Customize CAM output

In this section, we will cover:

• how to change the output frequency

• how to control the number of time samples written to a history file

• how to output extra variables

• how to output extra history files

This can be achieved with 3 namelist variables:

• nhtfrq: sets the output frequency

• mfilt: maximum number of time samples written to a history file

• fincl: add variables to the history file

Customizing CAM output frequency: nhtfrq

The default history file from CAM is a monthly average. We can change the output frequency with the namelist variable nhtfrq

• If nhtfrq=0, the file will be a monthly average

• If nhtfrq>0, frequency is input as number of timesteps.

• If nhtfrq<0, frequency is input as number of hours.

For instance to change the history file from monthly average to daily average, we set the namelist variable:

    nhtfrq = -24     

Evaluate your understanding

The default history file in CAM is a monthly average. How do you modify the output to output 3-hourly data ?

Click here for the solution

Add the following line to user_nl_cam:

    nhtfrq = -3

Customizing CAM history files: mfilt

To control the number of time samples in the history file, we use the variable mfilt.
This variable specifies is the maximum number of time samples written to a history file.

For example, if we want to have 10 time samples on each history file, we can set the namelist variable as follows:

     mfilt = 10

To output daily data for a 1-year run in a single file, we can use the following values:

    nhtfrq = -24   
    mfilt = 365

If we want to output daily data with only 1 time sample per file, we can set the variables as follows:

    nhtfrq = -24
    mfilt = 1

NB: we cannot change mfilt for monthly frequency. For monthly frequency, we always have: mfilt = 1

Evaluate your understanding

What is the setting to generate 3 hourly data for a month-long simulation that will create a file every day?

Click here for the solution

Modify the length of the run in env_run.xml with the command:

    ./xmlchange STOP_N=nmonths, STOP_OPTION=1

Add the following line to user_nl_cam to output 3 hourly data and to create one file per day:

    nhtfrq = -3
    mfilt = 8

Add extra variables and history files: fincl

You can output up to 10 history files: h0, h1, …, h9.

• The h0 file contains the default variables or fields. (These are the variables you get by default without doing any modification to the namelist or code).

• For the files h1 to h9, the user must specify the variables to output.

To control the list of fields in the history files, use the namelist variable fincl

• fincl1 controls the fields in h0

• fincl2 controls the fields in h1

• …

• fincl10 controls the fields in h9

For example, to add the field PRECT to the h0 file, use the line:

    fincl1 = 'PRECT' 

Evaluate your understanding

What is the namelist setting to add:

• a hourly history h1 with the variables U, V, T

• and a daily history h2 with the variable PRECT

• and output 10 time samples in h1 and h2 ?

Click here for the solution

Add the following lines to user_nl_cam:

    nhtfrq = 0, -1, -24 
    mfilt = 1, 10, 10 
    fincl2 = 'U', 'V', 'T' 
    fincl3 = 'PRECT'

Averaging flag for the fincl variables

Using a : following a field gives the averaging flag for the output field.

Valid flags are:

• A ==> Average

• B ==> GMT 00:00:00 average

• I ==> Instantaneous

• M ==> Minimum

• X ==> Maximum

• L ==> Local-time

• S ==> Standard deviation

For instance, the line:

     fincl1 = 'PRECT:M' 

is used to add the minimum of PRECT to the file h0

Evaluate your understanding

What happens if we set in user_nl_cam:

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

Click here for the solution

In addition to the monthly history file h0,

• we will also output the file h1 with instantaneous values of T, Q, U, and V.

• These variables will be output every 3 hours, resulting in 8 time samples in each h1 file.

• A new file will be created every day.