Improved Temperature and Pressure Profiles Retrieved from the ACE-Maestro Spectra Based on Revised O2 a- and b- Bands Spectral Parameters

Abstract:

The MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) is a UV-Visible-NIR low-resolution spectrometer on-board the Canadian satellite SCISAT as part of the Atmospheric Chemistry Experiment (ACE) mission flying along with a Fourier Transform Spectrometer (the ACE-FTS) since 2003. It collects solar occultation spectra in the visible and near infrared regions of the solar spectrum from 400-1010 nm with resolution of approximately 2 nm. MAESTRO is able to measure strong absorption features of the oxygen molecule in A- and B-bands at 762 nm and 690 nm, respectively, which are used to derive atmospheric temperature and pressure profiles. The retrieval algorithm is based on a global fit that simultaneously fits all spectra from a single occultation to determine a density profile, which is then used to determine pressure and temperature. The forward model uses a fast line-by-line calculation and correlated-k technique to accurately model atmospheric absorption and the nonlinear saturation effects in the occultation geometry. The O₂ spectroscopic parameters formerly used in forward model were from HITRAN (high-resolution transmission molecular absorption database) 2004. O₂ A- and B-band spectral features have been significantly improved in the most recent update of HITRAN (2012). This paper discusses the improvement of the retrievals and retrieval uncertainties with the new oxygen parameters. Temperature-pressure profiles derived using these new parameters are compared with previous profiles, the profiles retrieved from ACE_FTS (Fourier Transform Spectrometer) data, and coincident radiosonde measurements.