ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-3-377-2003 Twilight tropospheric and stratospheric photodissociation rates derived from balloon borne radiation measurements Kylling A. 1 Danielsen T. 1 Blumthaler M. 2 Schreder J. 2 Johnsen B. 3 Norwegian Institute for Air Research, Kjeller, Norway Institute of Medical Physics, University of Innsbruck, Innsbruck, Austria Norwegian Radiation Protection Authority, Oslo, Norway 03 04 2003 3 2 377 385 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/3/377/2003/acp-3-377-2003.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/3/377/2003/acp-3-377-2003.pdf

A new ligthweight multichannel moderate bandwidth filter instrument designed to be flown on balloons, is described. The instrument measures the radiation field within the short UV (center wavelength at 312 nm) and long UV (center wavelength at 340 nm). The angular and spectral characteristics of the instrument are discussed and the calibration procedure outlined. Measurements made during a stratospheric balloon flight at twilight conditions from Gap-Tallard, France, are presented and compared with state-of-the-art radiative transfer model simulations. The model simulations and the measurements agree within ±10% (±20%) for solar zenith angles smaller than 93° (90°) for the 340 (312) nm channel. Based on the model simulations of the measured radiation, actinic flux spectra are reconstructed. These are used to calculate various photodissociation rates.