINUP turned on in clm.buildexe.
This switches the litter and SOM decomposition base rates back to their
normal values, and increases the litter and SOM pool sizes by a factor
of 10 on the first time step of the run. Third step consists of a run with
both AD_SPINUP and EXIT_SPINUP turned off and continuing to
cycle the 25 years of forcing data until the model reaches steady-state,
as defined below.
1.1.9. Criteria for definition of steady-state (must meet all of the following
criteria):
1.1.9.1.Global land NEE < 0.05 PgC/yr when taken as an average over the 25year repeat cycle (1948-1972) in the NCEP/NCAR surface weather
drivers.
1.1.9.2.For every model gridcell, absolute value of NEE < 1.0 gC/m2/y, taken
as an average over the same 25-year repeat cycle (guards against
spatially offsetting sources and sinks).
1.2. Experiment 1.2: Control
1.2.1. Start from the end-point of the Experiment 1.1 (spin-up), reset the
simulation year to 1798 and run forward with 25-year cycle (1948-1972) of
NCEP/NCAR forcing for 207 years, ending in simulation year 2004.
1.2.2. CO2, N deposition, and landcover held constant, as in spin-up (Expt 1.1).
1.2.3. The purpose of this experiment is to isolate any remaining drifts in the
model state variables, so that they can be removed from forcing experiments
by differencing.
1.3. Experiment 1.3: Varying climate
1.3.1. Branch from Experiment 1.2 at 1948-01-01 and run 57 years, through
2004, using the full NCEP/NCAR data record (1948-2004).
1.3.2. CO2, N deposition, and landcover are held constant, as in spin-up (Expt
1.1).
1.3.3. The purpose of this experiment is to isolate the influence of recent
historical climate changes on terrestrial carbon cycle.
1.4. Experiment 1.4: Varying climate, CO2, and N deposition
1.4.1. Weather drivers: Start from the end-point of the Experiment 1a (spin-up),
reset the simulation year to 1798 and run forward with 25-year cycle (19481972) of NCEP/NCAR forcing for 150 years (1798 – 1947), then switch off
NCEP/NCAR data cycling and run for another 57 years (1948-2004) using
the full NCEP/NCAR data record (1948-2004).
1.4.2. CO2 follows the C4MIP forcing file, which has values from 1800-1999.
For 1798 and 1799, the current dynamic CO2 mechanism in CLM will use
the value from 1800, moving into the transient at the start of the C4MIP
dataset (in 1800). [Extend the C4MIP dataset to 2004 (Mahowald)]
1.4.3. CN only: This run uses the N deposition time series from NCAR (see
1.1.2, above). The time slices at 1850, 2000, and 2100 are interpolated to
create an annual time series, which is ingested by the CLM3-CN code. Code
replicates data from the first time slice for any simulation years before the
start of the N deposition time series, in this case for the period 1798-1850.
1.4.4. Land cover held constant.
1.5. Experiment 1.5: Varying climate, CO2, N deposition, and land cover
1.5.1. Everything identical to Experiment 1.4, but adding the forcing of plant
functional type areas from the annual time series in Johannes Feddema’s
new datasets for the period 1798 – 2004. Treatment of land cover fluxes
follows the C4MIP protocol. [Provide additional details for landcover,
specific to Feddema’s datasets and the CLM plant functional type list
(Thornton).]
1.6. Experiment 1 Outputs
1.6.1. Save normal monthly history files for all experiments, including spin-up
1.6.2. Save special diagnostics for various periods of the transient experiments.
1.6.2.1.To do: define special diagnostics. What variables, what frequency?
2. Experiment 2: Coupled land-atmosphere, forcing from data sea surface
temperature and sea ice distribution, prescribed CO2
2.1. Experiment 2.1: Spin-up
2.1.1. Expt 2.1.1: Spin-up step 1 (F-configuration)
2.1.1.1.For each model: preliminary coupled CAM-land (F-configuration) run
to generate 25 years of hourly CAM forcings for use in spin-up. This
initial run is 50 years, with hourly output saved from the final 25 years.
These outputs are concatenated in a post-processing step to generate
CAM driver dataset for spin-up step 2.
2.1.1.2.Each land model is initialized from its own Experiment 1.1 endpoint.
2.1.1.3.Data SST and sea ice extent for this 50-year run are provided by
cycling twice through 25-years (1875-1899) of the HadISST dataset in
the docn component of CCSM.
2.1.1.4.CO2, N deposition, and surface datasets identical to those used in
Experiment 1.1.
2.1.2. Expt 2.1.2: Spin-up step 2 (I-configuration)
2.1.2.1.Each model uses 25 years of CAM drivers from its own Expt 2.1.1 as
cyclic forcing in data-atmosphere mode. Run until model reaches
steady-state.
2.1.2.2.Spin-up acceleration protocols and steady-state convergence criteria as
described above in sections 1.1.8 and 1.1.9, respectively.
2.1.2.3.CO2, N deposition, and surface datasets identical to those used in
Experiment 1.1.
