PyRADS is the Python line-by-line RADiation model for planetary atmosphereS. PyRADS is a radiation code that can provide line-by-line spectral resolution, yet is written in Python and so is flexible enough to be useful in teaching.

For Earth-like atmospheres, PyRADS currently uses HITRAN 2016 line lists (http://hitran.org/) and the MTCKD continuum model (http://rtweb.aer.com/continuum_frame.html).

Looking for a version of PyRADS that can deal with shortwave radiation (scattering)? https://github.com/ddbkoll/PyRADS-shortwave

References:

(1) Koll & Cronin, 2018, https://doi.org/10.1073/pnas.1809868115.

1. Download to your own computer.

2. [optional] Install the required libraries using conda:

• cd $PyRADS
• conda env create -f environment.yml
• conda activate pyrads

3. Manually compile the MTCKD model:

• cd $PyRADS/DATA/MT_CKD_continuum/cntnm.H2O_N2/build
• (on a Mac if you are using gfortran installed with conda) make -f make_cntnm osxGNUCONDAdbl
• (on a Mac otherwise) make -f make_cntnm osxGNUdbl

4. Run test scripts

To compute outgoing longwave radiation (OLR) in W/m2 for a given surface temperature:

• cd $PyRADS/Test01.olr
• python compute_olr_h2o.py

To compute OLRs for a set of surface temperatures and save the resulting output to txt:

• cd $PyRADS/Test02.runaway
• python compute_olr_h2o.01.100RH.py

• Resolution in test scripts was chosen for relative speed, not accuracy. For research-grade output and model intercomparisons, vertical and spectral resolution need to be increased. For some reference values, see Methods in Koll & Cronin (2018).
• 'environment.yml' assumes you're using a Mac. For Linux, change the gfortran compiler.
• If you're using conda, don't forget to type ``conda activate pyrads'' each time before using PyRADS.
• The current version of PyRADS has a silent bug when using numba computing line crosssections for multiple species (e.g., H2O CO2 lines). By default numba is currently disabled. Until the bug is fixed don't use PyRADS numba without additional validation.
• Dec 2021: PyRADS allows an optional Voigt line profile. The main impact is for opacity calculations at low pressures, where the Lorentz line approximation breaks down. The current Voigt implementation is 3-4x slower than Lorentz lines. To switch line profiles, see OpticalThickness.py.
• Jan 2022: To compute CO2 radiative forcing for Earth-ish climates accurately, suggested spectral resolution is 0.01 cm-1. The impact of Voigt vs Lorentz line shape also becomes much less important at high spectral resolution.

Python 3 with numpy and scipy.

For faster calculations: numba.

For the MTCKD continuum model: gmake and gfortran.

PyRADS makes use of HITRAN 2016 line lists (http://hitran.org/), AER's MTCKD continuum model (http://rtweb.aer.com/continuum_frame.html), and the PyTran script published by Ray Pierrehumbert as part of the courseware for "Principles of Planetary Climates" (https://geosci.uchicago.edu/~rtp1/PrinciplesPlanetaryClimate/). Brian Rose (http://www.atmos.albany.edu/facstaff/brose/) and Andrew Williams (https://github.com/AndrewWilliams3142) have improved the code.

PyRADS v1.0 is also available on .