Dissertations / Theses on the topic 'Atmospheric circulation Pacific area'

Thesis (Ph. D.)--Woods Hole Oceanographic Institution and Massachusetts Institute of Technology, 1990.
Funding was provided by the Office of Naval Research and a Secretary of the Navy Graduate Fellowship in Oceanography. References : p. 117-121.

Thesis (Ph. D.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2006.
Dickinson, Robert, Committee Member ; Black, Robert, Committee Chair ; Cunnold, Derek, Committee Member ; Fu, Rong, Committee Member ; Knox, John, Committee Member.

Intense atmospheric convection associated with the South Pacific Convergence Zone (SPCZ) significantly impacts basin-scale circulation patterns over the Pacific. We explore dynamical processes which foster changes in convection along the convergence zone. These forcings include strong moisture convergence and accumulation of wave energy in the boundary layer, as well as dynamical instability associated with moderate cross-equatorial wind bursts. A focus is applied to observing the dominant modes of variability on synoptic to intraseasonal timescales using a combination of satellite observations and NCEP reanalysis data. Accumulation of energy, due to negative stretching deformation, occurs with both tropical and extratropical modes suggesting that the SPCZ is an artifact of wide ranging modes. Signals of the dominant modes (inferred from fields of outgoing longwave radiation: OLR) are isolated using bandpass filtering techniques, which are then mapped in space and time using Principal Components from Empirical Orthogonal Function analyses. Variability of convective systems in the SPCZ is found to be significantly correlated with changes in the regional Hadley Circulation and the Pacific Walker cell. This co-variability presents the possibility of important teleconnection routes between the tropical West and East Pacific, as well as with the mid-latitude regions of the Northern and Southern Hemispheres. We test these interaction hypotheses by developing composites of the circulation patterns using dates of maximum convection events (regions of minimum OLR) in the SPCZ. Intensities of the large-scale circulations are measured using observations of stream function mass fluxes. Results suggest that deep convection maxima (minima) are associated with an increase (decrease) in the Walker Circulation. It is also illustrated how off-equatorial convection anomalies in the subtropical portion of the SPCZ may induce changes to the Hadley Circulation. Interactions with the zonal (Walker) and meridional (Hadley) circulations appear to have important consequences on the ability for wave energy to propagate through the tropical Pacific atmosphere. Examples include Northern Hemisphere cross-equatorial teleconnections through the Westerly Wind Duct in the upper branch of the Walker circulation and Rossby wave trains in the SPCZ, which may be partially governed by characteristics of the regional Hadley circulation.

Widespread droughts can have considerable impact on western United States (U.S.) streamflow but causes related to moisture delivery processes are not yet fully understood. Here we examine western U.S. streamflow records to identify robust leading modes of interannual variability and their links to patterns of ocean and atmospheric circulation. The leading mode of streamflow variability, a pattern of west-wide streamflow anomalies, accounts for approximately 50% of variability and is associated with persistent high-pressure anomalies related to ridges off the Pacific North American coast. The second mode of variability accounts for approximately 25% of variability and is associated with ocean and atmospheric conditions in the tropical Pacific. Our results suggest that the leading mode of streamflow variability in the western U.S. is more strongly associated with internally driven midlatitude atmospheric variability than equatorial Pacific sea surface temperatures.

