Extending the Atmospheric Radiative Transfer Simulator (ARTS) to Shortwave Radiation

Abstract Atmospheric Radiative Transfer Simulator (ARTS) is an open source general purpose radiative transfer model used for a wide range of applications from remote sensing to the interaction of climate and radiation. In the past, it was confined to the microwave and infrared spectral range, as ARTS could not simulate the interaction of solar radiation in the atmosphere. Here we close this gap and extend ARTS to the shortwave range. We introduce a solar source that can be used as a collimated beam source and as background source allowing to resolve the finite solar disc. Additionally, we implemented a new clear sky solver that supports collimated beam sources and solar background sources, and updated the ARTS DISORT interface to utilize DISORT's capability for collimated beam sources. This allows consistent line‐by‐line radiative transfer simulations from the microwave to the ultraviolet range with ARTS. We evaluated the shortwave capabilities of ARTS by comparing it with LBLRTM for clear sky simulations. The root mean square deviation between them is 0.70 Wm−2 for the upward flux at top of the atmosphere and 0.66 Wm−2 for the downward flux at the surface. Simulations of a sunrise as seen from space, of satellite observations and of full spectrum all sky radiative flux illustrate the new capabilities. With the new features, ARTS can be used for a wide range of new applications.