Retrieval of high-altitude temperature profiles from atmospheric limb-scattered radiance

Details

Supervisors

Dekemper, Emmanuel

Faculty

Faculté des sciences

Degree label

Master [120] en sciences physiques, à finalité approfondie

Abstract

While the Earth’s surface and the lower part of the atmosphere, the troposphere, are becoming warmer due to the increase in greenhouse gas concentrations, recent observations indicate that the middle atmosphere, the stratosphere and the mesosphere, are cooling. Paradoxically, this cooling is also caused by the increase in long-lived greenhouse gases: they broadly reradiate their energy which, from the higher atmosphere, can escape to outer space. Monitoring the cooling of the upper atmosphere is another important component of the global efforts to track the anthropogenic climate change. In this Master’s thesis, a radiative transfer model (RTM) is developed to describe the propagation of solar radiation in a spherical-shell atmosphere, assuming that photons are scattered only once before reaching the detector (single-scattering approximation). This approximation is justified by the low air number density in the middle atmosphere compared to the troposphere, which makes multiple scattering negligible over the altitude range considered (approximately 35–80 km). The model is implemented in Python and validated against the reference RTM SASKTRAN. The validated model is then used to process the Ozone Mapper and Profiler Suite Limb Profiler (OMPS-LP) observations, considering Rayleigh scattering as the sole scattering process and accounting only for extinction by Rayleigh scattering and ozone absorption. Atmospheric number density profiles are retrieved using a standard inverse retrieval scheme, from which temperature profiles are derived using the combination of the hydrostatic equilibrium equation and the ideal gas law.