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The focus of this thesis is the tracking of apparent motion from sequences of meteorological satellite images, in the context of Atmospheric Motion Vector (AMV) derivation. AMVs are estimates of atmospheric wind, they are routinely produced from visible, infrared window and water vapour (WV) imagery, and they represent a major contribution to the observation of the Earth's atmosphere. This research tackles a number of issues related to the derivation of AMVs from WV imagery, using region-matching methods for tracking motion. WV imagery is particularly challenging, as images typically have a soft appearance, with no edges, no background, and large areas of low contrast. The datasets used in the experiments are real sequences of images in the WV 6.2 urn band from the geostationary satellite Meteosat-9. The underlying approach throughout the thesis is Gaussian multi-scale representation, a sound mathematical framework, developed by the computer vision community, that allows to analyse images at differente scales and to handle partial derivatives in a way deeply connected to the scale. The main contributions of this thesis are: It shows how Gaussian multi-scale representation can be used with WV meteorological satellite imagery, and in particular its value to handle scales and spatial derivatives. It proposes a new method to detect locations of interest, based on a difference of Gaussians, and shows that it performs better than other detectors, including those commonly used in operational AMV derivation schemes, in the experiments carried out with Meteosat-9 imagery. It proposes a group of distances, based on the Sobolev norm HI, which includes a term to evaluate partial derivatives, to quantify the similarity between neighbourhoods, and it shows that these distances produce better results than the widely used £2 norm, especially when the weight given to the derivatives term is relatively large.

i~to a stratosphere-troposphere version of the Met Office assimilation system, producing one of the first analyses to reproduce the September 2002 split of the Antarctic polar vortex. The aim of the project was to investigate the benefit of assimilating MIPAS retrievals and to assess the Met Office 3D-Var assimilation system by examining its different components. The ozone analysis was found to agree with independent ozone observations through most of the middle and upper stratosphere, biases above 60 hPa being within the range -20% to +10% and typically smaller. More significant positive biases were found in the lower stratosphere and inside the polar vortex. Although ozone amounts are shown to be slightly overestimated by MIPAS retrievals in these same regions, these biases are demonstrated to be caused by shortcomings in the model chemistry and transport. MIPAS data have been shown to have a limited impact on the Met Office temperature analysis, although a ' positive effect was identified at the mesopause. It is shown that MIPAScould bring larger benefits if more realistic background error statistics were used for ozone, especially in the lower stratosphere. Based on an evaluation of these statistics using independent datasets, it is suggested that background error variances should be decreased near the ozone maximum and increased below 70 hPa It is also recommended to introduce latitudedependence in vertical error correlations and height-dependence in horizontal error correlations. Improvements are also proposed to improve the ozone assimilation in the polar vortex region. Finally, analysed winds have been found to induce errOneous transport of ozone by increasing vertical diffusion of ozone and enhancing the mean zonal circulations. This especially affects the tropics, where ozone analyses reveal excessive exchanges of air parcels between the stratosphere and the troposphere.

This thesis presents new estimates of the components of the longwave radiation (LW) part of the Earth's global annual mean energy budget. The study is motivated by a schematic diagram of the Earth's Energy Budget widely used by the sci.entific community since its publication in the late 1990's. Nevertheless, estimates presented in this diagram were produced using a single standard temperatur e and gaseous vertical profile to represent the whole global atmosphere and a radiative code that can no longer be considered state-of-the-art. This thesis evaluates the reference diagram by calculating the geographical distribution ofLW components using an 12-year climatological dataset and outputs from a state-of-the-art line-by-line radiation code as input to a discrete ordinate scattering model. The direct radiative effect of mineral dust aerosol and the scat- . tering impact by cloud particles on the LW radiation budget are also studied. The global annual mean Outgoing Longwave Radiation (OLR), downward irradiance at the surface for cloudy sky and cloud LW forcing are found to be 235,341 and 27 Wm-2, respectively and are in good agreement with satellite and surface observations. Comparison between the present and reference diagram estimates shows differences up to 20 Wm-2 for some coqiponents. Natural and anthropogenic mineral dust aerosols globally reduce OLR by around 0.20 Wm-2 and regionall~ reduce OLR up to 10 Wm-2 under high dust concentration conditiolilS. The effect of multiple scattering by clouds particles on LW is found to decrease OLR by 3 Wm-2 with a hitherto unrecognised contribution from low clouds. AJthough this effect of 3 Wm-2 appears small compared to the global mean OLR value of 235 Wm-2 , neglecting scattering will lead to 10%biases in the global mean LW cloud forcing. Given the current observational and computational knowledge of radiative transfer, this thesis provides one of the most elaborate estimates of LW irradiances, which are an update of the reference diagram of the Earth's energy budget.

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