Ultraviolet actinic flux in clear and cloudy atmospheres: model calculations and aircraft-based measurements
Author:
Palancar G. G.,Shetter R. E.,Hall S. R.,Toselli B. M.,Madronich S.
Abstract
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.
Publisher
Copernicus GmbH
Reference44 articles.
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