[RegCNET] Question about preprocessing CFSv2 operational GRIB2 data for RegCM ICBC

[mohammad amini]

*Subject:* Question about preprocessing CFSv2 operational GRIB2 data for
RegCM ICBC

Dear RegCM developers and users,

I am currently working on setting up RegCM4.7.1 for seasonal forecasting
and I would like to use NCEP CFSv2 operational forecast data (in GRIB2
format) as the driving data for the model.

I understand that before running the ICBC preprocessor, the CFSv2 GRIB2
files must be converted to NetCDF format with a specific structure that
RegCM can recognize. However, I am facing some uncertainties about the
exact preprocessing steps and I would appreciate your guidance on the
following points:

1.      *Required variables:* Which specific variables from CFSv2
operational forecasts are needed for RegCM ICBC? I understand that the
required variables typically include:

o    3D variables: U, V, T, Q

o    2D variables: Surface pressure, Sea Surface Temperature (SST)

o    Are there any other mandatory fields (e.g., geopotential height, soil
variables)?

2.     *Which CFSv2 files to use:* CFSv2 operational data includes multiple
forecast hours and pressure levels. For RegCM ICBC:

o    Which forecast hours should be used?

o    Which pressure levels are required?

o    Should I use the pgbh (pressure level) files, the flux (surface flux)
files, or both?

o    Are ocnf files required for standard standalone RegCM runs?

o    For SST, should I use the sst field from the CFSv2 files or should I
use a separate SST dataset?

*3.    **About SST preprocessing:* Is it always necessary to run the SST
preprocessor separately alongside ICBC, or does it depend on the data
source and configuration? For instance, if the CFSv2 files already contain
SST fields, can ICBC directly use them, or do I need to extract SST and run
a separate SST preprocessor to generate SST files for RegCM? Under what
circumstances is running SST preprocessing mandatory?

4.     *NetCDF file structure:* What is the exact NetCDF structure expected
by RegCM's ICBC preprocessor?

o    What should be the variable naming conventions?

o    What are the required dimensions and attributes?

o    What should be the units and scaling?

o    Does the file need to follow any specific CF (Climate and Forecast)
conventions?

5.    *Preprocessing workflow:* Is there a recommended script or tool for
converting CFSv2 GRIB2 to the required NetCDF format? I have seen
references to prepare_cfs_for_regcm.sh (which uses wgrib2) and also the
possibility of using Python with xarray and cfgrib. Could you please
clarify the recommended approach?

6.     *Parameter settings in RegCM:* After preparing the NetCDF files,
what should be the values of dattyp and ssttyp in the RegCM namelist for
CFSv2 operational data? I have seen examples using dattyp = 'CFS01' and ssttyp
= 'CFS01', but I would like to confirm if this is correct for operational
forecasts (as opposed to reforecasts).

  7.*   Regarding the recommended RegCM version:* Is there a specific RegCM
version you recommend for use with CFSv2 operational data?



I have carefully read the RegCM User's Guide and searched the RegCNET
archives, but I could not find a detailed step-by-step guide specifically
for CFSv2 operational data. Any clarification, example scripts, or
references to documentation would be greatly appreciated.

Thank you in advance for your time and assistance.

Best regards,

Mohammad Amini
Senior Researcher

National Center for Climate and Drought Crisis Management (NCDCM)

Tehran, Iran
amini.mohammad at gmail.com
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