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Thesis (MSc (Physiology))--University of Stellenbosch, 2000. / 251 leaves single sided printed, preliminary pages and numbered pages 1-151. Includes bibliography, list of appendixes, abbreviations, variables, figures and tables. Digitized at 300 dpi (OCR), using a Bizhub 250 scanner. / ENGLISH ABSTRACT: The Whistle Watch™, an innovative and commercialised peak flow monitor, inspired this study, with its abnormal and complex measuring behaviour. The Whistle Watch™ latter is an audible peak flow monitor with a threshold-activated whistle as the essential component. The whistle is calibrated for a certain flow, and then encased in a body with a variable exhaust valve to atmosphere. Using the Whistle Watch™, with the exhaust valve pre-set, executing a forced expiratory effort, the audible notification of the whistle would indicate a stable asthmatic condition at that setting. No audible notification would result in the use of medication as a preventative measure. Due to the absence of existing theories and literature on the mechanics of whistles, the Whistle Watch™ was empirically developed. This study therefore, focuses on the characterisation and consequent improved understanding ofthe mechanics ofa whistle, with the objective to monitor pulmonary function in a novel way. During this study, a novel technique was developed to determine the reed activation point, or onset of oscillation, in terms of pressure. This technique was then implemented throughout the study. The initial observation and experimentation underlined the whistle's activation sensitivity towards any irregularities of the reed surface. A statistical spread of reed activation pressures defined the reed's inherent non-linear properties. A high dependence of reed activation towards upstream geometry was noted, and a clarification hypothesis was formulated. The effect of reed dimensions on activation pressure was exposed as a complex unexplored field. Existing mathematical reed theories only accommodate steady state oscillations, whereas the completed study indicated a high sensitivity of the reed activation pressure towards different input envelopes. This sensitivity was encapsulated in a mathematical model, with initial support and proofprovided by a previous independent study. All the observed effects and phenomena had far reaching practical application towards the production and quality control ofthe Whistle Watch™. / AFRIKAANSE OPSOMMING: Whistle Watch™, 'n inoverende, kommersieel piekvloeimonitor, was die inspirasie vir die studie, deur sy abnorrnale en ingewikkelde meet-gedragskenrnerke. Laasgenoemde is 'n piekvloeimonitor met 'n fluit wat geaktiveer word by 'n vooraf vasgestelde drempel. Die fluit word gekalibreer vir 'n bepaalde vloei, waarna dit geenkapsuleer word in 'n hoofdeel met 'n veranderlike uitlaat na die atmosfeer. By die gebruik van die Whislte Watch™, met die uitlaatklep gestel op 'n voorafbepaalde vloeitempo, word 'n bepaalde ekspirasievlak verkry. Hierdie vlak het 'n hoorbare kennisgewing tot gevolg, wat 'n stabiele asmatiese toestand aandui. In die afwesigheid van 'n hoorbare respons, word medikasie as voorkornende rnaatreel vereis. Die Whislte Watch™ is empiries ontwikkel in die afwesigheid van bestaande teoriee en literatuur ten opsigte van die werking van fluite. Die fokus van hierdie studie word dus geplaas op die karakterisering van die werking van fluite, wat 'n beter begrip tot gevolg het. 'n Nuwe benadering tot die monitering van die pulrnonere funksie is dus haalbaar. Tydens die studie is 'n unieke tegniek ontwikkel om die aktiveringspunt van die riet, of die aanvang van ossilasie in terrne van druk, te bepaal. Hierdie tegniek is toe dwarsdeur die studie geiinplimenteer. Die fluit se aktiveringssensitiwiteit, in terrne van die oppervlak-onreelmatighede, van die riet was duidelik waarneembaar. Die inherente nie-liniere eienskappe van die riet is duidelik waarneembaar in rietaktiveringsdrukke. 'n Verklarende hipotese is as gevolg van 'n afhanklikheid van die rietaktiveringsdrukke relatief tot stroom-op geometrie, gestel. Die effek wat rietafinetings op aktiveringsdrukke het, was blootgel~ as 'n komplekse onontwikkelde gebied. Bestaande wiskundige rietteoriee maak slegs voosiening vir nie-fluktuerende ossilasies. Na voltooiing van hierdie studie is dit duidelik dat daar wei 'n hoe sensitiwiteit van die rietaktiveringsdrukke bestaan, met verwysing na verskillende ekspiratoriese profiele. Hierdie sensitiwiteit word vervat in 'n wiskundige model met toepaslilke ondersteuning en bewyse uit 'n vorige, onathanklike studie. Aile waarneembare phenomena het resulterende praktiese impakte ten opsigte van die produksie en gehalteversekering van die Whistle Watch™.

