A key determinant of atmospheric circulation patterns and regional climatic conditions is sea surface temperature (SST). This has been the motivation for the development of various teleconnection methods aiming to forecast hydro-climatic variables. Among such methods are linear projections based on teleconnection gross indices (such as the ENSO, IOD, and NAO) or leading empirical orthogonal functions (EOFs). However, these methods deteriorate drastically if the predefined indices or EOFs cannot account for climatic variability in the region of interest. This study introduces a new hydro-climatic forecasting method that identifies SST predictors in the form of dipole structures. An SST dipole that mimics major teleconnection patterns is defined as a function of average SST anomalies over two oceanic areas of appropriate sizes and geographic locations. The screening process of SST-dipole predictors is based on an optimization algorithm that sifts through all possible dipole configurations (with progressively refined data resolutions) and identifies dipoles with the strongest teleconnection to the external hydro-climatic series. The strength of the teleconnection is measured by the Gerrity Skill Score. The significant dipoles are cross-validated and used to generate ensemble hydro-climatic forecasts. The dipole teleconnection method is applied to the forecasting of seasonal precipitation over the southeastern US and East Africa, and the forecasting of streamflow-related variables in the Yangtze and Congo Rivers. These studies show that the new method is indeed able to identify dipoles related to well-known patterns (e.g., ENSO and IOD) as well as to quantify more prominent predictor-predictand relationships at different lead times. Furthermore, the dipole method compares favorably with existing statistical forecasting schemes. An operational forecasting framework to support better water resources management through coupling with detailed hydrologic and water resources models is also demonstrated.

The atmospheric drivers of winter and summer surface climate in western Canada are evaluated using a synoptic climatological approach. Winter snow accumulation provides the largest contribution to annual streamflow of the north-flowing Mackenzie and east-flowing Saskatchewan Rivers, while summer water availability is primarily a product of basin-wide precipitation and evapotranspiration. A catalogue of dominant synoptic types is produced for winter (Nov-Apr) and summer (May-Oct) using the method of Self-Organizing Maps. Water availability, quantified through high-resolution gridded temperature and precipitation data, associated with these synoptic types is then determined. The frequency of dominant types during positive/negative phases of the Southern Oscillation Index, Pacific Decadal Oscillation, and Arctic Oscillation reveal the atmospheric processes through which these teleconnections influence surface climate. Results from the winter analysis are more coherent than summer, with strong relationships found between synoptic types, teleconnections, and surface climate. Although not as strong, links between summer synoptic types and water availability also exist. Additionally, time-series analysis of synoptic type frequencies indicates a trend toward circulation patterns that produce warmer, drier winters as well as an earlier onset and extension of the summer season. This study increases our understanding of the atmospheric processes controlling the distribution of water resources in western Canada. / Graduate / 0388 / 0725 / 0368 / bwnewton@uvic.ca

The connection between Upper Tropospheric Cyclonic Vortex (UTCV) and Brazilian Northeast Jet Stream (BNEJS) was analyzed for 9 years between 1988 and 2000, separated by El Niño, La Niña and Neutral years. Through the reanalysis products from NCEP, and METEOSAT satellite images in the infrared channel, were observed 167 UTCVs, most of them originated over the Atlantic Ocean with an average last of 4 days and showed no significant variability in years of El Niño and La Niña. Approximately 54% of the observed UTCVs were associated to air currents superior than 20m.s-1 in its periphery, these currents are called BNEJS. In El Niño years was observed an increase of BNEJS cases associated to UTCV, while in La Niña years, the number of occurrences was practically the same as in neutral years. The BNEJS showed intensitity up to 40 m.s-1, and the most observed wind directions were from south, southeast, northwest and west. Thus, 3 patterns of occurrence of BNEJS were identified, named Meridional, Zonal and Transversal. The Meridional BNEJS occurs in the UTCVs west periphery, usually over the continent, showing the upward movements between the BNEJS and the Northern Subtropical Jet Stream (NSJS). And finally, the transversal BNEJS, showed two kinds of currents, one from southeast and another from northwest. In these cases, the UTCVs axis showed an inclination to west and the upward