Spektrale aktinische Flussdichten und Photolysefrequenzen – Untersuchungen in der atmosphärischen Grenzschicht und der freien Troposphäre

• Main Author: Lohse, Insa Mareike
• Format: Doctoral or Postdoctoral Thesis
• Language: German
• Published: Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag 2015
• Subjects: narval
• Online Access: https://juser.fz-juelich.de/record/256276; https://juser.fz-juelich.de/search?p=id:%22FZJ-2015-06240%22

Solar UV radiation is driving atmospheric photochemistry because the photolysis of atmospheric trace gases yields highly reactive atoms or radicals. Thus, trace gas concentrations as well as accurate photolysis frequencies are needed to understand atmospheric photochemical processes. Especially under varying cloud conditions, measurements can often not be replaced by radiative transfer calculations with sufficient accuracy. In this work, airborne measurements of the separate upwelling and downwelling components of the actinic flux densities (280–650 nm) were performed with CCD-spectroradiometers. For accurate UV measurements a thorough treatment of stray light was applied for the single monochromator based array spectrometers. Moreover, the angular sensitivities of the optical receivers were determined to analyze their influence under various atmospheric conditions using radiative transfer calculations of realistic atmospheric radiance distributions. Corresponding correction factors in the range of 5% were derived. The overall performance was tested on the ground by in-field comparisons with a doublemonochromator reference system and found to have maximum deviations of 7%. Measurements of the spectral actinic flux density were performed aboard Zeppelin NT in the atmospheric boundary layer during the PEGASOS campaign 2012/13 over different parts of Europe. Moreover the research aircraft HALO was used during the NARVAL campaign 2013/14 for measurements in the upper troposphere and the lower stratosphere over the Atlantic Ocean. Typical Zeppelin flight heights ranged from 100m to 900m and flights were therefore always performed below possible cloud layers. Thus the measurements were influenced by potentially overlaying clouds and a small upwelling part of radiation. Radiative transfer calculations of the downwelling component under the assumption of clearsky conditions showed good agreement with the maximum values of the measurements. The upwelling component of the spectral actinic flux density was unexpectedly ...