Abstract
Abstract. Hydroxyl (OH) short-wave infrared emissions arising from OH(4-2, 5-2, 8-5, 9-6) as measured by channel 6 of the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) are used to derive concentrations of OH(v=4, 5, 8, and 9) between 80 and 96 km. Retrieved concentrations are used to simulate OH(5-3, 4-2) integrated radiances at 1.6 µm and OH(9-7, 8-6) at 2.0 µm as measured by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, which are not fully covered by the spectral range of SCIAMACHY measurements. On average, SABER “unfiltered” data are on the order of 40 % at 1.6 µm and 20 % at 2.0 µm larger than the simulations using SCIAMACHY data. “Unfiltered” SABER data are a product, which accounts for the shape, width, and transmission of the instrument's broadband filters, which do not cover the full ro-vibrational bands of the corresponding OH transitions. It is found that the discrepancy between SCIAMACHY and SABER data can be reduced by up to 50 %, if the filtering process is carried out manually using published SABER interference filter characteristics and the latest Einstein coefficients from the HITRAN database. Remaining differences are discussed with regard to model parameter uncertainties and radiometric calibration.
Highlights
Hydroxyl (OH) airglow stems from spontaneous emissions of metastable excited OH molecules which are mainly produced by the exothermic reaction of H and O3 in the upper mesosphere and lower thermosphere (UMLT)
The OH data obtained by SABER have been used by different investigators (Smith et al, 2010; Mlynczak et al, 2013, 2018; Panka et al, 2018) to derive atomic oxygen abundance in the UMLT; deviations of up to 60 % were found in comparison with atomic oxygen data derived from O(1S) green-line measurements obtained by SCIAMACHY and WINDII (Wind Imaging Interferometer) (Kaufmann et al, 2014; Zhu et al, 2015)
We considered OH(3-1) and OH(7-5) emission lines observed by SABER 1.6 and 2.0 μm channels, respectively, and their contributions to the two channels were calculated based on SCIAMACHY OH(3-1) and OH(7-4) measurements
Summary
Hydroxyl (OH) airglow stems from spontaneous emissions of metastable excited OH molecules which are mainly produced by the exothermic reaction of H and O3 in the upper mesosphere and lower thermosphere (UMLT). The OH data obtained by SABER have been used by different investigators (Smith et al, 2010; Mlynczak et al, 2013, 2018; Panka et al, 2018) to derive atomic oxygen abundance in the UMLT; deviations of up to 60 % were found in comparison with atomic oxygen data derived from O(1S) green-line measurements obtained by SCIAMACHY and WINDII (Wind Imaging Interferometer) (Kaufmann et al, 2014; Zhu et al, 2015). While the agreement between new atomic oxygen data obtained by SABER and SCIAMACHY has improved, systematic deviations of up to 50 % still persist (Zhu and Kaufmann, 2018) This systematic difference needs to be addressed in future studies. The obtained radiances were compared to SABER OH radiometric measurements to investigate whether systematic differences exist between the two datasets
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