2.1.3. Expt 2.1.3: Spin-up step 3 (F-configuration)
2.1.3.1.Switch back to active CAM-land (F-configuration), run 50 years to
assess the steady-state criteria.
2.1.3.2.Use the spun-up land state from the endpoint of Expt 2.1.2 as the
initial condition for land.
2.1.3.3.Use the endpoint for Expt 2.1.1 as the initial condition for atmosphere.
2.1.3.4.Data SST and sea ice extent for this 50-year run are provided by
cycling twice through 25-years (1875-1899) of the HadISST dataset in
the docn component of CCSM (same as in Expt 2.1.1).
2.1.3.5.CO2, N deposition, and surface datasets identical to those used in
Experiment 1.1.
2.1.3.6.Assess steady-state as defined in section 1.1.9 for final 25 years of this
50-year run.
2.1.3.7.If steady-state achieved, move on to Expt 2.2. Otherwise, run out Expt
2.1.3 until convergence criteria are met, or, if simulation is still very far
from steady-state, perform another segment in I-configuration with new
CAM forcing from final 25 years of Expt 2.1.3, then another segment
in F-configuration and test for steady-state again.
2.2. Experiment 2.2: Control (F-configuration)
2.2.1. Start from the end-point of the Experiment 2.1 (spin-up), reset the
simulation year to 1800 and run 205 years (1800-2004).
2.2.2. Data SST and sea ice extent from cycling 25 years (1875-1899) of
HadISST forcing.
2.2.3. CO2, N deposition, and landcover held constant, as in spin-up (Expt 1.1).
2.2.4. The purpose of this experiment is to isolate any remaining drifts in the
model state variables, so that they can be removed from forcing experiments
by differencing.
2.2.5. Transport land CO2 flux in CAM.
2.3. Experiment 2.3: Varying climate (F-configuration)
2.3.1. Start from the end-point of the Experiment 2.1 (spin-up), reset the
simulation year to 1800 and run 205 years (1800-2004).
2.3.2. Data SST and sea ice extent for the first 75 years (1800-1874) of this run
from three 25-year cycles (1875-1899) of HadISST. Starting in simulation
year 1875, switch docn cycling off and use HadISST years 1875-2004 for
the final 130 years of the simulation (1875-2004). [Check if the final months
of 2004 are available for HadISST dataset – currently we have only jan-feb
of 2004, so we might need to stop this run in 2003 (Thornton)].
2.3.3. Radiative CO2 follows the C4MIP historical transient for 1800-2004 (see
section 1.4.2), while biogeochemistry continues to see fixed CO2 at
283.1878 ppmv (the value circa 1800 from C4MIP forcing data).
2.3.4. N deposition landcover are held constant, as in Expt 1.1.
2.3.5. The purpose of this experiment is to isolate the influence of recent
historical climate changes on terrestrial carbon cycle, without the direct
biogeochemical effects of increasing CO2 and increasing N deposition.
2.3.6. Transport land CO2 flux in CAM.
2.4. Experiment 2.4: Varying climate, CO2, and N deposition
2.4.1. Start from the end-point of the Experiment 2.1 (spin-up), reset the
simulation year to 1800 and run 205 years (1800-2004).
2.4.2. Data SST and sea ice extent for the first 75 years (1800-1874) of this run
from three 25-year cycles (1875-1899) of HadISST. Starting in simulation
year 1875, switch docn cycling off and use HadISST years 1875-2004 for
the final 130 years of the simulation (1875-2004).
2.4.3. Radiative and biogeochemical CO2 follow the C4MIP historical transient
for 1800-2004 (see section 1.4.2).
2.4.4. This run uses the N deposition time series from NCAR for the period
1800-2004, as described in section 1.4.3.
2.4.5. Landcover held constant, as in Expt 1.1.
2.4.6. Turn on data ocean CO2 and data fossil fuel CO2 fluxes. The dataset for
ocean fluxes currently contains data for years 1850-2000. The dataset for
fossil fuel fluxes currently contains data for years 1900-1990. [Obtain
improved fossil fuel dataset (Mahowald), and examine the use of data from
Doney to extend OCMIP CO2 fluxes out to 2004 (Mahowald, Doney)]
2.5. Experiment 2.5: Varying climate, CO2, N deposition, and landcover
2.5.1. Everything identical to Experiment 2.4, but adding the forcing of plant
functional type areas from the annual time series in Johannes Feddema’s
new datasets for the period 1800 – 2004. Treatment of land cover fluxes
follows the C4MIP protocol.
2.6. Experiment 2 Outputs
2.6.1. Save normal monthly history files for all experiments, including spin-up
2.6.2. Save special diagnostics for various periods of the transient experiments.
2.6.2.1.To do: define special diagnostics. What variables, what frequency?
3. Experiment 3: Coupled land-atmosphere, forcing from data sea surface
temperature and sea ice distribution, prognostic CO2
3.1. ?
4. Diagnostics/Metrics
4.1. ?