The remarkable salinity difference between the upper Pacific and Atlantic Oceans is often explained through net export of water vapour across Central America. To investigate this mechanism a study of salinity signals in the Equatorial Pacific Ocean current system was made looking at responses to fresh water input from two sources (local versus remote - Atlantic Ocean) as well as a combination of the two. Statistical analyses (Empirical Orthogonal Functions, Single Value Decomposition and Wavelet analysis) were used to split the main sources of the atmospheric freshwater input into local and remote contributions and to quantify both contributions. The remote source was assumed to have been transported over Central America from the Atlantic Ocean as an atmospheric freshwater flux, whereas the local source originated in the Pacific Ocean itself. The analysis suggests that 74% of the total variance in precipitation over the tropical eastern Pacific is due to water vapour transport from the Atlantic. It also demonstrates strong influence of ENSO events, with maximum correlation at a two months time lag. During La Ni�a periods the precipitation variance is more closely related to water vapour transport across Central America (the remote source), while during El Ni�o periods it is more closely related to the water vapour transport by Southerly winds along the west coast of South America (the local source). The current and temperature fields provided by the Modular Ocean Model (version 2) were used to study the changes in the salinity field when freshwater was added to or removed from the model. ECMWF ERA-40 data taken from the ECMWF data server was used to determine the atmospheric flux of freshwater at the ocean surface, in the form of evaporation minus precipitation (E-P). The Mixed Layer Depth (MLD) computed from temperature and salinity fields determines to what depth the salinity's dilution/concentration takes place for every grid point. Each MLD was calculated from the results of the previous time step, and the water column was considered well mixed from the surface to this depth. The statistical relationships were used to reconstruct the precipitation over the tropical eastern Pacific. A numerical ocean model, which uses currents and temperature from a global ocean model and is forced by precipitation, was used to study the ocean's response to either the remote or the local source acting in isolation. Through time lag correlation analysis of the sea surface salinity anomalies produced by the variation in the reconstructed precipitation fields, it is found that the anomaly signals of salinity propagate westward along the Equator at a rate of approximately 0.25 m.s-1 (6.1 degrees per month).

Thesis (M. S.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2009.
Committee Chair: Kim Cobb; Committee Member: Annalisa Bracco; Committee Member: Ellery Ingall; Committee Member: Jean Lynch-Stieglitz; Committee Member: Yuhang Wang.

Thesis (Ph. D.)--University of California, San Diego, 2006.
Title from first page of PDF file (viewed December 12, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 126-133).

Tropical and extratropical Pacific decadal climate variability substantially impact physical and biological systems in the Pacific Ocean and strongly influence global climate through teleconnection patterns. Current understanding of Pacific decadal climate variability centers around the El Niño-Southern Oscillation (ENSO), the Aleutian Low (AL), and the Pacific Decadal Oscillation (PDO). However, recent literature has highlighted the emerging roles of secondary modes of variability of the tropical and extratropical Pacific atmosphere and ocean in global climate change: the Central Pacific Warming (CPW) phenomenon, the North Pacific Oscillation (NPO), and the North Pacific Gyre Oscillation (NPGO). This work analyzes the statistics and uncertainties behind Pacific interannual and decadal-scale climate variability, and focuses on better understanding the roles of the CPW, NPO, and NPGO in the climate system. The study begins by examining the dynamics of the NPO and its role in Pacific interannual and decadal climate variability. Results illustrate that the individual poles of the NPO have relations at high frequencies, but only the southern node contains a deterministic low-frequency component, which is forced by tropical Pacific sea surface temperature (SST) variability, as shown with a modeling experiment. The NPO-induced variability by the tropical Pacific SST is then integrated by the underlying ocean surface to form the decadal-scale NPGO signal. Thus, a new link between the CPW, the NPO, and the NPGO is formed, expanding the current framework of Pacific decadal variability and its implications for weather and climate. The new framework of North Pacific decadal variability (NPDV) is then evaluated in 24 state-of-the-art coupled climate models. Results indicate that the models in general have difficulty reproducing the leading modes of NPDV in space and time, particularly the NPGO mode and its connection to the NPO. Furthermore, most models lack the proper connections between extratropical and tropical Pacific, for both the ENSO/AL/PDO and CPW/NPO/NPGO connections. Improvements in these teleconnections are thus needed to increase confidence in future climate projections. The last part of the dissertation explores further the importance of the CPW mode by comparing and contrasting two popular paleoclimate SST anomaly reconstruction methods used for tropical Indo-Pacific SSTs. The first method exploits the high correlation between the canonical ENSO mode and tropical precipitation; the second method uses a multi-regression model that exploits the multiple modes of covariability between tropical precipitation and SSTs, including the CPW mode. The multi-regression approach demonstrates higher skill throughout the tropical Indo-Pacific than the first approach, illustrating the importance of including the CPW phenomenon in understanding past climates.

