Improved modeling of cloudy-sky actinic flux using satellite cloud retrievals

Young Hee Ryu, Alma Hodzic, Gael Descombes, Samuel Hall, Patrick Minnis, Douglas Spangenberg, Kirk Ullmann, Sasha Madronich

Research output: Contribution to journalArticlepeer-review


Clouds play a critical role in modulating tropospheric radiation and thus photochemistry. We develop a methodology for calculating the vertical distribution of tropospheric ultraviolet (300–420 nm) actinic fluxes using satellite cloud retrievals and a radiative transfer model. We demonstrate that our approach can accurately reproduce airborne-measured actinic fluxes from the 2013 Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign as a case study. The results show that the actinic flux is reduced below moderately thick clouds with increasing cloud optical depth and can be enhanced by a factor of 2 above clouds. Inside clouds, the actinic flux can be enhanced by up to 2.4 times in the upper part of clouds or reduced up to 10 times in the lower parts of clouds. Our study suggests that the use of satellite-derived actinic fluxes as input to chemistry-transport models can improve the accuracy of photochemistry calculations.

Original languageEnglish
Pages (from-to)1592-1600
Number of pages9
JournalGeophysical Research Letters
Issue number3
Publication statusPublished - 2017 Feb 16

Bibliographical note

Funding Information:
We acknowledge Fred Rose for providing single scattering albedo and asymmetry factor data for the satellite products. Y.-H. Ryu and G. Descombes acknowledge support from NASA-ROSES grant NNX15AE38G. The National Center for Atmospheric Research is sponsored by the National Science Foundation. P. Minnis and D. Spangenberg are supported by the SEAC4RS Project led by Hal Maring and by the NASA Modeling, Analysis, and Prediction (MAP) Program led by David Considine. The TUV model can be downloaded at The satellite cloud data used in this study are available at The in situ airborne data of actinic flux can be requested from Samuel Hall.

Publisher Copyright:
©2017. The Authors.

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Earth and Planetary Sciences(all)


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