Intercomparison exercise between different radiative transfer models used for the interpretation of ground-based zenith-sky and multi-axis DOAS observations

Abstract

Abstract. We present the results of an intercomparison exercise between six different radiative transfer (RT) models carried out in the framework of QUILT, an EU funded project based on the exploitation of the Network for the Detection of Stratospheric Change (NDSC). RT modelling is an important step in the interpretation of Differential Optical Absorption Spectroscopy (DOAS) observations. It allows the conversion of slant column densities (SCDs) into vertical column densities (VCDs) using calculated air mass factors (AMFs). The originality of our study resides in comparing SCD simulations in multi-axis (MAX) geometry (trace gases: NO 2 and HCHO) and in taking into account photochemical enhancement for calculating SCDs of rapidly photolysing species (BrO, NO 2 , and OClO) in zenith-sky geometry. Concerning the zenith-sky simulations, the different models agree generally well, especially below 90 • SZA. At higher SZA, larger discrepancies are obtained with relative differences ranging between 2% and 14% in some cases. In MAX geometry, good agreement is found between the models with the calculated NO 2 and HCHO SCDs differing by no more than 5% in the elevation and solar zenith angle (SZA) ranges investigated (5 • -20 • and 35 • -85 • , respectively). The impacts of aerosol scattering, ground albedo, and relative azimuth on MAX simulations have also been tested. Significant discrepancies appear for the aerosol effect, suggesting differences between models in the treatment of aerosol scattering. A betCorrespondence to: F. Hendrick (franch@oma.be) ter agreement is found in case of the ground albedo and relative azimuth effects. The complete set of initialization data and results have been made publicly available through the QUILT project web site (http://nadir.nilu.no/quilt/), enabling the testing of other RT codes designed for the calculation of SCDs/AMFs.

Airborne DOAS measurements in Arctic: vertical distributions of aerosol extinction coefficient and NO<sub>2</sub> concentration

“…albedo) and the finite vertical resolution of the retrieval. The error from the model itself is neglected, which seems reasonable from previous intercomparison exercises (Hendrick et al, 2006). The two first sources limit the accuracy in relating a profile x to a set of measurements y and correspond to the measurement error in Eq.…”

Chemical ozone loss and ozone mini-hole event during the Arctic winter 2010/2011 as observed by SCIAMACHY and GOME-2

“…In addition, the OClO amount changes rapidly along the path of electromagnetic radiation through the atmosphere and as a function of the solar zenith angle (SZA). These changes can be accounted for by simulations using radiative transfer models (Hendrick et al, 2006;Oetjen et al, 2011, and references therein). However, for the assessment of change, an optimal approach to evaluate changes in OClO measurements is to compare the data at a solar zenith angle of 90 • .…”

Analysis of stratospheric NO<sub>2</sub> trends above Jungfraujoch using ground-based UV-visible, FTIR, and satellite nadir observations

“…The matrix K is determined by consecutively perturbing each layer of the a priori profile and recalculating the set of measurements using the so-called forward model which describes the physics of the measurements. Here, the forward model consists of the stacked photochemical box model PSCBOX coupled to the radiative transfer model (RTM) UVSPEC/DISORT (see Hendrick et al, 2004Hendrick et al, , 2006 for further details about both models). The photochemical model, initialized daily with chemical and meteorological fields from the SLIMCAT 3-D-CTM (Chipperfield et al, 2006), is able to simulate the rapid variation of NO 2 at twilight.…”