This thesis concerns two topics: the kinematics of Pacific cross-equatorial flow ??? the location, timing and magnitude of the flow; and their dynamics???what are the driving forces controlling the flow? Despite extensive observations in the central and eastern Pacific, observations of these flows remain contradictory. We use output from an Ocean General Circulation Model (OGCM) viewed from a Lagrangian framework on density layers. This addresses the problem of high variability due to features such as Tropical Instability Waves. The annual mean flow is found to be southward nearly everywhere, east of 140??W. Flow becomes stronger in the second half of the year due to a bolus transport of very light surface water, introduced by Tropical Instability Waves. A Tropical Cell pattern occurs along the equator that does not require diapycnal downwelling. From 160??E to 160??W the annual mean flow is northward, occurring mostly in the mixed layer, appearing to originate partly from the Equatorial Undercurrent surfacing in the east. The northward flow is strongest in March and becomes southward in September. The wind stress and nonlinear terms are shown to be the key driving features, with a prescribed biharmonic Smagorinsky horizontal friction scheme having negligible impact. From 160??E to 160??W, the flow is partly accounted for by an Ekman forcing, with the curl of the nonlinear term providing a crucial additional torque, more than doubling the magnitude in some instances. From 160??W to 120??W the wind stress curl provides a weak southward flow of about 1 Sv, which increases by the nonlinear addition to around 5 Sv. The curl of the steady component of the nonlinear term, derived from annual mean currents, is similar in structure to the total nonlinear term, but higher in magnitude. The structure of the variable term, which was mostly of opposite sign to the steady term, suggests damping occurs in place of friction. While our study is limited to an examination of the model's characteristics, our results provide important clues to the observed flow patterns not resolved by present-day measurements. This study also highlights the importance of time-space variability and both horizontal and vertical density structure in controlling the flow and its feedback on the system.

Three semi-permanent cloud bands exist in the Southern Hemisphere extending southeastward from the equator, through the tropics, and into the subtropics. The most prominent of these features occurs in the South Pacific and is referred to as the South Pacific Convergence Zone (SPCZ). Similar convergence zones, with less intensity, exist in the South Atlantic (SACZ) and Indian (SICZ) oceans. We attempt to explain the physical mechanisms that promote the diagonal orientation of the SPCZ and the processes that determine the timescales of its variability. It is argued that the slowly varying sea surface temperature patterns produce upper tropospheric wind fields that vary substantially in longitude. Regions where 200 hPa zonal winds decrease with longitude (i.e., negative zonal stretching deformation, or dU/dx<0) reduce the group speed of the eastward propagating synoptic (3-6 day period) Rossby waves and locally increase the wave energy density. Such a region of wave accumulation occurs in the vicinity of the SPCZ, thus providing a physical basis for the diagonal orientation and earlier observations that the zone acts as a "graveyard" of propagating synoptic disturbances. In essence, dU/dx=0 demarks the boundary of the graveyard while regions where dU/dx<0 denote the graveyard itself. Composites of the life cycles of synoptic waves confirm this hypothesis. From the graveyard hypothesis comes a more general theory accounting for the SPCZ's spatial orientation and its longer term variability influenced by the El Niño-Southern Oscillation (ENSO), or alternatively, the changing background SST associated with different phases of ENSO.