Reanalysis products are widely used to study the land-atmosphere exchanges of energy, water, and carbon fluxes, and have been evaluated using in situ data above or below ground. Here measurements for several years at five flux tower sites in the U.S. (with a total of 315,576 hours of data) are used for the coupled evaluation of both below- and above-ground processes from three global reanalysis products and six global land data assimilation products. All products show systematic errors in precipitation, snow depth, and the timing of the melting and onset of snow. Despite the biases in soil moisture, all products show significant correlations with observed daily soil moisture for the periods with unfrozen soil. While errors in 2 meter air temperature are highly correlated with errors in skin temperature for all sites, the correlations between skin and soil temperature errors are weaker, particularly over the sites with seasonal snow. While net shortwave and longwave radiation flux errors have opposite signs across all products, the net radiation and ground heat flux errors are usually smaller in magnitude than turbulent flux errors. On the other hand, the all-product averages usually agree well with the observations on the evaporative fraction, defined as the ratio of latent heat over the sum of latent and sensible heat fluxes. This study identifies the strengths and weaknesses of these widely-used products, and helps understand the connection of their errors in above- versus below-ground quantities.

Atmospheric artifacts superimposed on interferometric synthetic aperture radar (InSAR) measurements have the potential to greatly impede the accurate estimation of deformation signals. The research presented in this dissertation demonstrates a novel InSAR time series algorithm, called HiRAPS algorithm, for effectively estimating high resolution atmospheric phase screens (APS) from differential InSAR measurements. In summary, the HiRAPS algorithm utilizes short time span differential interferograms and rearranges components of existing advanced InSAR techniques to identify a higher density of scatterers used to create the APS. The improved scatterer density allows one to estimate high spatial frequency atmospheric signals not recovered from existing InSAR time series techniques. The HiRAPS algorithm was tested with simulated and actual data, which contain phase contributions from linear and nonlinear deformation, topographic height errors, and atmospheric artifacts. Simulated differential interferograms were generated to have the same spatial and temporal baselines as the actual differential interferograms formed from RADARSAT-1 data over Phoenix, Arizona. The APS superimposed on simulated differential interferograms were then estimated and compared to simulated APS. The root mean square error (RMSE) between the estimated and simulated APS was calculated to qualitatively assess the different values obtained. The RMSE was 0.26 radians when utilizing the HiRAPS algorithm, compared to an RMSE value of 0.39 radians using an implementation of the permanent scatterer (PS) algorithm. The HiRAPS algorithm also showed its applicability for estimating high spatial frequency atmospheric signals for actual data. Sixty-six SAR images, starting from October 5, 2002 and spanning 5 years, were processed for this research. The APS pixel density obtained using the HiRAPS algorithm was 253 pixels per square kilometer, compared to 14 pixels per square kilometer utilizing the PS algorithm. The APS superimposed on the differential interferograms were estimated with both the proposed and PS algorithms. High resolution APS were estimated with the HiRAPS algorithm, whereas only low resolution APS were obtained with the PS algorithm. After estimating and removing estimated APS, the phase stability of APS-free differential interferograms was examined by identifying the permanent scatterers (PS). The final density of identified PS obtained with the HiRAPS algorithm was 453 PS per square kilometer, whereas the density of detected PS using the generic PS algorithm was 381 PS per square kilometer. The maximum difference in the deformation time series between the HiRAPS algorithm and the PS algorithm was less than 6 mm. However, the HiRAPS algorithm resulted in less apparent noise in the time series than the PS algorithm due to the precise estimation of APS. / text

Le radar sondeur Sharad (NASA/ASI) prospecte actuellement la surface et le sous-sol de Mars àune fréquence de 20 ±5 MHz depuis une orbite polaire basse (Mars Reconnaissance Orbiter).L'instrument a pour but de contraindre la composition du sol et de détecter, puis d'interpréter, desinterfaces enfouies afin de restituer le contexte géologique martien à l'échelle régionale. Ce travail dethèse se propose de contribuer à ces objectifs en se focalisant principalement sur l'étude de terrainsglaciaires et péri-glaciaires Martien.Dans un premier temps, par une méthode d'inversion impliquant la reconstruction d'un sousbassementrocheux par interpolation, nous obtenons les paramètres diélectriques représentatifs duvolume de glace d'eau constituant la calotte polaire Nord, Planum Boreum. Nous en déduisons un tauxde pureté du matériel glaciaire > 95 %. Nous fournissons une carte de l'épaisseur des dépôts qui vérifieun volume de glace de 1,14106 km3.Dans une deuxième étude, en confrontant les transects Sharad à des données topographiques etd'imagerie visible, nous élaborons un profil morphologique et stratigraphique complet d'escarpementsglaciaires présents dans la région d'Ultimi Lobe, Planum Australe. Nous appelons ces escarpements"Laps" (large and assymetric polar scarps). La similarité avec des failles listriques associées à desanticlinaux de roll-over nous amène à proposer l'hypothèse de macro-ruptures mécaniques d'une glacesous contrainte extensive et d'un mouvement subséquent par glissement basal.Puis, nous nous intéressons à la réflectivité radar de la surface dont l'amplitude dépend de larugosité et de la permittivité du sol. Nous élaborons une méthode nous permettant de construire unecarte globale de la réflectivité. Afin de séparer les paramètres physiques qui constituent ce signal, nousproposons des méthodes statistiques simples, inspirés du SAR (radar à synthèse d'ouverture) terrestre,complétées par l'élaboration de modèles de rétrodiffusion de surface à incidence normale. Nousmontrons des résultats de cette approche et leur adéquation avec les modèles théoriques. Enfin, nousmettons en évidence une variation temporelle de la réflectivité aux pôles que nous attribuons à laprésence des condensats saisonniers de CO2. Notre méthode d'analyse statistique de la réflectivité,associée à un modèle de rétrodiffusion à trois couches, nous permet d'évaluer la variation d'épaisseurdes condensats dans des régions à très hautes latitudes (80°-85°).

