Photolysis Rates in Correlated Overlapping Cloud Fields: Cloud-J 7.3c

TitlePhotolysis Rates in Correlated Overlapping Cloud Fields: Cloud-J 7.3c
Publication TypeJournal Article
Year of Publication2015
JournalGeosci. Model Dev.
Volume8
Pages2587–2595
Date Published08/2015
Abstract / Summary

A new approach for modeling photolysis rates (J values) in atmospheres with fractional cloud cover has been developed and is implemented as Cloud-J – a multiscattering eight-stream radiative transfer model for solar radiation based on Fast-J. Using observations of the vertical correlation of cloud layers, Cloud-J 7.3c provides a practical and accurate method for modeling atmospheric chemistry.  The combination of the new maximum-correlated cloud groups with the integration over all cloud combinations by four quadrature atmospheres produces mean J values in an atmospheric column with root mean square (rms) errors of 4% or less compared with 10–20% errors using simpler approximations. Cloud-J is practical for chemistry–climate models, requiring only an average of 2.8 Fast-J calls per atmosphere vs. hundreds of calls with the correlated cloud groups, or 1 call with the simplest cloud approximations.  Another improvement in modeling J values, the treatment of volatile organic compounds with pressure-dependent cross sections, is also incorporated into Cloud-J.

DOI10.5194/gmd-8-2587-2015
Journal: Geosci. Model Dev.
Year of Publication: 2015
Volume: 8
Pages: 2587–2595
Date Published: 08/2015

A new approach for modeling photolysis rates (J values) in atmospheres with fractional cloud cover has been developed and is implemented as Cloud-J – a multiscattering eight-stream radiative transfer model for solar radiation based on Fast-J. Using observations of the vertical correlation of cloud layers, Cloud-J 7.3c provides a practical and accurate method for modeling atmospheric chemistry.  The combination of the new maximum-correlated cloud groups with the integration over all cloud combinations by four quadrature atmospheres produces mean J values in an atmospheric column with root mean square (rms) errors of 4% or less compared with 10–20% errors using simpler approximations. Cloud-J is practical for chemistry–climate models, requiring only an average of 2.8 Fast-J calls per atmosphere vs. hundreds of calls with the correlated cloud groups, or 1 call with the simplest cloud approximations.  Another improvement in modeling J values, the treatment of volatile organic compounds with pressure-dependent cross sections, is also incorporated into Cloud-J.

DOI: 10.5194/gmd-8-2587-2015
Citation:
Prather, MJ.  2015.  "Photolysis Rates in Correlated Overlapping Cloud Fields: Cloud-J 7.3c."  Geosci. Model Dev. 8: 2587–2595.  https://doi.org/10.5194/gmd-8-2587-2015.