PyFLEXTRKR: a Flexible Feature Tracking Python Software for Convective Cloud Analysis

1. Introduction

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The Python FLEXible object TRacKeR (PyFLEXTRKR) is a flexible atmospheric feature tracking software package. The software can track any 2D objects and handle merging and splitting explicitly. PyFLEXTRKR has specific capabilities to track convective clouds from a variety of observations and model simulations, including: 1) individual convective cells, and 2) mesoscale convective systems (MCSs) using radar, satellite, and model data. The package has scalable parallelization options and has been optimized to work on large datasets including global kilometer-scale data.

For a more detailed user guide, click this link.

2. Input Data Requirements

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PyFLEXTRKR works with netCDF files using Xarray's capability to handle N-dimension arrays of gridded data. Currently, PyFLEXTRKR supports tracking:

1. Individual convective cells using radar reflectivity data [Feng et al. (2022), MWR];
2. MCSs using infrared brightness temperature (Tb) data from geostationary satellites, or outgoing longwave radiation (OLR) data from model simulations, with optional collocated precipitation data [Feng et al. (2021), JGR] or 3D radar reflectivity data [Feng et al. (2018) JAMES; Feng et al. (2019), JCLI] to identify robust MCSs;
3. Generic 2D objects defined by customizable feature identification functions.

The input data must contain at least 3 dimensions: time, y, x, with corresponding coordinates of time, latitude, longitude. The latitude and longitude coordinates can be either 1D or 2D. But the data must be on a fixed 2D grid (any projection is fine) since PyFLEXTRKR only supports tracking data on 2D arrays. Irregular grids such as those in E3SM or MPAS model must first be regridded to a regular grid before tracking. Additional variable names and coordinate names are specified in the config file. See user guide for more details in preparing the input dataset.

3. Installing PyFLEXTRKR

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PyFLEXTRKR requires Python 3.6 and above. Support for Python 3.8 and lower has reached end-of-life so it is recommended to use Python 3.9 or higher.

Install via Conda

The easiest way to install the most recent version of PyFLEXTRKR is via conda through the conda-forge channel:

conda install pyflextrkr -c conda-forge

This will also install all dependencies and should be sufficient for most users. You can update the installation by:

conda update pyflextrkr -c conda-forge

Install from source via Github

Clone PyFLEXTRKR to your local computer (e.g., /PyFLEXTRKR):

bash git clone https://github.com/FlexTRKR/PyFLEXTRKR.git

Go to that directory:

bash cd /PyFLEXTRKR

Use the included environment.yml file to create a Conda virtual environment, make sure you change conda_env_dir to where your conda environments are installed:

bash conda env create -f environment.yml --prefix /conda_env_dir/flextrkr

or ...

bash conda create -n flextrkr -c conda-forge --file requirements.txt

Pro Tips: using mamba to create the virtual environment is much faster:

bash mamba env create -f environment.yml --prefix /conda_env_dir/flextrkr

After setting up the Conda virtual environment, activate it with:

bash conda activate flextrkr

Then install the package with:

bash pip install -e .

Any changes to the source code will be reflected in the running version.

4. Example Data and Runscripts

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Several scripts are provided to download example input data, run tracking, and produce visualizations of the tracking results below:

1. Convective cell tracking from 500 m gridded NEXRAD radar data

2. Convective cell tracking from 500 m gridded ARM CSAPR radar data

1. MCS tracking from 10 km GPM IMERG Tb + precipitation data

2. MCS tracking from 4 km WRF Tb + precipitation data

3. MCS tracking from 4 km WRF Tb + 3D reflectivity data

4. MCS tracking from 25 km model OLR + precipitation data

1. Generic feature tracking (e.g., 500 hPa geopotential height anomaly)

To run these demo scripts, download the script, modify the dir_demo in the script to a directory on your computer to store the sample data, and run the following command:

bash bash demo_cell_nexrad.sh

The demo script downloads and untar the sample data, runs the tracking code, and generates visualizations. Once the demo script finishes running, a sub-directory within the dir_demo named quicklooks_trackpaths will be created that contains quicklook visualization of the tracking results, as shown in the example animations above.

5. Running PyFLEXTRKR

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To run the code, type the following in the command line:

Activate PyFLEXTRKR virtual environment:

bash conda activate flextrkr

Run PyFLEXTRKR:

bash python ../runscripts/run_celltracking.py ./config/config_nexrad500m_example.yml

bash python ./runscripts/run_mcs_tbpf.py ./config/config_wrf4km_mcs_tbpf_example.yml

Example run scripts and config files are in the highlighted directories:

6. Statistical Analysis

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A Gallery of Statistical Analysis that can be applied to the tracking outputs is provided. Below are some examples.

7. References

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Feng, Z., Hardin, J., Barnes, H. C., Li, J., Leung, L. R., Varble, A., & Zhang, Z. (2023). PyFLEXTRKR: a flexible feature tracking Python software for convective cloud analysis. Geosci. Model Dev., 16(10), 2753-2776. https://doi.org/10.5194/gmd-16-2753-2023

Feng, Z., Varble, A., Hardin, J., Marquis, J., Hunzinger, A., Zhang, Z., & Thieman, M. (2022). Deep Convection Initiation, Growth, and Environments in the Complex Terrain of Central Argentina during CACTI. Monthly Weather Review, 150(5), 1135-1155. https://doi.org/10.1175/MWR-D-21-0237.1

Feng, Z., Leung, L. R., Liu, N., Wang, J., Houze, R. A., Li, J., et al. (2021). A Global High‐Resolution Mesoscale Convective System Database Using Satellite‐Derived Cloud Tops, Surface Precipitation, and Tracking. Journal of Geophysical Research: Atmospheres, 126(8). https://doi.org/10.1029/2020JD034202

Feng, Z., Leung, L. R., Houze, R. A., Hagos, S., Hardin, J., Yang, Q., et al. (2018). Structure and Evolution of Mesoscale Convective Systems: Sensitivity to Cloud Microphysics in Convection-Permitting Simulations Over the United States. Journal of Advances in Modeling Earth Systems, 10(7), 1470-1494. https://doi.org/10.1029/2018MS001305

Feng, Z., Houze, R. A., Leung, L. R., Song, F., Hardin, J. C., Wang, J., et al. (2019). Spatiotemporal Characteristics and Large-scale Environments of Mesoscale Convective Systems East of the Rocky Mountains. Journal of Climate, 32(21), 7303-7328. https://doi.org/10.1175/JCLI-D-19-0137.1

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