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Comparison of measured and modeled stratospheric UV/Visible actinic fluxes at large solar zenith angles
Author(s) -
Bösch H.,
CamyPeyret C.,
Chipperfield M.,
Fitzenberger R.,
Harder H.,
Schiller C.,
Schneider M.,
Trautmann T.,
Pfeilsticker K.
Publication year - 2001
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2000gl012134
Subject(s) - zenith , solar zenith angle , stratosphere , irradiance , occultation , radiative transfer , environmental science , atmospheric sciences , atmospheric radiative transfer codes , azimuth , optics , physics , astrophysics
Measured and modeled stratospheric filter sensitivity weighted ultraviolet/visible (UV/vis) actinic fluxes—approximating the NO 2 photolysis rate coefficients (j NO 2 )— are compared. The measurements were performed with two calibrated 2π‐actinometers assembled on the azimuth angle‐controlled LPMA/DOAS (Laboratoire de Physique Moléculaire et Applications/Differential Optical Absorption Spectroscopy) gondola during a series of balloon flights. Since the actinometer's spectral sensitivity curve did not exactly match the actinic spectrum of NO 2 and the skylight's spectrum shape changes with atmospheric height and solar illumination, only proxies (proxy‐ )j NO 2 rather than true j NO 2 values were monitored during balloon ascents (0–30 km) for solar zenith angle (SZA) 75° < SZA < 86°, and at balloon float altitude during solar occultation (86° < SZA < 95°). The measured direct and diffuse total proxy ‐j NO 2 values compare excellently with radiative transfer (RT) modeling. That finding allows us to rule out uncertainties in computing UV/vis actinic fluxes as a significant factor in the still insufficient modeling of stratospheric NO 2 at large SZAs.