The investigation of climate variability in different timescales such as daily, monthly, seasonal and inter-annual has utmost importance for managing the socio-economic processes on regional to global scale. Indeed, the variation in the climate has a crucial impact on agriculture, water, health, tourism, economy and transportation. Therefore the development of climate forecasting tools is necessary which helps to manage these sectors more efficiently. However, there are limitations on producing accurate climate forecast for more than two weeks in advance due to the chaotic nature of the climate system, especially for the region like the Mediterranean, which is characterized by high interannual variability. Due to its importance and challenging nature, a collective effort is being done to improve the skill of models and climate forecasting in the Mediterranean. The contribution of this thesis is a overall effort, which consists of developing a high resolution model application in the Mediterranean, which can provide reliable estimate of Sea Surface Temperature (SST) and Mixed Layer Depth (MLD). This approach is based on the fact that the atmospheric predictability in seasonal to interannual time scale is significantly dependent on slowly varying lower boundary conditions (e.g. Charney and Shukla 1981) i.e. Mediterranean SSTs. The spatial resolution of model is increased for taking into account the mesoscale processes in the Mediterranean. Since the first internal Rossby radius of deformation in the Mediterranean sea is of the order of 10-15 kms, the spatial resolution of an eddy resolving model should have at least a resolution one half of the Rossby radius. Based on this assumption, the spatial resolution is explored to the order of -5 km (1/16°). The regional ocean modeling system (ROMS) adopted from the Rutgers University is used in the current study. The objective is to validate certain fields (such as SST and MLD) obtained from model simulations and study air-sea interactions. The validation is done by performing two experiments namely, climatological and interannual simulations. The model simulated results are validated with observations as well as intercompared to evaluate the skill of model. The monthly mean SST climatology is obtained from ten years of model run forced with climatological air-sea fluxes is well captured by the model configuration and follows the annual cycle. Model simulated summer SST climatology shows biases of the order of 0.8-1.0 °C with observation (MedAtlas) and 1.0-1.2 °C with other datasets (intercomparison). The vertical structure of temperature climatology is found to be well simulated by model in which upper layer shows a difference of 1.0 °C and it further decreased at intermediate layers. The simulated sea surface height and surface currents is validated with Aviso altimetry data. On the large scales the surface currents generated by model captures general structures of surface circulation. The monthly mean mixed layer depth (MLD) climatology computed from model is validated with observed monthly MLD climatology and found that the winter MLD is overestimated by model. In second experiment, model is forced with six hourly air-sea interaction fluxes from ERA-Interim and interannual simulations are obtained for the period 1998-2007. The monthly mean SST climatology obtained from above interannual simulation follows climatological annual cycle with cold biases in summer season. The weak SSTs (bias of the order of 1.0 to 1.5 °C) are observed in the summer for the period 2002-2007 in the model simulations. The monthly mean SST anomalies are well simulated by model except for the year 2006. The time evolution of monthly mean SST anomalies area averaged over different sub-basins are exhibits interannual variability. The comparison with satellite derived SSTs reveals that our model is able to capture both, the seasonal and inter-annual variability, although it still has a bias of the order of 1 to 1.2 °C. The model is able to reproduce the temperature at subsurface layer having the signatures of existence of intermediate water masses. The monthly mean mixed layer climatology derived from interannual simulations is quite well reproduced by model. In the Gulf of Lions, MLD values are reached upto 1500 meter deep in winter whereas it shows 50 meter in summer season. The time evolution of monthly mean mixed layer climatology derived from the model is able to reproduce annual variability. The interannual variability of monthly mean mixed layer depth is simulated quite well by model for the year 2004-2007. The timeseries of climatological, monthly and daily mixed layer depth which is area averaged over various sub-basins follows seasonal cycle. The high resolution regional model application developed in the current study is thus able to reproduce certain fields. The surface currents and eddy kinetic energy in the model shows small scale structures and strong variability. The model is also capable to generate mesoscale eddies in the western Mediterranean although model overestimated surface fields.
