Obtaining input data

Every tracking experiment requires data, which you might need to download.

  • Meteorogical data

    Typically you will need wind speed in both directions and humidity at multiple (pressure) levels and evaporation and precipitation. If the data comes at model levels, you also need the corresponding pressure.

  • Tagging region

In addition to the time-dependent forcing data, WAM2layers also needs a tagging region. This is used to define the tagging region from where to track moisture. The region can be described by a netCDF file, shapefile, or simple bounding box. For more info see wam2layers.config.Config.tagging_region

Alternatively, on the respository some notebooks are available which tackle more advances tagging region cases.

At this stage, the format of the data is not very strict yet. In the pre-processing step we make sure that the data is ready for tracking. However, if you want to use the pre-processing scripts that come bundled with WAM2layers out-of-the-box, you need to make sure the data follows the same structure as the example data.

Example data

To help you get started, we provide two example cases:

  1. A backward tracking case for an extreme precipitation event over the Eifel region in July 2021.

  2. A forward tracking case of evaporation over the Volta region in Ghana for July and August 1998.

ERA5 data for these regions/periods are available on 4TU (Eiffel; Volta) and can easily be downloaded with WAM2layers:

wam2layers download example-input-eiffel
wam2layers download example-input-volta

File structure

A good file naming system makes it easy to process data for different date ranges, and to automatically read data into the model. For example, for ERA5, we are using the following filenaming structure:

path/to/data/<year>/<month>/ERA5_<year>_<month>_<day><levtype>_<variable>.nc

# for example:
path/to/data/2021/07/ERA5_2021_07_15_ml_q.nc

Here, the <levtype> parameter can be _ml for model levels, _pl for pressure levels, and empty for surface variables. The variable name corresponds to the name of the variable inside the netcdf file, so if our file is called ......tp.nc we expect to find a variable called tp inside this file.

Download scripts

Though it is not our main focus to provide data download utilities, we think it may be helpful to share some commonly used scripts so that not everyone will have to reinvent the wheel. Our download scripts for ERA5 (model and pressure level) data are shipped with the repository and can be found in the scripts folder. These scripts are currently not considered core functionality of WAM2layers and are therefore not part of the command line interface. Please see the docstrings inside these scripts for instructions on how to use them.

Note

It would be nice to collect more data download scripts over time. If you want to share your datascript, we will be happy to help you in adding it to our collection. Please see the contributing chapter of this documentation.