Les modèles météorologiques à aire limitée sont aujourd'hui dotés de systèmes d'analyse de données observées propres, pour la plupart. Ces analyses combinent en général une ébauche provenant du modèle et des observations dans le but de rafraîchir les structures décrites par le modèle à aire limitée. Néanmoins, l'information provenant du modèle coupleur présente également un intérêt. En effet, le modèle coupleur est en général un modèle global bénéficiant de techniques d'assimilation de données performantes, qui permet de fournir une bonne description des grandes échelles notamment. L'objectif de ce travail de thèse est d'injecter l'information issue du modèle coupleur directement dans l'assimilation variationnelle tridimensionnelle (3D-VAR) du modèle à aire limitée, en tant que nouvelle source d'information. Concrètement, on décrit le vecteur d'information entrant dans l'assimilation du modèle à aire limitée comme étant la concaténation des différentes sources d'information : l'ébauche du modèle, les observations et les grandes échelles de l'analyse du modèle coupleur. Ce formalisme utilise une mesure de l'incertitude sur les sources d'information, décrite par les covariances entre les erreurs des différentes sources d'information. Des simplifications sur les covariances croisées entres les sources d'information sont proposées, afin de pouvoir développer le formalisme en vue de le rendre applicable simplement dans un logiciel d'analyse déjà existant. Une première utilisation de ce nouveau formalisme est faite dans un modèle académique unidimensionnel “en eaux peu profondes”, en mettant en oeuvre un modèle coupleur et un modèle couplé. Ces expériences montrent des résultats neutres à positifs, suivant les configurations, limités par le cadre simplifié de ce modèle académique. Dans le cadre de l'application de cette méthode dans les modèles utilisés à Météo- France (modèle global ARPÈGE et modèle à aire limitée ALADIN), une évaluation des statistiques liées aux erreurs sur les sources d'information est menée. Tout d'abord le choix des échelles venant de l'analyse du modèle global est fait, pour ne garder que les plus grandes structures (environ 240 km). Puis les statistiques sont calculées à partir de travaux précédents utilisant des méthodes ensemblistes pour échantillonner les erreurs. L'étude de ces statistiques permet de décrire les propriétés des covariances d'erreurs (écarts types, isotropie, etc.) et de quantifier l'erreur commise en appliquant les simplifications proposées. L'évaluation sur des cycles d'assimilation d'une quinzaine de jours montre que l'introduction des grandes échelles de l'analyse du modèle global a un impact légèrement positif en terme de score objectif. Néanmoins, malgré des différences visibles et systématiques engendrées par l'utilisation de cette nouvelle source d'information, aucun cas d'étude sur des champs diagnostiques, comme les précipitations, ne permet d'illustrer cet apport en terme de temps sensible ou de phénomènes météorologiques spécifiques. Ce travail de thèse propose donc une technique d'analyse en aire limitée permettant de prendre en compte des informations provenant du modèle coupleur, en plus des observations, pour corriger l'ébauche du modèle. Il ouvre la voie à d'autres recherches, notamment en sélectionnant d'autres échelles venant du modèle coupleur à considérer ou en l'étendant par l'ajout de la dimension temporelle.

No description available.

