Abstract
Abstract. In this study, we compare measured and simulated O4 absorptions for conditions of extremely low aerosol optical depth (between 0.034 to 0.056 at 360 nm) on one day during a ship cruise in the tropical Atlantic. For such conditions, the uncertainties related to imperfect knowledge of aerosol properties do not significantly affect the comparison results. We find that the simulations underestimate the measurements by 15 % to 20 %. Even for simulations without any aerosols, the measured O4 absorptions are still systematically higher than the simulation results. The observed discrepancies cannot be explained by uncertainties of the measurements and simulations and thus indicate a fundamental inconsistency between simulations and measurements.
Highlights
Remote sensing measurements of the atmospheric absorption of the oxygen dimer (O2)2 are often used to derive properties of aerosols and clouds
Several studies found that a scaling factor (SF < 1) had to be applied to the observed atmospheric O4 absorptions in order to bring them into agreement with radiative transfer simulations (e.g. Wagner et al, 2009; Clémer et al, 2010)
One important result of the comparison was that for all measurements, the observed O4 absorption was higher than the simulation results for an atmosphere without aerosols
Summary
Remote sensing measurements of the atmospheric absorption of the oxygen dimer (O2) are often used to derive properties of aerosols and clouds. Several studies found that a scaling factor (SF < 1) had to be applied to the observed atmospheric O4 absorptions in order to bring them into agreement with radiative transfer simulations One major difficulty in the quantitative interpretation of these comparisons is that usually the atmospheric aerosol properties are not well known (e.g. the vertical extinction profile and/or the optical properties). Even if they were known, it is still a challenge to accurately represent them in atmospheric radiative transfer simulations. Are less important for the interpretation of the comparison results than in previous studies because of the low AOD, and we find large discrepancies between the measured and simulated O4 absorptions.
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