era5-s3-dl 0.2.1

A utility for downloading and subsetting ERA5 data from NCAR S3

era5-s3-dl

CLI tool for downloading ERA5 reanalysis data from NCAR's AWS S3 archive, clipping files to geographic bounds, and uploading the results to a remote destination. As of this writing, the total size of the ERA5 global files is 236 TB -- you will definitely want to clip to your region.

For each file, the tool: downloads from the NCAR source via rclone, clips to lat/lon bounds via ncks (converting to NetCDF-4 with compression), and uploads the clipped file to a configured remote destination.

Prerequisites

• Python >= 3.10
• ncks (part of NCO) must be installed separately for NetCDF clipping

Installation

pipx install era5_s3_dl

With optional Sentry error tracking (used in Docker deployment):

pipx install era5_s3_dl[sentry]

Docker

The Docker image includes ncks and installs the tool with the Sentry extra. Modify parameters.toml and docker-compose.yml, then run:

docker-compose up -d
docker-compose logs -f

The docker-compose.yml mounts your parameters.toml into the container and maps an output volume:

volumes:
    - "./parameters.toml:/parameters.toml"
    - "./output:/data/output"

Configuration

Copy parameters_example.toml to parameters.toml and edit it. The TOML file is the primary configuration mechanism -- all settings live here, and select values can be overridden via CLI options.

TOML sections

Root-level settings:

Key	Type	Default	Description
n_tasks	int	8	Number of parallel download workers
check_target	bool	true	Check remote for existing files before downloading (skips duplicates)
work_dir	string	(temp dir)	Working directory for intermediate files. Creates download/ and clipped/ subdirs within it. If not set, uses a temporary directory that is cleaned up on completion.
preset	string		Variable preset (e.g. "wrf", "all"). Required unless variables is set.
variables	string		Comma-separated NetCDF variable names to download (case insensitive). Combined with preset if both set.
skip_vars	string		Comma-separated NetCDF variable names to exclude (case insensitive). Applied after preset + variables.

[dates] -- Date range for files to download:

[dates]
start_date = "2020-01-01"
end_date = "2024-12-31"

[bounds] -- Geographic clipping bounds (longitude/latitude):

[bounds]
min_lon = 145
max_lon = 195
min_lat = -60
max_lat = -20

[source] -- rclone config for the NCAR ERA5 source bucket. The default points to the public nsf-ncar-era5 bucket on AWS:

[source]
type = 's3'
provider = 'AWS'
env_auth = 'false'
region = 'us-west-2'
path = 'nsf-ncar-era5/'

[remote] -- rclone config for the upload destination. Can be S3 or a local path. Optional for --list-only mode:

# S3 example:
[remote]
type = 's3'
provider = 'Mega'
endpoint = 'https://s3.example.com'
access_key_id = ''
secret_access_key = ''
path = '/data/ncar/era5/'

# Local example (use with Docker volume mount):
[remote]
type = 'local'
path = '/data/output'

[sentry] (optional) -- Sentry error tracking. Requires the sentry extra to be installed:

[sentry]
dsn = ''
tags = {}

Variable Selection

You must specify which ERA5 variables to download using --preset and/or --variables.

Presets select a predefined group of variables:

• wrf -- the 26 variables required for WRF model initialization
• all -- all 92 available ERA5 variables

Variables are specified by their NetCDF variable name (case insensitive). The full catalog is in era5_dl/era5_variables.json. Examples: SP, VAR_2T, Z, CAPE, U, V.

When both --preset and --variables are given, the variables are combined (union).

Skip-vars (--skip-vars) removes variables after --preset and --variables are resolved. Useful when you want a preset minus a few fields — e.g. WRF inputs but with SST and sea ice coming from a different dataset.

# Download WRF variables only
era5_dl parameters.toml --preset wrf

# Download just surface pressure and 2m temperature
era5_dl parameters.toml --variables sp,var_2t

# Download WRF variables plus CAPE
era5_dl parameters.toml --preset wrf --variables cape

# Download WRF variables but skip SST and sea ice (sourcing them elsewhere)
era5_dl parameters.toml --preset wrf --skip-vars sstk,ci

# List all available files without downloading
era5_dl parameters.toml --preset all --list-only

Usage

Basic invocation with a parameters file:

era5_dl parameters.toml --preset wrf

Override specific TOML values via CLI options:

era5_dl parameters.toml --preset wrf -s 2024-01-01 -e 2024-12-31 -n 4
era5_dl parameters.toml --preset wrf --min-lon 160 --max-lon 180 --no-check-target

List matching files without downloading (does not require [remote] config):

era5_dl parameters.toml --preset wrf --list-only

See all options:

era5_dl --help

CLI Options

All options are optional and override the corresponding value in the parameters TOML file.

Option	Short	Type	Overrides
--n-tasks	-n	int	n_tasks
--work-dir	-w	path	work_dir
--check-target / --no-check-target		bool	check_target
--start-date	-s	text	dates.start_date
--end-date	-e	text	dates.end_date
--min-lon		float	bounds.min_lon
--max-lon		float	bounds.max_lon
--min-lat		float	bounds.min_lat
--max-lat		float	bounds.max_lat
--preset	-p	text	preset
--variables	-v	text	variables
--skip-vars		text	skip_vars
--list-only	-l	flag	Query and list files only, skip download