The Atmospheric Chemistry Experiment (ACE) is a satellite mission for remote sensing of the Earth's atmosphere using the solar occultation technique. The primary instrument on this satellite is the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). ACE-FTS retrievals are described with a focus on the creation of <em>a priori</em> temperature and pressure profiles. ACE-FTS measurements are then used to investigate the chemistry, transport and trends of chlorine, fluorine and water in the stratosphere, leading to an improved understanding of processes affecting both stratospheric ozone depletion and global climate change. <br /><br /> Total chlorine (Cl_TOT) in the stratosphere is determined using ACE-FTS measurements of eleven chlorine-containing species, supplemented by both other measurements and models, to determine Cl_TOT as a function of altitude in five latitude zones. All resulting Cl_TOT profiles are nearly linear, with a slight slope. Mean Cl_TOT for 2004 is determined to be 3. 65 ppbv for both the northern and southern midlatitudes (with a precision and estimated accuracy of ??0. 09 and ??0. 13 ppbv, respectively). A slightly lower value of mean Cl_TOT is determined for the tropics and slightly higher values at high latitudes. Total fluorine (F_TOT) in the stratosphere is also determined primarily from ACE-FTS measurements using a similar approach, resulting in stratospheric F_TOT profiles which are nearly linear with mean values ranging from 2. 50 to 2. 59 ppbv for each latitude zone (with a precision of 0. 04-0. 07 ppbv and an estimated accuracy of 0. 15 ppbv). The observed slopes and pattern of latitudinal variation are evidence of the beginning of a decline in global stratospheric chlorine and of the continuing increase in global stratospheric fluorine levels. <br /><br /> The abundance of water in the stratosphere is investigated for the northern hemisphere midlatitudes in 2004 using ACE-FTS measurements. Potential water is determined as [H₂O]+2[CH₄] and from [H₂O] versus [CH₄] correlations, resulting in a value of 7. 14??0. 05 ppmv, which is used to determine a value of 3. 65??0. 15 ppmv for the mean abundance of water entering the stratosphere. Both values are compared directly with historical data from the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument (1985-1994) and show a negligible change, implying that the increases observed by ATMOS and other long-term measurements from that time period have not continued. <br /><br /> The removal of stratospheric water in the Arctic vortex is investigated using ACE-FTS measurements. Using derived quantities from a meteorological data assimilation, northern hemisphere occultations from early 2004 are classified as vortex, vortex edge or extravortex. [CH₄] versus [N₂O] correlations are used to further classify the extravortex occultations as tropical, subtropical or midlatitude. Comparisons between profiles of [N₂O], [CH₄] and [H₂O] inside and outside the Arctic vortex, give estimates of upper stratospheric and lower mesospheric descent rates, indicating that descent in the winter 2004 Arctic vortex was rapid, with evidence of descent at higher altitudes than in past years. <br /><br /> The dehydration of air in the tropical tropopause layer and mechanisms for the entry of water vapor into the stratosphere are investigated by an analysis of ACE-FTS profiles of temperature, water vapor and [HDO]/[H₂O]. Month-to-month comparisons for 2004 and 2005 reveal a clear pattern of seasonal variation and a correlation between minimum temperature and maximum HDO depletion. Further interpretation indicates that the gradual dehydration mechanism accompanied by lofting of ice particles in the tropical troposphere is the most likely explanation for the observed seasonal variation and the shape of the [HDO]/[H₂O] profiles.

The relationships between teleconnection patterns the Pacific/North American (PNA) index, North Atlantic Oscillation (NAO) and the El Nino/Southern Oscillation (ENSO)—and lake-effect snowfall are examined. Bivariate and partial correlations are used over seasonal and semi-seasonal periods for stations within the Lake Erie snowbelt to link teleconnection phases to snowfall increases. Significant negative correlations were seen throughout the entire winter between NAO and snowfall. Relationships between PNA and ENSO on snowfall were less evident, with significant correlations during the mid-winter months between a positive PNA and snowfall and significant correlations during the late winter in the western zone between a negative ENSO and snowfall. / Department of Geography

Since an extratropical transition (ET) of a decaying tropical cyclone (TC) often results in a fast-moving, rapidly developing extratropical cyclone and amplification of synoptic-scale systems far downstream, proper forecasting of ET events is critical to forecast accuracy over large ocean regions. Past studies have linked forecast accuracy to the phasing of a decaying TC with favorable midlatitudes conditions. Because ET events are sensitive to the analyzed initial conditions, this phasing is examined using 11 member ensemble predictions available four times daily from the National Centers for Environmental Prediction, which were combined into a single 44 member ensemble based on a common forecast verification time. Recurring ET patterns within the 44 member ensemble were objectively identified using a combination of EOF and cluster analysis. Ensemble spread first appears near the point where the TC moves into the midlatitudes and then propagates downstream. Although ensemble spread in the forecast fields was large at extended forecast intervals, the ensemble spread, and the number of ET patterns identified in successive EPS predictions, decreased as the ET process became better defined. Within 48 hours of the ET event, the ensemble prediction system properly identified the ET pattern with a minimum ensemble spread. Similar to Klein et al. (2002), the shifts in the initial position of the TC and the subsequent dynamical coupling can explain differences between weak and strong ET reintensifications.