Posted on October 17, 2023 (Updated on September 4, 2025)

Converting NetCDF Files to WRF Input Format: A Comprehensive Guide for Earth Scientists

Software & Programming

Wrangling NetCDF Files into WRF: A Down-to-Earth Guide for Earth Scientists

So, you’re an earth scientist diving into the world of the Weather Research and Forecasting (WRF) model? Awesome! But let’s face it, getting your data ready for WRF can feel like wrestling an octopus, especially when you’re dealing with NetCDF files. These files, while fantastic for storing scientific data, aren’t exactly WRF’s native language. Think of it as trying to order a pizza in Klingon – it’s gonna take some translation. That’s where the WRF Preprocessing System, or WPS, comes in. It’s the Rosetta Stone that helps you convert your NetCDF data into something WRF can actually understand.

The WPS is basically a suite of programs designed to prep your data for WRF, particularly when you’re simulating real-world weather scenarios. It’s got three main players: Geogrid, Ungrib, and Metgrid. Geogrid is like your mapmaker, defining the area you’re simulating and slapping all the static geographical info – like mountains and land use – onto your model grid. Ungrib? Well, normally it’s the guy who wrangles data from GRIB files. But we’ll get to that little detour in a minute. And finally, Metgrid takes all that meteorological data and smooshes it onto the grid Geogrid created.

Now, here’s the thing: WPS is designed to play nice with GRIB files. But a lot of data these days comes in NetCDF format. Can we still use it? Absolutely! It just takes a few extra steps. Think of it as adding a little hot sauce to your pizza – it enhances the flavor, or in this case, the functionality.

Alright, let’s get down to the nitty-gritty. How do we actually convert those NetCDF files into something WRF can sink its teeth into?

  • First things first: Get WRF and WPS: Head over to the official website, grab the source code, and follow the instructions to get everything compiled on your system. It’s a bit like building a LEGO set – follow the instructions, and you’ll be golden. The WPS build is pretty similar to WRF’s, so if you’ve done WRF, you’re halfway there.

  • Point WPS to NetCDF: Make sure WRF and WPS can actually find your NetCDF libraries. This usually involves setting environment variables. On my system, I had to set the NETCDF variable to the right directory. It’s like telling your GPS where to find your house.

  • Geogrid is your friend: Start with Geogrid. This guy defines your simulation area. The output from Geogrid is already in a WRF-friendly NetCDF format (geo_em.d0*.nc). Just make sure the geog_data_path and geog_data_res variables in your namelist.wps file are pointing to the right place – where all your static geographical data lives.

  • The Ungrib detour (and how to avoid it): Okay, normally ungrib.exe is used to process GRIB files. But we’re rocking NetCDF, remember? So, we need to be a little creative. You’ve got a few options here:

    • The Intermediate Route: metgrid.exe reads data in an intermediate format. Since WPS only converts from GRIB to this format, you might need to roll up your sleeves and write your own converter from NetCDF. It’s a bit of coding, but hey, you’re an earth scientist – you’re smart!
    • Direct met_em Manipulation: Skip ungrib altogether and dive straight into modifying the met_em.d0* files. This is where tools like NCO (NetCDF Operators) or NCL (NCAR Command Language) become your best friends. It’s like being a surgeon, but with data.
    • NCO to the Rescue: Use the NetCDF Operators (NCO) toolkit to extract the variables you need from your NetCDF file and save them in a format that Metgrid can handle.

  • NCL Magic for met_em Files: NCL is your friend when it comes to tweaking NetCDF files, including the “geo_em.d0*.nc” file. Here’s a snippet to give you an idea:

    ncl

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