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Title: Characterisation and error analysis of H2O retrievals from the UARS microwave limb sounder experiment
Author: Suttie, Martin R.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1995
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The Upper Atmosphere Research Satellite (UARS) was launched on 12th September 1991 carrying a payload to measure the chemistry, dynamics and energy balance of the middle atmosphere. The Microwave Limb Sounder (MLS) onboard UARS makes measurements of atmospheric thermal emission at millimetre wavelengths which are used to infer molecular abundances throughout the stratosphere and mesosphere. Measurements made at 183.3 GHz are used to retrieve concentrations of water vapour (H2O). Measurements of water vapour on a global scale are of particular importance to the study of stratospheric photochemistry, radiation budget and dynamics. MLS provides approximately 19 months of near continuous water vapour measurements on a global scale. A characterisation and error analysis, based on the formalism of Rodgers, [1990], is performed for the UARS MLS 183 GHz H2O retrievals. The useful vertical range for scientific studies with MLS Version 3 H2O retrievals is found to be 22-0.2 hPa at high latitudes and 46-0.2 hPa elsewhere. For this vertical range, the estimated vertical resolution of the retrievals is 5-6 km. In the error analysis, estimates of the contributions of both random errors, including the smoothing error, and systematic uncertainties to the overall error in retrieved H2O are produced. It is found that the retrievals at 46 hPa and 22 hPa contain an increased contribution from the a priori information at high latitudes during the polar winter which is due to a corresponding loss of information from the radiance measurements. This is linked to the use of an opacity criterion which does not permit radiance measurements which arise from optically thick limb paths to be included in the retrieval. A new opacity criterion is developed in an attempt to improve the retrieval at 46 hPa and 22 hPa. Test retrievals show that it is possible to reduce the contribution from the a priori information to an acceptable level, but at 22 hPa a systematic increase in the H2O mixing ratio occurs which requires further investigation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available