LANL CESM Exercise2

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Back to http://oceans11.lanl.gov/twiki/bin/view/Cosim/IceSheetsInCESM

View the results

Now we will look at some output from your IG run. If you haven't done this already, please do the following:

  • Open XWin server on your terminal.
  • Use Putty to connect to mapache with X11 forwarding enabled.
  • Once you have logged in, set up the CESM environment by typing this:
> source /usr/projects/cesm/scripts/mapache/pgi/cesm_env_script
 

These steps will allow you to view model output using ncview.

If all has gone well, your 5-year run should have completed successfully, and output should have been written to the designated short-term archive directory. Let's look at some archived files:

> cd ~/scratch2/username/CESM/archive/IGcase
> ls

You will see directories corresponding to different model components. The "rest" directory contains restart files that are needed to continue an earlier run without starting over from the beginning. Restart files are useful for long simulations that can take several days, weeks, or even months to complete.

Let's look in the land directory:

> cd lnd
> ls

There are two subdirectories called hist and logs. Let's look at some CLM history files:

> cd hist
> ls

You should see a netCDF file for each month of the run. Each file contains a number of monthly average fields. This command will tell you about the contents of the first monthly file:

> ncdump -h IGcase.clm2.h0.0001-01.nc | less

Use the space bar to scroll through the output.

Note the following:

  • The grid has 96 cells in the latitude direction and 144 cells in the longitude direction.
  • There are some time-independent variables (e.g., area, topo) with lower-case names.
  • There are many time-dependent variables with names in all caps.

We can visualize the data using the program ncview. To look at the output from January of year 5, type this:

> ncview IGcase.clm2.h0.0005-01.nc

If you did not finish a full 5-year run, you can replace 0005 above with the last full year of your run.

A blue window will appear on your screen. First, choose a field to view. Put your cursor over the box that says (176)2d vars and hold down the left mouse button. You will see a long list of fields. Position the cursor over the name of the field you want to look at and release the mouse button.

Let's look at the surface air temperature field. Move the cursor to the field labeled 'TSA'. You will see a map of global surface air temperature. Note the color bar on the control panel. To make the map larger, click on the box labeled 'MX3' using the left mouse button. To make the map smaller, click using the right mouse button.

Similarly, you can view output from July of year 5:

> ncview IGcase.clm2.h0.0005-07.nc

Notice the difference in the surface air temperature 'TSA'.

Next we will view the field 'QICE'. This is the surface mass balance of glaciated grid cells in units of mm/s. (To convert to the more useful units of m/yr, you would multiply by 3.16e4.) Values are positive where the ice is growing and negative where ice is melting.

Look at the annual average file for year 5:

> ncview IGcase.h1.0005-01-01-00000.nc

There are fewer variables in this file, so you can simply click on the box labeled 'QICEYR'. You should see a global plot of QICE on the global land grid. You can see QICE for glaciated cells not only in Greenland and Antarctica, but also in the Alaskan coastal range, Patagonia, the Himalayas, and the Canadian Archipelago. Note that the annual surface mass balance is positive for almost all of Antarctica. The mass balance is positive for most of Greenland, except for a patch in the southwest part of the ice sheet.

Recall that the surface mass balance is computed in CLM for multiple elevation classes and then downscaled to the ice sheet grid in CISM. Let's see what the mass balance looks like after downscaling. First go to the directory with GLC history files:

> cd /scratch2/username/CESM/archive/IGcase/glc/hist
> ls

View the file from year 5:

> ncview IGcase.cism.h.0005-01-01-00000.nc

You will see several 2D fields. First, view the ice thickness, thk. The thickness of the ice sheet does not change much during this short run.

Next, look at the surface mass balance, which in CISM is called acab (for accumulation/ablation). The units are m/yr. Initially you may see a blank field. Near the bottom of the panel, click on the current time box to advance to year 5.

Given constant atmospheric forcing from year to year, the model must run for several decades before the mass balance reaches a steady state. But the general pattern is apparent after a few simulation years. For unaltered NCEP forcing, the pattern is as follows:

  • In most of the ice sheet, the mass balance is small and positive (yellow shading).
  • In the southeast, the mass balance is large and positive (orange shading).
  • In the southwest and in some coastal regions, the mass balance is negative (red, green and blue shading).

These features are fairly realistic. The pattern would be improved if the surface mass balance were computed in CLM at higher (1 degree) resolution.

Depending on the size of the temperature change in your experiment, you may or may not see similar features in your CISM history file.

Next, put your CISM history file in a common directory where others can look at it. First, rename this file according to the temperature experiment you were running. If you increased the surface air temperature by 3 degrees, you would type this:

> cp IGcase.cism.h.0005-01-01-00000.nc cism.h.0005.tp3.nc

where tp3 means that you added 3 degrees to the temperature.

Similarly, you would type this if you lowered the temperature by 3 degrees:

> cp IGcase.cism.h.0005-01-01-00000.nc cism.h.0005.tm3.nc

where tm3 means that you subtracted 3 degrees from the temperature.

After renaming your file, please copy it to a common directory. If your file were called cism.h.0005.tp3.nc, you would type

> cp cism.h.0005.tp3.nc /usr/projects/cesm/cism/cism_hist_cesm/

Now change to that directory:

> cd /usr/projects/cesm/cism/cism_hist_cesm
> ls

If time permits, you can compare your file to other files in this directory. The control file, with zero temperature change, is called cism.h.0005.control.nc.