Modify CAM output#

Exercise: Customize your CAM history files

Create a case called b1850_high_freq using the compset B1850 at f19_g17 resolution.

In addition to the monthly history file h0, output:

  • h1 file with instantaneous values of T, Q, U and V every 24 hour.

  • h2 file with time-average values of T, Q, U and V every 3 hour.

Set your namelist so that you output:

  • a single h1 file with all the daily output for the month.

  • multiple h2 files, one for every day of the month.

Your goal is to produce:

  • one h1 file with 31 timesteps and

  • thirty-one h2 files with 8 timesteps each.

Set the run length to 1 month and make a 1-month run.

Click here for hints

# How do I compile?

You can compile with the command:

qcmd -- ./case.build

# How do I control the output?

Use namelist variables: nhtfrq, mfilt, fincl.

Look at the online documentation for these variables.

# How do I check my solution?

When your run is completed, go to the archive directory and navigate to the subdirectory atm/hist

cd /glade/scratch/$USER/archive/b1850_high_freq
cd atm/hist

(1) Check that your archive directory contains the files:

  • h0 files

b1850_high_freq.cam.h0.0001-01.nc

  • h1 files

b1850_high_freq.cam.h1.0001-01-01-00000.nc
b1850_high_freq.cam.h1.0001-02-01-00000.nc

  • h2 files

b1850_high_freq.cam.h2.0001-01-01-00000.nc
…
b1850_high_freq.cam.h2.0001-01-31-00000.nc
b1850_high_freq.cam.h2.0001-02-01-00000.nc

(2) Compare the contents of the h1 and h2 files using ncdump.

ncdump -h b1850_high_freq.cam.h1.0001-01-01-00000.nc
ncdump -h b1850_high_freq.cam.h2.0001-01-01-00000.nc

(3) Check the number of timesteps in the h1 and the h2 files. Look at the sizes of the files.

Click here for the solution

# Create a new case

Create a new case b1850_high_freq with the command:

cd /glade/work/$USER/code/my_cesm_code/cime/scripts/
./create_newcase --case ~/cases/b1850_high_freq  --compset B1850 --res f19_g17

# Setup

Invoke case.setup with the command:

cd ~/cases/b1850_high_freq 
./case.setup

# Customize namelists

Edit the file user_nl_cam and add the lines:

 nhtfrq = 0, -24, -3
 mfilt = 1, 31, 8 
 fincl2 = 'T:I','Q:I','U:I','V:I'
 fincl3 = 'T','Q','U','V'

# Set run length

Change the run length:

./xmlchange STOP_N=1,STOP_OPTION=nmonths

# Change the job queue and account number

If needed, change job queue and account number.
For instance, to run in the queue regular and the project number UESM0011 (You should use the project number given for this tutorial), use the command:

./xmlchange JOB_QUEUE=regular,PROJECT=UESM0011

# Build and submit

Build the model and submit your job:

qcmd -- ./case.build
./case.submit

# Look at your solution

When the run is completed, look into the archive directory for: b1850_high_freq.

(1) Check that your archive directory on cheyenne (The path will be different on otehr machines):

cd /glade/scratch/$USER/archive/b1850_high_freq/atm/hist
ls

(2) Compare the contents of the h1 and h2 files using ncdump. Look at the variables attributes. What is the difference between the 2 files ?

The file with the instantaneous output h1 have no cell_methods attribute while the average output h2 has a attribute:

cell_methods = "time: mean"

For instance for the field Q.

In the instantaneous file b1850_high_freq.cam.h1.0001-01-01-00000.nc

float Q(time, lev, lat, lon) ;
                Q:mdims = 1 ;
                Q:units = "kg/kg" ;
                Q:mixing_ratio = "wet" ;
                Q:long_name = "Specific humidity" ;

In the time-averaged file b1850_high_freq.cam.h2.0001-01-01-00000.nc

float Q(time, lev, lat, lon) ;
                Q:mdims = 1 ;
                Q:units = "kg/kg" ;
                Q:mixing_ratio = "wet" ;
                Q:long_name = "Specific humidity" ;
                Q:cell_methods = "time: mean" ;

(3) Check the number of timesteps in the h1 and the h2 files.

  • h1 contains 31 time samples.
    In the netcdf file,

time = UNLIMITED ; // (31 currently)

  • h2 contains 8 time samples In the netcdf file,

time = UNLIMITED ; // (8 currently)

  • Check the size of the files

du –ks –h /glade/scratch/$USER/archive/b1850_high_freq/atm/hist/*

234M    b1850_high_freq.cam.h0.0001-01.nc

210M    b1850_high_freq.cam.h1.0001-01-01-00000.nc
7.0M    b1850_high_freq.cam.h1.0001-02-01-00000.nc

55M     b1850_high_freq.cam.h2.0001-01-01-00000.nc
55M     b1850_high_freq.cam.h2.0001-01-02-00000.nc
...
55M     b1850_high_freq.cam.h2.0001-01-31-00000.nc
7.0M    b1850_high_freq.cam.h2.0001-02-01-00000.nc