The Juelich Rapid Spectral Simulation Code (JURASSIC) is a fast infrared radiative transfer model for the analysis of atmospheric remote sensing measurements.

The Jülich Rapid Spectral Simulation Code (JURASSIC) is a radiative transfer model for simulating infrared radiation in the Earth's atmosphere. It is designed to provide a balance between computational efficiency and physical accuracy, making it suitable for a range of applications in atmospheric and remote sensing research.

JURASSIC applies established spectral approximations together with precomputed lookup tables derived from detailed line-by-line calculations to represent gaseous absorption, emission, and transmission. This approach enables reliable simulations across large datasets or ensembles without the runtime demands of full line-by-line models.

Typical use cases include satellite radiance simulations, sensitivity studies, retrieval algorithm development, and the analysis of atmospheric composition. With its modular design and support for high-performance computing environments, JURASSIC offers a practical tool for studying radiative processes in the middle and upper atmosphere.

JURASSIC provides a comprehensive and efficient framework for infrared radiative transfer simulations, offering key capabilities to support research, operational, and development workflows:

• Efficient radiative transfer approximations: JURASSIC implements the Emissivity Growth Approximation (EGA) and the Curtis–Godson Approximation (CGA) to model infrared radiative transfer. These methods enable rapid yet accurate simulations of atmospheric radiances and transmittances across a broad spectral range.

• High-fidelity spectroscopy via lookup tables: Band transmittances are derived from pre-calculated lookup tables based on detailed line-by-line spectroscopy. This approach maintains spectroscopic accuracy while largely reducing computational cost, making the model suitable for large-scale and near-real-time applications.

• Optimal estimation retrieval framework: In addition to forward modelling, JURASSIC includes an optimal estimation retrieval module for inverse modelling of atmospheric state variables. This enables the derivation of geophysical parameters such as temperature or trace gas volume mixing ratios from observed radiances, providing a complete forward–inverse modelling system within the same framework.

• Flexible configuration and modular design: The model supports customizable spectral bands, instrument configurations, and atmospheric input fields, allowing users to integrate JURASSIC into diverse workflows and existing analysis pipelines.

• Validated against established reference models: The model has undergone extensive benchmarking and intercomparison studies with leading radiative transfer codes such as KOPRA, RFM, and SARTA, ensuring reliable performance and scientific credibility across a wide range of atmospheric conditions.

• Hybrid parallelization for HPC environments: JURASSIC enables hybrid MPI–OpenMP parallelization for highly efficient execution on multicore CPUs and HPC clusters, enabling the processing of large datasets, global simulations, or long time series with excellent scalability.

• Open source and community oriented: JURASSIC is distributed under the GNU General Public License (GPL), fostering transparency, collaboration, and community-driven development within the atmospheric and remote sensing research community.

This documentation describes the installation of JURASSIC on a Linux system. A number of standard tools (gcc, git, make) and software libraries are needed to install JURASSIC. The GNU Scientific Library is required for numerical calculations. A copy of this library can be found in the git repository.

To install JURASSIC, follow these steps:

1. Download JURASSIC

Get the latest or a previous version from the JURASSIC releases page. After downloading, extract the release file:

unzip jurassic-x.y.zip

Alternatively, to get the latest development version, clone the GitHub repository:

git clone https://github.com/slcs-jsc/jurassic.git

2. Install required libraries

The JURASSIC git repository includes a copy of the GNU GSL library that can be compiled and installed using a build script:

cd [jurassic_directory]/libs
./build.sh -a

Alternatively, if you prefer to use existing system libraries, install the dependencies manually.

3. Configure the Makefile

Navigate to the source directory and adjust the Makefile as needed:

cd [jurassic_directory]/src
emacs Makefile

Pay special attention to the following settings:

• Edit the LIBDIR and INCDIR paths to point to the directories where the necessary libraries are located on your system.

• By default, the JURASSIC binaries are linked dynamically. Ensure that the LD_LIBRARY_PATH is properly configured to include the paths to the shared libraries. If you prefer static linking, you can enable it by setting the STATIC flag, which allows you to copy and use the binaries on other machines. However, in some cases, either static or dynamic linking may not be feasible or could cause specific issues.

4. Compile and test the installation

Once the Makefile is configured, compile the code using:

make [-j]

To verify the installation, run the test suite:

make check

This will execute a series of tests sequentially. If any test fails, check the log messages for further details.

JURASSIC provides a project directory for testing the examples and also to store other experiments:

cd [jurassic_directory]/projects

This shows how to run the example for the nadir sounder:

cd nadir ./run.sh

This shows how to run the example for the limb sounder:

cd ../limb ./run.sh

In both examples, we generate an observation geometry file,

cat obs.tab

a standard atmosphere for mid-latitudes,

cat atm.tab

and conduct radiative transfer calculations for two or three detector channels:

cat rad.tab

The output of the simulation is verified by comparing it to reference data. Additionally, gnuplot is used to create plots of the radiance data:

Kernel functions are calculated using a finite difference method:

More detailed information for new users and developers of JURASSIC is collected in the GitHub wiki.

These are the main references for citing the JURASSIC model in scientific publications:

• Baumeister, P. F. and Hoffmann, L.: Fast infrared radiative transfer calculations using graphics processing units: JURASSIC-GPU v2.0, Geosci. Model Dev., 15, 1855–1874, https://doi.org/10.5194/gmd-15-1855-2022, 2022.

• Hoffmann, L., and M. J. Alexander, Retrieval of stratospheric temperatures from Atmospheric Infrared Sounder radiance measurements for gravity wave studies, J. Geophys. Res., 114, D07105, https://doi.org/10.1029/2008JD011241, 2009.

• Hoffmann, L., Kaufmann, M., Spang, R., Müller, R., Remedios, J. J., Moore, D. P., Volk, C. M., von Clarmann, T., and Riese, M.: Envisat MIPAS measurements of CFC-11: retrieval, validation, and climatology, Atmos. Chem. Phys., 8, 3671-3688, https://doi.org/10.5194/acp-8-3671-2008, 2008.

• You can cite the source code of JURASSIC by using the DOI https://doi.org/10.5281/zenodo.4572889. This DOI represents all versions, and will always resolve to the latest one. Specific DOIs for each release of JURASSIC can be found on the zenodo web site.

Please see the citation file for further information.

We are interested in sharing JURASSIC for operational or research applications. Please do not hesitate to contact us, if you have any further questions or need support.

JURASSIC is distributed under the GNU General Public License v3.0.

Dr. Lars Hoffmann

Jülich Supercomputing Centre, Forschungszentrum Jülich

e-mail: l.hoffmann@fz-juelich.de