era5_to_int

A simple Python script for converting ERA5 netCDF files to the WPS intermediate format

Overview

The era5_to_int.py script converts ERA5 model- or pressure-level netCDF files to the WRF Pre-processing System (WPS) intermediate file format, permitting the use of these data with either the Weather Research and Forecasting (WRF) model or the Model for Prediction Across Scales - Atmosphere (MPAS-A).

The only required command-line argument is the date-time, in YYYY-MM-DD_HH format, of ERA5 files to convert. For example:

era5_to_int.py 2024-05-01_00

Conversion of a range of date-times is possible through the use of additional command-line arguments as described in the Usage section.

The following surface fields from the d633 datasets are handled by the script:

Field	Dataset	Horiz. grid	Num. levels
SOILGEO	d633000	~0.281-deg Gaussian	1
SP	d633006	~0.281-deg Gaussian	1
MSL	d633000	0.25-deg Lat-Lon	1
VAR_2T	d633000	0.25-deg Lat-Lon	1
VAR_2D	d633000	0.25-deg Lat-Lon	1
VAR_10U	d633000	0.25-deg Lat-Lon	1
VAR_10V	d633000	0.25-deg Lat-Lon	1
RSN	d633000	0.25-deg Lat-Lon	1
SD	d633000	0.25-deg Lat-Lon	1
LSM	d633000	0.25-deg Lat-Lon	1
SSTK	d633000	0.25-deg Lat-Lon	1
SKT	d633000	0.25-deg Lat-Lon	1
SWVL1	d633000	0.25-deg Lat-Lon	1
SWVL2	d633000	0.25-deg Lat-Lon	1
SWVL3	d633000	0.25-deg Lat-Lon	1
SWVL4	d633000	0.25-deg Lat-Lon	1
STL1	d633000	0.25-deg Lat-Lon	1
STL2	d633000	0.25-deg Lat-Lon	1
STL3	d633000	0.25-deg Lat-Lon	1
STL4	d633000	0.25-deg Lat-Lon	1
CI	d633000	0.25-deg Lat-Lon	1

When model-level ERA5 files are being processed (the default), the following atmospheric fields are handled:

Field	Dataset	Horiz. grid	Num. levels
Q	d633006	~0.281-deg Gaussian	137
T	d633006	~0.281-deg Gaussian	137
U	d633006	~0.281-deg Gaussian	137
V	d633006	~0.281-deg Gaussian	137

Alternatively, if the processing of pressure-level (isobaric) ERA5 files is selected with the -i / --isobaric command-line option, the following atmospheric fields are instead handled:

Field	Dataset	Horiz. grid	Num. levels
Z	d633000	0.25-deg Lat-Lon	37
Q	d633000	0.25-deg Lat-Lon	37
T	d633000	0.25-deg Lat-Lon	37
U	d633000	0.25-deg Lat-Lon	37
V	d633000	0.25-deg Lat-Lon	37

As fields are converted from netCDF to intermediate format, their names are also converted to match WPS and MPAS-A expectations.

Requirements

The era5_to_int.py script requires:

• Python 3.11+
• netCDF4
• NumPy

Usage

The only required command-line argument is the date-time, in YYYY-MM-DD_HH format, of ERA5 model-level files to convert. For example:

era5_to_int.py 2024-05-01_00

Upon successful completion, an intermediate file with the prefix ERA5 is created in the current working directory; for example, ERA5:2024-05-01_00.

With no optional arguments, the script will search known paths on the NWSC Glade filesystem for ERA5 model-level netCDF files. If the -p/--path option is provided with a local path, the script will instead search that local path for ERA5 files that have been downloaded from the NSF NCAR Research Data Archive (RDA) d633 datasets. For example:

era5_to_int.py --path /some/data/directory/era5 2024-05-01_00

Processing a range of times is possible by providing as a second positional argument the date-time until which time records should be converted. For example, to converted the entire month of May 2024:

era5_to_int.py 2024-05-01_00 2024-05-31_18

By default, fields are converted at a six-hourly interval, and a different interval may be specified with a third positional argument. For example, to convert data at a three-hourly interval for the month of May 2024:

era5_to_int.py 2024-05-01_00 2024-05-31_21 3

If only a subset of the standard set of fields is needed, the -v/--variables command-line option may be used to specify this subset as a comma-separated list, without spaces, of the WPS field names. For example:

era5_to_int.py -v LANDSEA,SEAICE,SKINTEMP 2024-01-01_00 2024-01-31_00 24

In this example, intermediate files would be created with only the three fields provided to the -v option, i.e., LANDSEA, SEAICE, and SKINTEMP. None of the other fields that are usually processed by the era5_to_int.py script will be processed.

Note that if a diagnostic variable (e.g, GHT) is needed in the output intermediate files, all of the fields required to compute that diagnostic field (e.g., GEOPT) must be specified in the list supplied to the -v/--variable option.

Usage is provided by running the era5_to_int.py script with the -h/--help argument, which prints the following:

usage: era5_to_int.py [-h] [-p PATH] [-i] [-v VARIABLES] datetime [until_datetime] [interval_hours]

positional arguments:
  datetime              the date-time to convert in YYYY-MM-DD_HH format
  until_datetime        the date-time in YYYY-MM-DD_HH format until which records are converted (Default:
                        datetime)
  interval_hours        the interval in hours between records to be converted (Default: 6)

options:
  -h, --help            show this help message and exit
  -p PATH, --path PATH  the local path to search for ERA5 netCDF files
  -i, --isobaric        use ERA5 pressure-level data rather than model-level data
  -v VARIABLES, --variables VARIABLES
                        a comma-separated list, without spaces, of WPS variable names to process

Supplementary files

Included in this repository is a list of ECMWF vertical level coefficients in the ecmwf_coeffs file. The ecmwf_coeffs file may be used with the WPS calc_ecmwf_p.exe utility program to generate an intermediate file with 3-d pressure, geopotential height, and R.H. fields from ERA5 model-level data.