PORT

Overview

PORT is a Parallel Offline Radiative Transfer software tool.

It is distributed as part of CESM. It diagnoses radiative forcing as described in a GMD paper, PORT, a CESM tool for diagnosing radiative forcing.

It is available as part of cesm1_2_beta07. The discussion below is in the context of this release.

It currently works with the CAMRT (cam4) radiation package. It also can work with the RRTMG radiation package, but MAM aerosols do not currently meet the interface requirements.

If you have a running version of CAM4 or CESM1, you can run PORT.

We look forward to hearing how this works or does not. There are no guarantees or waranties.

Configuration options

To specify that the CESM/CAM driver should invoke only the offline radiation driver, instead of all of CAM
- -offline_drv rad
To specify the radiation package
- -rad camrt (-rad rrtmg only works partially at this point)
A course-resolution PORT configure statement on a linux cluster might be:
- $cfgdir/configure \
- -offline_drv rad\
- -fc $USER_FC \
  -fc_type $FC_TYPE \
  -rad camrt\
  -chem none \
  -phys cam4 \
  -debug \
  -spmd \
  -nosmp \
  -dyn fv \
  -res 10x15 -cice_bsizex 3 -cice_bsizey 46 -cice_maxblocks 12 -cice_decomptype cartesian \

Namelist options

rad_driver_output = .true. samples the model state, heating rates, and fluxes necessary for offline diagnosis of forcing
offline_driver_fileslist = '/path/text_file_of_samples' is a file containing a list of files that are samples to be used in offline analysis
offline_driver_do_fdh = .true. Allow temperatures above the tropopause to equilibrate under the assumption of fixed dynamical heating
iradsw = 1, iradlw =1, iradae = 1 require all aspects of radiation to be computed every step
ndens = 1 produces double precision samples of the atmospheric state, so that the PORT analysis can be validated to roundoff (or bit-for-bit)
nhtfrq = 73 is found to be a good balance of sampling frequency, data size, accuracy, and precision
avgflag_pertape = "I" is necessary, since radiative transfer through (for example) average cloud fractions can be misleading.
rad_data_histfile_num = 2 (Default = 2) Place samples of state and radiative heating in the "h1" file.
rad_data_avgflag = 'I' Output samples of data rather than averages

Diagnostic outputs

FSNR is the shortwave (up) net flux at the tropopause
FLNR is the long wave (down) net flux at the tropopause
rad_qrs is the shortwave heating
rad_qrl is the longwave heating

Example of computing forcing due to doubling CO2

Sample the base state of a validated model for more than 16 months
1. Configure with -rad camrt -phys cam4
2. Add to the name list:
  1. iradsw = 1
  2. iradlw = 1
  3. iradae = 1
  4. ndens=1,1
  5. nhtfrq = 0,73
  6. mfilt = 1,1
  7. avgflag_pertape = 'A','I'
  8. rad_data_output = .true.
3. Run for more than 16 months
4. Create a file (/path/samples.inputs, as an example) that contains a list of the "h1" files (original.h1.file[n].nc) produced by this run.
Validate PORT (This step is not required, but is often useful for debugging errors in unusual configurations or untested architectures)
1. Configure CESM/CAM to compile the offline driver
  1. Configure with -offline_drv rad -rad camrt -phys cam4
2. Add to the name list:
  1. iradsw = 1
  2. iradlw = 1
  3. iradae = 1
  4. ndens=1,1
  5. nhtfrq = 0,73
  6. mfilt = 1,1
  7. avgflag_pertape = 'A','I'
  8. rad_data_output = .true.
  9. offline_driver_fileslist = '/path/samples.inputs'
  10. offline_driver_do_fdh = .true.
3. Validate
  1. There should be no difference between the fluxes, FLNT,FLNR,FLNS,FSNT,FSNR,FSNS from the sampling step (1) and the validation step (2).
Compute forcing due to a change in composition (CO2, as an example)
1. Modify the composition specified by the sample files:
  1. (In this example) for each file listed in /path/samples.inputs, ncap -s"rad_CO2=2*rad_CO2" original.h1.file[n].nc 2xCO2.file[n].nc
  2. create a new file (/path/2xCO2samples.inputs) that lists each of the modified files (2xCO2.file[n].nc)
2. Configure CESM/CAM to compile the offline driver
  1. Configure with -offline_drv rad -rad camrt -phys cam4
3. Add to the name list:
  1. iradsw = 1
  2. iradlw = 1
  3. iradae = 1
  4. ndens=1,1
  5. nhtfrq = 0,73
  6. mfilt = 1,1
  7. avgflag_pertape = 'A','I'
  8. rad_data_output = .true.
  9. offline_driver_fileslist = '/path/2xCO2samples.inputs'
  10. offline_driver_do_fdh = .true.
4. Forcing is the difference between
  1. the net flux at the tropopause (FLNR-FSNR) from the last 12 months of the sample files AND
  2. the net flux at the tropopause (FLNR-FSNR) from the last 12 months of the 2xCO2sample files

FAQ's:

Do I have to run with CAMRT (i.e., cam4 radiation)?
- RRTMG works, but FDH is not implemented and MAM aerosols do not work
Do I have to run with iradsw,iradlw,iradae = 1?
- No, but to validate that PORT is operating, it is necessary
Do I need to run with ndens = 1?
- No, but to validate that PORT is operating, it is necessary. And for RRTMG, validation is all but impossible without ndens=1
Can I use a different sampling, say nhtfrq =61?
- Of course, but other samplings may not divide the year evenly, nor sample solar zenith angle, or other problems
- We found that sampling every 73'rd time step was a good balance for dtime = 1800 and a 2-degree horizontal resolution for our purposes
- Other sampling schemes have been effective also
- For highly variable concentrations or correlations, every 73rd time step may not be a good choice
What does offline_driver_do_fdh = .false. do?
- It computes "instantaneous" radiative forcing by differencing FLNT-FSNT between runs
How do I give credit for the use of this code?
- Please reference our description paper, PORT, a CESM tool for diagnosing radiative forcing.

Child pages

Released version of PORT