La investigación de la variabilidad climática en diferentes escalas de tiempo, como diario, mensual, estacional e interanual tiene suma importancia para la gestión de los procesos socio-económica en la región a escala global. De hecho, la variación en el clima tiene un impacto crucial en la agricultura, el agua, la salud, el turismo, la economía y el transporte. Por lo tanto el desarrollo de herramientas de predicción del clima es necesario que ayuda a gestionar estos sectores de manera más eficiente. Sin embargo, existen limitaciones en la producción de pronóstico climático precisa durante más de dos semanas de antelación debido a la naturaleza caótica del sistema climático, especialmente para la región como el Mediterráneo, que se caracteriza por una alta variabilidad interanual. Debido a su importancia y naturaleza desafiante, se está haciendo un esfuerzo colectivo para mejorar la habilidad de los modelos y la predicción del clima en el Mediterráneo. La contribución de esta tesis es un esfuerzo global, que consiste en el desarrollo de una aplicación de modelo de alta resolución en el Mediterráneo, que puede proporcionar una estimación fiable de la temperatura superficial del mar (TSM) y la profundidad de la capa mixta (MLD). Este enfoque se basa en el hecho de que la previsibilidad atmosférica en estacional a interanual escala de tiempo es significativamente dependiente de variación lenta condiciones límite inferior (por ejemplo, Charney y Shukla 1.981), es decir TSM mediterráneos. La resolución espacial de modelo se incrementa por tomar en cuenta los procesos de mesoescala en el Mediterráneo. Desde la primera radio interno de deformación de Rossby en el mar Mediterráneo es del orden de 10-15 kms, la resolución espacial de un remolino resolución de modelo debe tener al menos una resolución de la mitad del radio de Rossby. Basándose en esta suposición, la resolución espacial se explora a la orden de — 5 km (1/16°). El sistema de modelado regional de los océanos (ROMS), aprobada por la Universidad de Rutgers se utiliza en el estudio actual. El objetivo es validar ciertos campos (como SST y MLD) obtenidos a partir de simulaciones de modelos y estudiar las interacciones aire-mar. La validación se realiza mediante la realización de simulaciones de dos experimentos saber, climatológicos e interanuales. Los resultados del modelo simulado se validan con las observaciones, así como intercomparados para evaluar la habilidad del modelo. La media mensual climatología SST se obtiene a partir de diez años de ejecución del modelo forzada con climatológicas flujos aire-mar es bien capturados por la configuración del modelo y sigue el ciclo anual. Simulado Modelo SST climatología verano muestra sesgos del orden de 0,8 a 1,0 °C con observación (MEDATLAS) y 1,0-1,2 °C con otros conjuntos de datos (de intercomparación). La estructura vertical de la climatología de temperatura se encuentra para ser bien simulado por modelo en el que la capa superior muestra una diferencia de 1,0 °C y disminuyó aún más en las capas intermedias. Las corrientes simulados altura y la superficie de la superficie del mar se valida con los datos de altimetría aviso. En las grandes escalas de las corrientes superficiales generadas por el modelo capta las estructuras generales de la circulación superficial. La climatología media mensual profundidad de la capa mixta (MLD) calculada a partir del modelo se valida con la observada climatología mensual MLD y encontró que el invierno MLD se sobreestima el modelo. En segundo experimento, el modelo se ve obligado a seis por hora aire-mar flujos de interacción a partir de simulaciones ERA-Interim e interanuales se obtienen para el período 1998-2007. La climatología TSM mensual media obtenida desde arriba simulación interanual sigue el ciclo anual climatológica con sesgos fríos en la temporada de verano. Los TSM débiles (sesgo del orden de 1,0 a 1,5 °C) se observan en el verano para el período 2002-2007 en las simulaciones del modelo. Las anomalías medias mensuales de la TSM son bien simuladas por el modelo, excepto para el año 2006. La evolución en el tiempo de media área de anomalías de TSM mensual promedio durante diferentes subcuencas son exposiciones variabilidad interanual. La comparación con TSM satélite derivada revela que nuestro modelo es capaz de capturar tanto, la variabilidad estacional e interanual, a pesar de que todavía tiene un sesgo del orden de 1 a 1,2 °C. El modelo es capaz de reproducir la temperatura a la capa subsuperficial tener las firmas de la existencia de masas de agua intermedias. La media climatología capa de mezcla mensual derivado de simulaciones interanuales está bastante bien reproducido por modelo. En el Golfo de León, los valores de MLD se alcanzan hasta 1.500 metros de profundidad en invierno mientras que muestra 50 metros en temporada de verano. La evolución en el tiempo de la media climatología capa de mezcla mensual derivada del modelo es capaz de reproducir la variabilidad anual. La variabilidad interanual de media profundidad de la capa mixta mensual se simula bastante bien por el modelo para el año 2004-2007. Las series de tiempo de profundidad de la capa mixta climatológica, mensual y diaria, que es el área de media sobre varias subcuencas del siguiente ciclo estacional. La aplicación modelo regional de alta resolución desarrollado en el presente estudio es, pues, capaz de reproducir ciertos campos. Las corrientes superficiales y la energía cinética de Foucault en el modelo muestra las estructuras de pequeña escala y fuerte variabilidad. El modelo también es capaz de generar remolinos de mesoescala en el Mediterráneo occidental, aunque el modelo sobreestima campos superficiales.

