FAQ: CICE4 to CICE5 initial files

[dbailey]

In order to use CICE4 initial files with the new CICE5 code base in CESM2 requires some processing in order to avoid problems. Note that CICE5 is the only code base available in CESM2, so if you want to use older CICE4 files to initialize a run they will need to be converted. We have an NCL tool that will convert older CICE4 style files into a format that CICE5 can read. This NCL script is attached here. The main inputs the user needs to modify are near the top of the script:

case = (name of the input case. e.g. b.e11.B20TRC5CNBDRD.f09_g16.001)

year = (year of the file. e.g. 1955)

phys = (flag selecting the physics used to create the input file. e.g. 'cice4' or 'cice5')

The *phys* flag is particularly crucial for this script. The input initial file is always assumed to be from a run using the CICE4 code base. For phys = "cice4" then it means the new run with the CICE5 code base will be using the old CICE4 physics options:

ktherm = 1
tr_pond_cesm = .true.
nilyr = 4 (number of sea ice vertical layers)
nslyr = 1 (number of snow vertical layers)

For phys = "cice5" then it means the new run will use the default physics options in CICE5, which are as follows:

ktherm = 2
tr_pond_lvl = .true.
nilyr = 8 (number of sea ice vertical layers)
nslyr = 3 (number of snow vertical layers)

Dave