Abstract
Abstract. The Optical Spectrograph and InfraRed Imaging System (OSIRIS) on the Odin satellite is currently in its 12th year of observing the Earth's limb. For the first time, continuous temperature profiles extending from the stratopause to the upper mesosphere have been derived from OSIRIS measurements of Rayleigh-scattered sunlight. Through most of the mesosphere, OSIRIS temperatures are in good agreement with coincident temperature profiles derived from other satellite and ground-based measurements. In the altitude region of 55–80 km, OSIRIS temperatures are typically within 4–5 K of those from the SABER, ACE-FTS, and SOFIE instruments on the TIMED, SciSat-I, and AIM satellites, respectively. The mean differences between individual OSIRIS profiles and those of the other satellite instruments are typically within the combined uncertainties and previously reported biases. OSIRIS temperatures are typically within 2 K of those from the University of Western Ontario's Purple Crow Lidar in the altitude region of 52–79 km, where the mean differences are within combined uncertainties. Near 84 km, OSIRIS temperatures exhibit a cold bias of 10–15 K, which is due to a cold bias in OSIRIS O2 A-band temperatures at 85 km, the upper boundary of the Rayleigh-scatter derived temperatures; and near 48 km OSIRIS temperatures exhibit a cold bias of 5–15 K, which is likely due to multiple-scatter effects that are not taken into account in the retrieval.
Highlights
Unlike in the lower atmosphere, where increases in CO2 give rise to a heating effect, in the middle atmosphere, due to CO2 relaxation through spontaneous emission into space, an increase in CO2 leads to a cooling effect (e.g., Berger and Dameris, 1993; Schmidt et al, 2006)
In order to assess the validity of the Optical Spectrograph and InfraRed Imaging System (OSIRIS) mesospheric temperatures, the new OSIRIS research product is compared with coincident temperature profiles from the satellite-based instruments Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS), and Solar Occultation For Ice Experiment (SOFIE), as well as the ground-based Purple Crow Lidar (PCL), located near London, Ontario, Canada
All OSIRIS subsets and instrument datasets were filtered for outliers prior to comparing temperature profiles
Summary
Unlike in the lower atmosphere, where increases in CO2 give rise to a heating effect, in the middle atmosphere, due to CO2 relaxation through spontaneous emission into space, an increase in CO2 leads to a cooling effect (e.g., Berger and Dameris, 1993; Schmidt et al, 2006). Retrievals at higher wavelengths, e.g. λ > 650 nm, where there is much less O3 or NO2 absorption are not possible, since at these higher wavelengths there is significant contamination in the observed signal due to aerosol scattering At this time, retrievals are limited to tangent height observations above 45 km, rather than incorporating simultaneous OSIRIS measurements of O3, NO2, or aerosol profiles into the retrieval. Rayleigh-scattering cross-sections are calculated at each pixel wavelength according to the method detailed by Bucholtz (1995), and [M] profiles from the NRLMSISE-00 model (Picone et al, 2002) corresponding to the OSIRIS observations are used as a priori profiles In both wavelength regimes, the forward model assumes a constant solar flux, determined from the mean of 2003–2009 daily average spectral irradiance values from the Spectral Irradiance Monitor (SIM) instrument (Harder et al, 2005) on the Solar Radiation and Climate Experiment (SORCE) satellite (Sparn et al, 2005). The OSIRIS temperature dataset has not yet been made publically available on the OSIRIS website, it can be obtained through personal communication with the corresponding author
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