Coupling GEOS-Chem with RRTMG

The GEOS-Chem model with online radiative transfer calculations (referred to as GCRT) was developed to allow GEOS-Chem users to produce gas and aerosol direct radiative effect (DRE) output. This alternative to offline coupling allows better temporal resolution in the RT calculations and provides a consist platform for GEOS-Chem users with the reliable radiative transfer package RRTMG.

Most of the added code is 'transparent', therefore GEOS-Chem model can still be run with the radiation code switched off. The optical properties are calculated at multiple wavelengths so the user is no longer restricted to 550nm as default, or indeed a single wavelength, so there are associated changes regardless of whether the radiative code is invoked. However, these cause negligible slow down (the model is actually slightly faster).

This wiki explains the key changes, why they were chosen, and links to the documentation for getting started running the model and digging deeper into the changes and the auxiliary files required.