era5_to_int

A simple utility for converting ERA5 netCDF files to the WPS intermediate format.

This has been packaged up and slightly modified from the original NCAR era5_to_int scripts. Huge thanks to NCAR and to Michael Duda and Anthony Islas for writing the scripts!

Installation

You can install the command line utility in a variety of ways. One of the easiest and most common is to use pipx:

pipx install era5_to_int

Overview

The era5_to_int utility converts ERA5 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 required command-line arguments are the path to the local files and the start and end datetimes of ERA5 files to convert. For example:

era5_to_int /root/path/to/era5/ 2024-05-01_00 2024-05-02_00

or if you're using a different time format, then you'll need to put quotes around the datetimes:

era5_to_int /root/path/to/era5/ "2024-05-01 00" "2024-05-02 00"

The directory structure must be the same as NCAR's ERA5 AWS S3 bucket. This is the recommended place to download the ERA5 data since it's free and fast.

Conversion of a range of datetimes 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:

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

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

Downloading and spatial clipping the ERA5 data

This command line utility isn't very helpful if you don't have the ERA5 data. There is a docker image made specifically to download the ERA5 data from the AWS S3 bucket maintained by NCAR. Then the container will clip the global files to a user-defined region to substantially shrink the files. It will save the clipped files to a directory or optionally upload it to another S3 system defined by the user.

You can find the github repo here: https://github.com/envlib/era5-download

It will download all of the files necessary to run the era5_to_int utility.

Usage

The required command-line arguments are the path to the local files and the start and end datetimes of ERA5 files to convert. For example:

era5_to_int /root/path/to/era5/ 2024-05-01_00 2024-05-02_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.

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

era5_to_int -h 3 /root/path/to/era5/ 2024-05-01_00 2024-05-02_00

Also by default, all variables required to run WRF are processed. If only a selection of variables is required, then use the --variables option:

era5_to_int --variables LANDSEA,SEAICE,SKINTEMP /root/path/to/era5/ 2024-05-01_00 2024-05-02_00

If you want all variables except a few, use --skip-vars (composes with --variables if both are given). Skipped variables do not need their ERA5 NetCDF files on disk, so this is useful when sourcing a field from elsewhere — for example, providing SST and sea ice from a higher-resolution product:

era5_to_int --skip-vars SST,SEAICE /root/path/to/era5/ 2024-05-01_00 2024-05-02_00

Usage help is provided by running the era5_to_int with the --help argument.