movements were observed in the UTCVs periphery, where the winds were weaker. Thus, three cases were chosen to represent the observed patterns and investigate the vertical movements, comparing to the cloudiness in the satellite images, where was observed, in both cases, that the upward movements doesn t exists or are too weak in the jet streak BNEJS area. / Conselho Nacional de Desenvolvimento Científico e Tecnológico / A ligação entre Vórtice Ciclônico em Altos Níveis (VCAN) e a Corrente de Jato do Nordeste Brasileiro (CJNEB), foi analisada durante 9 anos entre 1988-2000, divididos em períodos de El Niño, La Niña e Neutro. Através dos produtos de reanálise do NCEP, e imagens do satélite METEOSAT no canal infravermelho, foram observados 167 VCAN s, em grande maioria originados sobre o oceano Atlântico, com uma duração média de 4 dias, não apresentando variabilidade significativa em anos de El Niño e La Niña. Dos VCAN s observados, aproximadamente 54%, estavam associados a correntes de ar superiores a 20m.s-1 em sua periferia, essas correntes são chamadas de CJNEB. Em anos de El Niño, foi observado um aumento dos casos de CJNEB associados à VCAN, enquanto que em anos de La Niña, o número de ocorrências foi praticamente o mesmo que em anos neutros. As CJNEB apresentaram intensidade de até 40 m.s-1, e as direções mais observadas foram de sul, sudeste, noroeste e oeste. Assim, foram identificados 3 padrões de ocorrência de CJNEB, denominadas de Meridional, Zonal e Transversal. A CJNEB Meridional ocorre na periferia oeste do VCAN, geralmente sobre o continente, apresentando os movimentos ascendentes no lado oeste da corrente. A CJNEB Zonal ocorreu sobre a periferia norte do VCAN, apresentando movimentos ascendentes entre a CJNEB e o Jato Subtropical do Hemisfério Norte (JSTHN). E finalmente, a CJNEB Transversal, que apresentou dois tipos de correntes, uma de sudeste e outra de noroeste. Nesses casos, o eixo do VCAN apresentou uma inclinação para oeste, e os movimentos ascendentes foram observados na periferia do VCAN, onde os ventos foram mais fracos. Assim, três casos foram escolhidos a fim de representar os padrões observados e investigar os movimentos verticais, comparando com a nebulosidade nas imagens de satélites, onde foi observado em ambos os casos, que os movimentos ascendentes inexistem ou são muito fracos na região mais intensa da CJNEB ( Jet Streak ).

Este estudo discute uma climatologia de 59 anos (1949-2007) de bloqueios no Hemisfério Sul (SH) usando dados de altura geopotencial em 500-hPa das reanálises do National Center for Environmental Prediction / National Center for Atmospheric Research (NCEP-NCAR). A variabilidade espaço-temporal dos eventos de bloqueio e associações com o El Niño/Oscilação do Sul (ENOS) também foram examinadas. Adicionalmente, os bloqueios foram investigados em dois Modelos de Circulação Geral Acoplados Atmosfera-Oceano de clima (MCGAO) do Intergovernamental Painel for Climate Change (IPCC), o ECHAM5/MPI-OM e o MIROC 3.2. Dois cenários simulados foram analisados: O clima do século XX e o cenário de emissão A1B. Os episódios do ENOS foram identificados usando dois métodos. O primeiro foi o Índice Oceânico Mensal do Niño (ONI) do Climate Prediction Center (CPC-NCEP). O segundo método foi baseado em Funções Empíricas Ortogonais (EOF) e foi aplicado nos MCGAOs. Similarmente, também foi examinado a influencia combinada do ENOS e a Oscilação Antártica (AAO) na ocorrência e características dos bloqueios. O índice diário da AAO foi obtido pelo CPC-NCEP. Os índices convencionais de bloqueios detectam principalmente variações longitudinais. Este trabalho propõe um índice de bloqueio que detecta, além de variações longitudinais também as variações latitudinais dos bloqueios. Cinco setores relevantes de bloqueios foram examinados em detalhes: Indico Sudoeste (SB1), Pacífico Sudoeste (SB2), Pacífico Central (SB3), Pacífico Sudeste (SB4) e Atlântico Sudoeste (SB5). Além disso, foram investigados duas grandes regiões do Pacífico Sul: Pacífico Oeste e Pacífico Leste. Foi encontrado que a escala média típica dos eventos de bloqueio varia entre 1,5 e 2,5 dias. Além disso, a duração dos eventos depende da latitude, com eventos de maior duração observados em latitudes mais altas. Diferenças longitudinais estatisticamente significativas na freqüência do escoamento bloqueado foram observadas entre as fases Quente e Neutra do ENOS desde o outono a primavera. Episódios intensos da fase Quente do ENOS (isto é, moderados a fortes) tendem a modificar o local preferencial de bloqueio, mas não a freqüência. Por outro lado, os episódios fracos da fase Quente do ENOS estiveram associados relativamente com alta freqüência. Os Eventos de bloqueio durante o ENOS+ duram, em média, mais um dia relativamente aos episódios Neutros. Em contraste, a fase Fria do ENOS (ENOS-) caracterizou-se pela redução dos eventos de bloqueio sobre o setor do Pacífico Central, exceto durante os meses do verão austral. Entretanto, nenhuma