| Summary: | A method is developed and tested for determining atmospheric pressure and tempera-ture from space using spectral absorption by the A and B bands of molecular oxygen as measured by the MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) space instrument in solar occultation mode. MAESTRO is the UV-visible-near-infrared dual grating spectrometer component of the Atmospheric Chemistry Experiment (ACE) scientific payload, and was launched in Au-gust 2003 on the SciSat satellite to investigate atmospheric processes affecting the strato-spheric ozone distribution. On-orbit measurements of pressure and temperature are de-sirable for accurate retrievals of other atmospheric constituents from the instrument, and as independent data products. The constant mixing ratio of molecular oxygen is ex-ploited in these retrievals to derive atmospheric density profiles from oxygen absorption, and the density profiles are then converted to pressure and temperature using hydrostatic balance and the ideal gas law. A highly accurate fast forward model is developed using a fast-line-by-line approach for modelling the high spectral resolution oxygen absorption lines, and a correlated-k technique is used to calculate analytic weighting functions for the retrieval of density. A global fitting algorithm is developed to simultaneously fit all spectra from one occultation. Retrieval characterization shows a small amount of information is added by the inclusion ii of the weaker B band to a retrieval using the strong A band absorption, and tests with real data show the B band retrievals alone are less sensitive to instrument characterization uncertainties and perform better than A band retrievals at altitudes below 30 km. The new algorithm is applied to 230 occultation observations collected in the Arctic winter
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