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No description available.

The Bi-directional Reflectance Distribution Function (BRDF) is a description of the anisotropic scattering of electro-magnetic radiation by a surface. Mathematical models of the BRDF have the potential to provide estimates of various key environmental variables such as Leaf Area Index (LAI) and Earth surface albedo, by inversion against Earth Observation data. A suite of linear semi-empirical kernel-driven BRDF models, known collectively as AM-BRALS, has been devised by NASA for use with data from the TERRA/MODIS sensor. These have yet to be tested in any comprehensive, operational fashion. This thesis examines the potential of the AMBRALS models (specifically the Ross-Thick Li-Sparse kernel combination), to provide information from directional reflectances acquired by the CNES sensor SPOT-4 VEG-ETATION (VGT). VGT is comparable with MODIS in terms of angular sampling and spatial resolution and thus provides an ideal opportunity to test the AMBRALS suite. Potential weaknesses in the pre-processing of VGT are identified and examined in terms of their impact on the inversion of AMBRALS. These were namely; cloud-masking and atmospheric correction. A new cloud-mask is suggested for VGT data that are to be used with BRDF models. Aerosol optical depth is identified as the atmospheric parameter which has the greatest impact on BRDF model inversion. The information content of VGT acquired directional reflectances and resulting BRDF model products are examined statistically. The complementarity of this information with that already provided by the VGT spectral channels is explored.

This thesis investigates severe local storms in the United Kingdom, specifically tornadoes, waterspouts and severe hailstorms. Reference is also made to the United Kingdom's place in the tornado climatology of Europe and some comparisons are made with the United States. Outline forecast guidance is then considered. A major part of this thesis was the development of computerised tornado, waterspout and severe hailstorm data for the United Kingdom, followed by the validation and verification of as much of the component information as was reasonably possible. A European tornado and waterspout data base was developed likewise. Events that have been reported during the research period have been added to ensure that the data bases are up-to-date. Tornado, waterspout and severe hailstorm climatologies for the United Kingdom are presented. The place of the United Kingdom in the tornado climatology of Europe is discussed and comparisons are made with the tornado climatology of the United States. From the climatologies and several case studies, the possibilities of prediction, detection and warning are considered in outline. It is very much hoped and intended that this research will perpetuate further and more detailed research, as well as development and education. To this end, the thesis concludes with an internet web site on severe weather in general, which has been developed in parallel with this research. The site, of the Tornado and Storm Research Organisation, includes questionnaires developed by the writer which have already proven very useful in attracting numerous new reports of severe weather and also in greater detail than before. The site also serves to increase the awareness of severe weather in the United Kingdom and Europe, as well as to educate visitors about it. The web site in particular lends itself to on-going development.

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No description available.

Understanding the response of glaciers to climate change is critical if estimates of future sea level rise are to be better constrained. A significant portion of recent sea level rise is thought to be from small glaciers, unfortunately these are scattered around the world making their contribution extremely difficult to quantify. Contributions tend to be reported for regions or groupings of glaciers and one of the regions with the largest potential contribution is the Arctic. This region has been identified as being extremely sensitive to climate fluctuations and is expected to be one of the first regions to respond to future climate change. The aim of this research is to quantify the surface change two key glaciers on Svalbard, one of the largest groupings, of glaciers in the Arctic. Surface change will be quantified through the use of Digital Elevation Models (DEMs) derived from aerial images. The quality of the derived surface is dependent on the quality of the ground data used to generate and validate the model. For this reason, extensive field work was conducted to install a network of accurate GPS points around the study glaciers. A Failure Warning Model (FWM) method is used to assess the reliability of the DEMs and the technique is developed through the implementation of a Multiple input Failure Warning Model (MiFWM) method that is more robust. This thesis shows that both study glaciers have experienced significant change during the study period. The calculated rates of change were comparable both to other ground based estimates and other photogrammetric estimates. In addition, the results do not contradict the suggestion that ground based monitoring methods consistently underestimate glaciers contribution to sea level.

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No description available.

The seasonally-varying interaction between the Madden-Julian Oscillation (MJO) and .the northern extratropics, specifically the North Atlantic and Europe region, on intraseasonal timescales is studied. When the MJO is observed using composite and Monte-Carlo significance testing, a direct response to the tropical dynamics is found over the North Atlantic and Europe. When the MJO convection is active over the Indian Ocean, significant anticyclonic anomalies at the 95% confidence level are frequently found over the UK and eastern North Atlantic region. Approximately 10 to 20 days later, when the MJO convection is active over Indonesia, the extratropical anomalies occur in similar locations with opposite sign. Using a systematic two-month sliding season approach to investigate the interaction, the anomalies are present for the majority of the year, favouring the boreal spring. The relationship between the MJO and the North Atlantic Oscillation (NAO) for each of the 12 seasons throughout the year is quantified for the first time using regression analysis. Although correlations between the MJO and NAO are weak, further regressions between the MJO and a North Atlantic 1000 hPa geopotential height index just east of the UK gives very strong boreal springtime correlations of up to r=0.50 and anti-correlations of r=-0.53. An Intermediate Global Circulation Model (IGCM) is used to model the MJO to investigate the mechanisms behind the strong tropical-extratropical interactions. Various stages of representing the MJO in the model are presented using fixed and time dependent heating profiles and many of the observed extratropical features are reproduced as a response to the forcing. Direct comparisons between the observations and the model results are made and the level at which it is able to reproduce the North Atlantic and European anomalies is discussed.