This thesis consists of analysis of three different data sets: (i) Aircraft-based eddy correlation data collected above irrigated and non-irrigated agricultural land in Southern California during the California Ozone Deposition Experiment (CODE) summer 1991; (ii) micrometeorological tower data, collected over grape and cotton canopies as part of CODE; (iii) aircraft-based eddy correlation flux data above two grid sites in the Canadian boreal forest during the Boreal Ecosystem-Atmosphere Study (BOREAS), spring and summer of 1994 and 1996. / Results from the CODE aircraft data document composition and size of the dominant structures, which transport heat and gases (H2O, CO 2 and ozone) over water stressed and non-water stressed surfaces, and the relative frequency with which structures carrying only a single scalar, or given combinations of scalars, were encountered along the flight paths. Interpretation of results provides further evidence for the existence of a second (nonphysiological) sink for ozone. The relative preponderance of structures that carry moisture, carbon dioxide and ozone simultaneously, particularly in the gradient-up mode, reflects the importance of vegetation as co-located source/sink for these scalars. The detrending procedures described in this study may help to define a more effective separation between local and mesoscale events in biosphere-atmosphere interaction. / Results from the CODE tower data indicates a single vegetated ozone sink for the grape site, but a vegetated as well as a non-vegetated sink for the cotton site. For both sites, structures simultaneously transporting significant flux contributions of CO2, H2O, heat and ozone dominate during unstable conditions. During stable conditions, unmixed single flux structures dominated over cotton but not over grape. The results of this study contribute empirical evidence about the relationship between ozone uptake and the physical and physiological state of vegetation, as well as the limitations placed on eddy scales in simulation models. / Results from the BOREAS aircraft data shows a decoupling between the surface and the atmosphere, where the patterns of vegetation, greenness and surface temperature may be quite dissimilar to those of the fluxes of sensible heat, latent heat and---to a lesser degree---CO2. Reasons for this lie in the extraordinary boundary layer conditions, high vapour pressure deficit, moist soil and hot canopies, and the response of the vegetation to these conditions. Analysis of the coherent structure compositions to some extent permits the characterization of the different sources and sinks. Overall, this study shows the importance of understanding the various interacting components of soil, vegetation and atmosphere when attempting to design process-based models for predictions in 'micrometeorologiacally' complex ecosystems.

The aim of this thesis is to examine the nature and characteristics of tropospheric ozone over Johannesburg, South Africa. Ozone, water vapour and meteorological profile data, which form part of the MOZAIC (Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft) database for the period 1995 to 2000 were utilized in this study. The thesis is divided into two main parts. The first part deals with the computation of total tropospheric ozone. A clear seasonal cycle, with ozone peaking in September and October is found. It is suggested that the main reason for the spring maximum is biomass burning, combined with prevailing anticyclonic circulation patterns, which facilitate the build-up of ozone over the region. Variability in TTO is greatest in January, September and November and least during autumn and winter (April to July). The lower day-to-day variability in autumn and winter is a reflection of the more settled weather at this time. Interannual variability is least in January and April to June. The autumn and winter ozone values are more consistent and appear to represent background tropospheric ozone loadings on which the dynamic and photochemical influences of other months are superimposed. High TTO events (>30 DU) occurred predominantly during September and October. Enhancements in the lower troposphere occurred mostly in September and seldom lasted for more than 1-2 consecutive days. It is suggested that these events are most likely due to effects of local surface pollution sources, either localised biomass burning or urban-industrial effects. An extended period of enhancement in the 7-12 km layer occurred from 14-17 September 1998 and again on 20 September 1998. The extended duration of this event suggests that it is due to an STE event. Confirmation of this was given in a case study of a particular MOZAIC flight on 16 September 1998 from Johannesburg to Cape Town. The second part of the thesis deals with the classification of ozone profiles and is used to find pattern and order within the profiles. TWINSPAN (Two-Way INdicator SPecies ANalysis), a cluster analysis technique, was used to classify the profiles according to the magnitude and altitude of ozone concentration. Six distinct groups of profiles have been identified and their characteristics described. The HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) trajectory model was used to relate the profiles to the origin of air masses, revealing clearly defined source regions. The mid-tropospheric peak in summer and the low to mid-tropospheric enhancement in spring is attributed to continental areas over central Africa and long-range transport while local sources are responsible for the winter low tropospheric enhancement. Reduced ozone values are due to westerlies bringing in clean maritime air. The classification has highlighted three important findings. Firstly, it has emphasized the pronounced seasonality of ozone profiles. It is evident that seasons are dominated by particular patterns and by inference, the processes and transport patterns that shape individual profiles are seasonally dependent. Secondly, the widely recognized spring maximum in tropospheric ozone has been confirmed in this classification, but a new and equally high summer mid-tropospheric enhancement due to the penetration of tropical air masses from continental regions in central Africa has been identified. Thirdly, it is suggested that the computation of a mean profile and furthermore, extrapolation of trends based on a mean profile is meaningless, particularly for a location on the boundaries of zonally defined meteorological regimes. / Thesis (M.A.)-University of Natal, Durban, 2002.

No description available.

Propulsé sur une orbite polaire en avril 1995 par l’Agence Spatiale Européenne, l’instrument Global Ozone Monitoring Experiment (GOME) est le précurseur d’une nouvelle génération de satellites dédiés à la mesure globale de la composition atmosphérique. Ce spectromètre hyperspectral mesure, entre 240 et 790 nm, à la résolution de 0,2-0,4 nm, la radiance diffusée par l’atmosphère et réfléchie par la surface terrestre et les nuages au nadir du satellite. La technique de spectroscopie d’absorption optique différentielle (DOAS) permet d’en inverser la concentration columnaire de l’ozone et du dioxyde d’azote atmosphériques.<p><p>Les travaux décrits dans cette thèse portent d’une part sur la caractérisation du contenu en information géophysique accessible par ce type de sondage atmosphérique, et d’autre part sur la mise au point des méthodes et algorithmes d’inversion propres à la mission GOME. <p><p>Au cours des premiers chapitres, nous établissons les propriétés pluridimensionnelles de lissage et d’échantillonnage du champ atmosphérique associées à l’observation du rayonnement diffusé. Nous explorons ensuite les problèmes posés par le cycle diurne des oxydes d’azote, ainsi que l’effet des gradients atmosphériques interférant avec le chemin optique. Nous analysons enfin les capacités des réseaux de télédétection de l’Organisation Mondiale Météorologique (OMM) pour le diagnostic des algorithmes et données des systèmes satellitaires.<p><p>Deux chapitres sont ensuite consacrés à la mise au point des méthodes et algorithmes d’inversion DOAS pour le processeur GDP, qui traite de manière opérationnelle les données radiométriques acquises par GOME. Nous abordons successivement le problème de la dépendance en température des sections efficaces d’absorption, l’évaluation du facteur d’amplification géométrique du chemin optique, l’estimation de la colonne fantôme masquée par les nuages, les effets de l’anomalie magnétique sud-atlantique des ceintures de radiation, et l’incidence du dioxyde d’azote troposphérique. Suit un diagnostic systématique de la mise au point du processeur GDP sur base des données globales fournies par les réseaux de l’OMM, ainsi qu’une critique comparée des algorithmes TOMS de la NASA.<p><p>Le dernier chapitre décrit la construction de la première climatologie globale du dioxyde d’azote stratosphérique et de ses variations harmoniques. Développée pour nos études du facteur d’amplification géométrique, cette climatologie composite est issue de l’analyse conjointe des jeux de données complémentaires acquis par différents satellites, par des réseaux au sol et par des ballons stratosphériques.<p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished