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Atmos. Chem. Phys. Discuss., 11, 3321-3354, 2011
www.atmos-chem-phys-discuss.net/11/3321/2011/ doi:10.5194/acpd-11-3321-2011 © Author(s) 2011. This work is distributed under the Creative Commons Attribution 3.0 License. |
Ultraviolet actinic flux in clear and cloudy atmospheres: model calculations and aircraft-based measurements
1INFIQC-CONICET, Departamento de Físico Química, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Centro Láser de Ciencias Moleculares, 5000 Córdoba, Argentina
2Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado, USA
Abstract. Ultraviolet (UV) actinic fluxes measured with two Scanning Actinic Flux Spectroradiometers (SAFS) aboard the NASA DC-8 aircraft are compared with the Tropospheric Ultraviolet-Visible (TUV) model. The observations from 17 days in July–August 2004 (INTEX-NA field campaign) span a wide range of latitudes (27.5° N–53.0° N), longitudes (45.1° W–139.5° W), altitudes (0.1–11.9 km), ozone columns (285.4–352.7 DU), and solar zenith angles (1.7°–85°). Both cloudy and cloud-free conditions were encountered. For cloud-free conditions, the ratio of observed to clear-sky-model actinic flux (integrated from 298 to 422 nm) is 1.01±0.04, i.e. in good agreement with observations. The agreement improves to 1.00±0.03 for the down-welling component under clear sky conditions. In the presence of clouds, both down-welling and up-welling components show reductions or enhancements from clear sky values, depending on the position of the airplane relative to clouds. The correlations between up-welling and down-welling deviations are well reproduced with sensitivity studies using the TUV model, and are understood qualitatively with a simple conceptual model. This analysis of actinic flux observations illustrates opportunities for future evaluations of photolysis rates in three-dimensional chemistry-transport models.
Citation: Palancar, G. G., Shetter, R. E., Hall, S. R., Toselli, B. M., and Madronich, S.: Ultraviolet actinic flux in clear and cloudy atmospheres: model calculations and aircraft-based measurements, Atmos. Chem. Phys. Discuss., 11, 3321-3354, doi:10.5194/acpd-11-3321-2011, 2011.