Reading MERRA2 Data Using Kerchunk Reference File

Many of NASA’s current and legacy data collections are archive in netCDF4 format. By itself, netCDF4 are not cloud optimized and reading these files can take as long from a personal/local work environment as it takes to read the data from a working environment deployed in the cloud. Using Kerchunk, we can treat these files as cloud optimized assets by creating metadata json file describing existing netCDF4 files, their chunks, and where to access them. The json reference files can be read in using Zarr and Xarray for efficient reads and fast processing.


1. AWS instance running in us-west-2

NASA Earthdata Cloud data in S3 can be directly accessed via temporary credentials; this access is limited to requests made within the US West (Oregon) (code: us-west-2) AWS region.

2. Earthdata Login

An Earthdata Login account is required to access data, as well as discover restricted data, from the NASA Earthdata system. Thus, to access NASA data, you need Earthdata Login. Please visit to register and manage your Earthdata Login account. This account is free to create and only takes a moment to set up.

3. netrc File

You will need a netrc file containing your NASA Earthdata Login credentials in order to execute the notebooks. A netrc file can be created manually within text editor and saved to your home directory. For additional information see: Authentication for NASA Earthdata.

Import required packages

import requests
import xarray as xr
import ujson
import s3fs
import fsspec
from tqdm import tqdm
from glob import glob
import os
import pathlib
import hvplot.xarray

from kerchunk.hdf import SingleHdf5ToZarr
from kerchunk.combine import MultiZarrToZarr

# The xarray produced from the reference file throws a SerializationWarning for each variable. Will need to explore why
import warnings