Abstract
AbstractIn calculating solar radiation, climate models make many simplifications, in part to reduce computational cost and enable climate modeling, and in part from lack of understanding of critical atmospheric information. Whether known errors or unknown errors, the community's concern is how these could impact the modeled climate. The simplifications are well known and most have published studies evaluating them, but with individual studies it is difficult to compare. Here, we collect a wide range of such simplifications in either radiative transfer modeling or atmospheric conditions and assess potential errors within a consistent framework on climate‐relevant scales. We build benchmarking capability around a solar heating code (Solar‐J) that doubles as a photolysis code for chemistry and can be readily adapted to consider other errors and uncertainties. The broad classes here include: use of broad wavelength bands to integrate over spectral features; scattering approximations that alter phase function and optical depths for clouds and gases; uncertainty in ice‐cloud optics; treatment of fractional cloud cover including overlap; and variability of ocean surface albedo. We geographically map the errors in W m−2 using a full climate re‐creation for January 2015 from a weather forecasting model. For many approximations assessed here, mean errors are ∼2 W m−2 with greater latitudinal biases and are likely to affect a model's ability to match the current climate state. Combining this work with previous studies, we make priority recommendations for fixing these simplifications based on both the magnitude of error and the ease or computational cost of the fix.
Highlights
The heat from sunlight drives the weather and climate system, the energy in solar photons drives atmospheric chemistry, and the photosynthetically active radiation drives life
One motivation for this study is to evaluate the potential improvements in solar heating rates if more accurate physics or radiative transfer (RT) codes are used, but the overriding motivation is to assess a wide range of approximations and uncertainties within a single climate-relevant framework
We examine additional classes of approximations or uncertainties beyond P2019: examples of the historical improvement in infrared heating codes and the ongoing work at major climate centers (Section 2); the use of bands to integrate over spectral features (Section 3); multiple-scattering approximations that alter the scattering phase function for clouds, aerosols, and gases (Section 4); uncertainty in ice-cloud optics (Section 5); treatment of fractional cloud cover including cloud overlap (Section 6); and approximation of ocean surface albedo (Section 7)
Summary
The heat from sunlight drives the weather and climate system, the energy in solar photons drives atmospheric chemistry, and the photosynthetically active radiation drives life. We examine additional classes of approximations or uncertainties beyond P2019: examples of the historical improvement in infrared heating codes and the ongoing work at major climate centers (Section 2); the use of bands to integrate over spectral features (Section 3); multiple-scattering approximations that alter the scattering phase function for clouds, aerosols, and gases (Section 4); uncertainty in ice-cloud optics (Section 5); treatment of fractional cloud cover including cloud overlap (Section 6); and approximation of ocean surface albedo (Section 7) Each one of these sections has been the focus of major research studies that we briefly review. Errors on this scale are important and must eventually be addressed
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.