Large-scale atmospheric disturbances play important roles in determining the general circulation of the atmosphere during the North Pacific boreal winter. A number of scientific questions have been raised due to these disturbances’ spatial and temporal complexity as well as the hydrological implication associated with them. In this dissertation, the principal goal is to further improve our understanding of the atmospheric high frequency (HF) and intermediate frequency (IF) disturbances active over the North Pacific. The study focuses on their energetics, intraseasonal and interannual variability, and the resulting hydrological impact over the eastern North Pacific and Western U.S. including extreme events. To delineate the characteristics of HF and IF disturbances in the troposphere, we first derive a new set of equations governing the local eddy kinetic energy (EKE), and assess the critical processes maintaining local budgets of the HF and IF EKE. The diagnosis assesses the 3-D patterns of energy flux convergence (EFC), barotropic conversion (BT), baroclinic conversion (BC), and cross-frequency eddy-eddy interaction (CFEI). The local EKE budget analysis is followed by an investigation of the modulation of HF and IF eddy activity by different modes of low frequency climate variability. On interannual timescales, the response of various local energetic processes to El Niño-Southern Oscillation (ENSO) determines the HF and IF EKE anomalies and the role of CFEI process is important in producing these anomalies. Also on interannual timescales, winter precipitation deficits associated with suppressed cyclonic activity, i.e., negative HF EKE anomalies, are linked to severe droughts over the U.S. Southern Great Plain (SGP) region. The suppressed cyclonic activity is, in turn, tied to phase changes in the West Pacific (WP) teleconnection pattern. On intraseasonal timescales, variations in HF disturbances (a.k.a. storm tracks) over the North Pacific are closely coupled with tropical convection anomalies induced by the Madden-Julian Oscillation (MJO), and partly drive larger scale intraseasonal flow anomalies in this region through eddy-eddy interactions. Anomalous HF eddy activity induces subseasonal transitions between “wet” and “dry” regimes over the west coast of North America. Also on intraseasonal timescales, the East Asian cold surge (EACS) is found to provide a remote forcing of the winter precipitation anomalies in the western U.S. This modulation is achieved through “atmospheric rivers” (ARs), which are narrow channels of concentrated moisture transport in the atmosphere and are responsible for over 70% of the extreme precipitation events in the western U.S.. EACS effectively modulates the IF disturbance activity over the North Pacific, and the anomalous IF disturbances lead to the formation of an AR over the eastern North Pacific that ultimately induces precipitation anomalies in the western U.S. Analyses of the simulations from the NCAR Community Climate System Model version 4 (CCSM4) demonstrate that the connections among the EACS, AR and western U.S. precipitation are better captured by a model with higher spatial resolutions. The improved simulation of these connections is achieved mainly through a better representation of the IF disturbances, and the associated scale-interaction processes in the higher resolution model.

