Configuration Files - Initialization
To start, the current configuration files, master data sets, and the data forcing files are needed. The master data sets are downloaded from the Data page and include present day Antarctica and Greenland. However, these are at 5km resolution, and included in the zip files are the interpolated versions of the files, 20km for Antarctica and 15km resolution for Greenland.
for Antarctica, Antarctica_20km.zip
and for Greenland, Greenland_15km.zip.
These should all be put into the same directory with the configuration file.
Starting the Initialization
To get the spin-up running, type in the following to let Glimmer/CISM know to run the spin-up climate drivers.
to run the Antarctica model.
And to run the Greenland model,
Configuration File Headers
Configuration files are broken down into headers that are read by Glimmer/CISM to turn on certain functionality inside of the ice sheet model driver, glide. There are more than one type of glide climate drivers, and the ones used for Antarctica and Greenland are the spin glide drivers. Specific to the spin glide drivers are the [SPIN MB], [SPIN TEMPERATURE] and the [SPIN SLC] file headers. These three control the mass balance calculations (precipitation and the call to the annual positive degree day,pdd, module in Glimmer), the temperature calculations (the mean annual temperature and the half range temperature that is used in the pdd calculations), and the eustatic sea level.
In the configuration file the headers look like this:
[SPIN MB] model_type = 0 use_simple = 0
[SPIN Temperature] temp_file = vostok_125kyr_glimmer_friendly.data model_type = 0 use_simple = 0
[SPIN SLC] slc_file = ./specmap_125kyr_glimmer_friendly.data
The temperature and sea level forcing can be changed as desired to use the text files included in the zip files(or any text files that are properly formatted).
The Greenland model intialization also uses an isotope record to perturb the precipitation:
[SPIN MB] model_type = 1 use_simple = 0 oxygen_isotope_file = GRIP120kyr_oisotopes_glimmer_friendly.data
The forcing files are text files with model times and values. The first few lines of the sea level forcing file:
0.0 0.0 1000 -2.47293 2000 3.58749 3000 5.88627 4000 4.94586 5000 1.60218
arranged from start time of 0 to the end time, in this case 5,000 years of simulation time. The file must be in increasing order for Glimmer to correctly read the data in the file, and interpolate on each time step.
Changing the length of the simulation
Another important configuration file header to note is the one to do with the running time.
[time] tend = 125000 dt = 1.0 ntem = 0.5 nvel = 0.1
Tend is the total amount of time to run the model, 125,000 year, running with yearly time steps, dt = 1.0. The ntem and nvel options are factors on which to do temperature and velocity calculations for the model, in this case, nvel = 0.1, and the model is doing 10 calculations of the velocity per yearly time step.
The Final Product
Running the initialization creates a hotstart file, ant20_hot.nc, which can then be used to do some forward experimentation. It will look something like the file in the image below.
Future Forcing Configuration Files
The future forcing configuration files make use of the glint example climate code. The command and sequence is a bit different from initializing the model. Two configuration files are used, one is to run glint, and the usual ice sheet configuration file for glide. Also, global climate data is needed and is downscaled by calling glint and forced upon the ice sheet model. Lastly, the desired ice sheet hotstart file is needed, this is created in the above initialization run by selecting the hot variable in the output file. Provided are hotstart files for both Antarctica at 20km and Greenland at 15km grid resolution.
For the future forcing file, click here.
The hotstart file for Antarctica ant20km_hot.nc
The hotstart file for Greenland greenland15km_hot.nc
And the configuration files for Antarctica, Greenland and glint are in this zip file.
All of these should be included in the same directory.
An example of Greenland accumulation/ablation using the future forcing file, and present day Greenland surface.
Starting Glint Example
With all of the files in the same directory, glint can be started by typing:
which after hitting return will then prompt for the first configuration file:
Enter name of climate configuration file
Now enter in the glint configuration file name and hit return:
A second prompt will appear:
Enter name of GLIDE configuration file to be read
and then enter in the name of the ice sheet model configuration file to be run and hit enter, which in the case of Antarctica is:
and glint will now run, downscaling the climate to the ice sheet and calling glide yearly as it goes.
Glint Configuration File
For the future forcing runs, end time is set in the glint configuration file, along with some other important settings:
[GLEX climate] days_in_year=360 total_years= 95 climate_tstep=720 interpolate_climate=.false.
total_years is the length of the run. In this case the model is being forced by data sets gathered from 18 AR4 climate models. The data sets cover the period from 2004 through 2098. The data corresponds to the IPCC A1B scenario.
In the glint climate driver, the climate_tstep is defined in hours rather than years. The forcing data for temperature and precipitation are monthly means for the years of coverage. Instead of interpolating the data, as is the case in the original glint example, each frame of the input data file is read. And because glint is using an annual pdd scheme, the monthly data is accumulated for a year before mass balance is calculated by glide.