Thesis (Ph.D.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2009.
Committee Chair: Peter J. Webster; Committee Member: Robert X. Black; Committee Member: John A. Knox; Committee Member: Judith A. Curry; Committee Member: Yi Deng.

Ce travail porte sur la quantification d'incertitude dans la modélisation des émissions de polluants atmosphériques dues au trafic routier d'une aire urbaine. Une chaîne de modélisations des émissions de polluants atmosphériques est construite, en couplant un modèle d’affectation dynamique du trafic (ADT) avec un modèle de facteurs d’émission. Cette chaîne est appliquée à l’agglomération de Clermont-Ferrand (France) à la résolution de la rue. Un métamodèle de l’ADT est construit pour réduire le temps d’évaluation du modèle. Une analyse de sensibilité globale est ensuite effectuée sur cette chaîne, afin d’identifier les entrées les plus influentes sur les sorties. Enfin, pour la quantification d’incertitude, deux ensembles sont construits avec l’approche de Monte Carlo, l’un pour l’ADT et l’autre pour les émissions. L’ensemble d’ADT est évalué et amélioré grâce à la comparaison avec les débits du trafic observés, afin de mieux échantillonner les incertitudes
This work focuses on the uncertainty quantification in the modeling of road traffic emissions in a metropolitan area. The first step is to estimate the time-dependent traffic flow at street-resolution for a full agglomeration area, using a dynamic traffic assignment (DTA) model. Then, a metamodel is built for the DTA model set up for the agglomeration, in order to reduce the computational cost of the DTA simulation. Then the road traffic emissions of atmospheric pollutants are estimated at street resolution, based on a modeling chain that couples the DTA metamodel with an emission factor model. This modeling chain is then used to conduct a global sensitivity analysis to identify the most influential inputs in computed traffic flows, speeds and emissions. At last, the uncertainty quantification is carried out based on ensemble simulations using Monte Carlo approach. The ensemble is evaluated with observations in order to check and optimize its reliability

The atmospheric response to the oceanic forcing in the eastern Pacific along the northern equatorial sea surface temperature (SST) front is investigated in terms of sensible and latent heat flux during the 6-month period 28 July 1999 through 27 January 2000. Of particular interest is the atmospheric boundary layer (ABL) response to oceanic Tropical Instability Waves (TIWs) that distort the SST front during May through January in normal years. In previous studies, time series of boundary layer properties clearly show the influence of TIWs but the relationship to spatial patterns of SST and wind stress has been inferred only from sparse in situ data. In this study, satellite observations are used to composite in situ data from moorings to compensate for the lack of a spatially dense mooring array. The variability in the position of the SST front caused by propagating TIWs enables fixed mooring locations to measure the atmospheric boundary layer (ABL) response from a large range of locations relative to the front. The satellite data enable determination of the precise location of the mooring relative to the front. The advantage of this strategy is the recurring measurement of the ABL response to the SST front over the six month period considered here. The results indicate that the TIW-induced perturbations of sensible and latent heat flux are spatially shifted in phase towards the east relative to the perturbations of SST. The maximum fluxes are not centered directly over the warmest water, but are shifted towards the portion of the frontal region where a disequilibrium boundary layer is expected due to the advection of colder air from the equatorial region. The changes of sensible and latent heat fluxes across the SST front have magnitudes of about 11 Wm⁻² and 126 Wm⁻², respectively. The sensible and latent heat flux patterns are interpreted in two complementary ways: (1) as an atmospheric response to the change of oceanic forcing as air flows across the SST front; and (2) as the atmospheric response to westward propagating TIWs along the SST front.
Graduation date: 2001

The relationship between the outgoing long-wave radiation (OLR) field over the tropical Pacific and wintertime monthly precipitation for the western U. S. is investigated, using the mid-latitude upper-air circulation as an intermediary. Principal components (PC's) of the 500mb monthly averaged height field over the NE Pacific and western North America are compared with those of the monthly tropical Pacific OLR field. It is found that, of the first 6 PC's of the height field, five are correlated significantly with the first 3 OLR field PC's at lags of between two and six months. Canonical correlations between the two sets of PC's are greatest at a lag of four months and are highly significant. When stratified by different levels of the OLR field PC's, the separations between means of the height field PC's are highly significant as well. Differing distributions of the height field PC ensemble are also found to be associated with different OLR field PC levels. The relationship between the 500mb height field and concurrent western district precipitation is examined. Using a hybrid model including both linear statistical and non-linear physical components it is found that considerably more of the variance in the precipitation can be explained by that of the height field alone than when the precipitation is inferred directly from a linear statistical model. A set of reconstructed height field PC's is predicted from OLR values based on the height field/OLR stratification associations compiled for a period separate from that of the forecast. Applied to the precipitation model, this results in predicted western district precipitation which is better correlated with the observations than is the equivalent precipitation forecast from the linear statistical relationship of precipitation to the Southern Oscillation Index.
Graduation date: 1995

Long-duration records are necessary to understand and assess the long-term dynamics of natural systems. The purpose of this research was to use dendrochronologic modelling to construct proxy histories of hydroclimatic conditions and Pacific salmon abundance in west central British Columbia. A multi-species regional network of tree ring-width and ring-density measurements was established from new and archived tree-ring chronologies. These chronologies were then used in multivariate linear regression models to construct proxy records of nival river discharge, summer temperature, end-of-winter snow-water equivalent (SWE), the winter Pacific North America pattern (PNA) and Pacific salmon abundance. All proxy hydroclimate records provide information back to 1660 AD. Reconstructions of July-August mean runoff for the Skeena and Atnarko rivers describe below average conditions during the early- to mid-1700s and parts of the early-, mid- and late-1900s. Models describe intervals of above average river discharge during the late-1600s, the early-1700s and 1800s, and parts of the early- and mid-1900s. Fluctuations in proxy reconstructions of July-August mean temperature for Wistaria and Tatlayoko Lake, May 1 SWE at Mount Cronin and Tatlayoko Lake and October-February PNA occurred in near synchrony with the shifts described in runoff records. Episodes of above average runoff were typically associated with periods of enhanced end-of-winter SWE, below average summer temperature and positive winter PNA. A history of Pacific salmon abundance was reconstructed for four species of salmon (chinook, sockeye, chum and pink) that migrate to coastal watersheds of west central British Columbia. Proxy records vary in length and extend from 1400 AD, 1536 AD and 1638 AD to present. Salmon abundance reconstructions varied throughout the past six centuries and described significant collapse in population levels during the early-1400s, the late-1500s, the mid-1600s, the early-1700s, the early-1800s and parts of the 1900s. Wavelet analyses of reconstructed hydroclimate and salmon population records revealed low- and high-frequency cycles in the data. Correlation analyses related reconstructions to atmospheric teleconnection indices describing variability in North Pacific sea surface temperatures and the Aleutian Low pressure centre. To a lesser degree, relationships were also established between reconstructions and the El Niño-Southern Oscillation. Results thus confirm the long-term influence of large-scale ocean and atmospheric circulation patterns on hydroclimate and Pacific salmon abundance in west central British Columbia. The reconstructions introduced in this thesis provide insights about the long-term dynamics of the west central British Columbia environment. Several reconstructions presented in this thesis provide novel contributions to dendrohydroclimatic and paleoecologic research in Pacific North America. Proxy runoff records for the Skeena and Atnarko rivers are the first to be constructed for nival-regime basins in British Columbia. The models of Skeena River runoff and Mount Cronin SWE are additionally the first reconstructions of runoff and snowpack in Pacific North America based on a ring-density chronology, demonstrating the significant contribution that wood density measurements can make to dendrohydroclimate research. The models of Pacific salmon stocks are the first to utilize climate-sensitive tree-ring records to construct a history of regional salmon abundance and thus represent a significant advancement to paleoecological modelling.
Graduate