diferença estatisticamente significativa foi detectada na duração dos eventos. Composições de anomalias de vento em 200-hPa indicam que o enfraquecimento (fortalecimento) do jato polar em torno de 60ºS durante a AAO negativa (positiva) em ambas as fases do ENOS tem uma importância significativa no aumento (redução) dos eventos de bloqueio. Um significativo aumento estatístico dos eventos sobre o setor do Pacífico Sudeste foi observado durante a AAO negativa em ambas as fases do ENOS. Ainda, um aumento (redução) dos eventos foi observado sobre a região do Pacífico Oeste na fase negativa (positiva) da AAO durante o ENOS-. Em contraste, durante o ENOS+ não houve diferenças estatisticamente significativas na distribuição longitudinal dos eventos separado de acordo com as fases opostas da AAO, embora haja um aumento (redução) dos eventos da região do Pacífico Oeste para o Pacífico Leste durante a fase negativa (positiva) da AAO. Os MCGAOs simularam corretamente a amplitude do ciclo anual observado. Também, ambos os MCGAOs simularam melhor a duração e o local preferencial do que freqüência. Nenhum MCGAO simulou adequadamente a freqüência durante a fase Neutra do ENOS. O ECHAM5/MPI-OM (rodada 2) mostra um erro sistemático que levam a uma superestimativa na freqüência de eventos sobre o Pacífico Leste durante as fases Neutra e Fria do ENOS. As diferenças entre as duas versões do MIROC 3.2 indicam que a alta resolução nos modelos melhora o desempenho em simular a freqüência de bloqueios. / This study discusses 59-yr climatology (1949-2007) of Southern Hemisphere (SH) blockings using daily 500-hPa geopotential height data from National Center for Environmental Prediction / National Center for Atmospheric Research (NCEP-NCAR reanalysis. The spatiotemporal variability of blocking events and associations with El Nino/Southern Oscillation (ENSO) are examined. Additionally, blockings were examined in two Intergovernmental Panel for Climate Change (IPCC) Coupled General Circulation Models (CGCM), ECHAM5/MPI-OM and MIROC 3.2. Two sets of simulations were examined: the climate of the 20th century and the A1B emission scenario. ENSO episodes were identified using two methods. The first method was the Monthly Oceanic Niño Index (ONI) from the Climate Prediction Center (CPC-NCEP). The second method was based on Empirical Orthogonal Function (EOF) and was applied to identify ENSO episodes in the CGCMs. Similarly, the combined influence of ENSO and the Antarctic Oscillation (AAO) on the occurrence and characteristics of blockings was also examined. The daily AAO index was obtained from CPC/NCEP. Most conventional blocking indices detect longitudinal variations of blockings. In this study we propose a new blocking index that detects longitudinal and latitudinal variations of blockings. The following relevant sectors of blocking occurrence were identified and examined in detail: Southeast Indian (SB1), Southwest Pacific (SB2), Central Pacific (SB3), Southeast Pacific (SB4) and Southwest Atlantic (SB5) oceans. In addition, we investigated two large regions of South Pacific: West Pacific and East Pacific. We found that the typical timescale of a blocking event is about ~1.5 2.5 days. Nonetheless, the duration of events depends on the latitude, with larger durations observed at higher latitudes. Statistically significant differences in the longitude of blockings are observed between Warm (ENSO+) and Neutral ENSO phases from the Austral fall to spring. Moderate to strong Warm ENSO episodes modulate the preferred locations of blockings but do not play a significant role for variations in their frequency. On the other hand, weak ENOS+ episodes were associated with relatively high frequency of blockings. Blocking events during ENSO+ last on average one more day compared to events that occur during Neutral episodes. In contrast, Cold (ENOS-) ENSO episodes are characterized by a decrease of blockings over the Central Pacific sector, except during the Austral summer months. However, no statistically significant differences are detected in the duration. Composites of 200-hPa zonal wind anomalies indicate that the weakening (strengthening) of the polar jet around 60oS during negative (positive) AAO phases in both ENSO phases plays a major role for the relative increase (decrease) of blocking events. A statistically significant increase of events over Southeast Pacific is observed during negative AAO phases in both ENSO phases. Moreover, an increase (decrease) of events is observed over West Pacific region when negative (positive) AAO phases occur during ENSO-. In contrast, during ENSO+ there is no statistically significant difference in the longitudinal distribution of events separated according to opposite AAO phases, although there is an increase (decrease) in the events from West Pacific region to East Pacific during negative (positive) AAO phase. The CGCMs investigated in this study correctly simulated the amplitude of observed annual cycle of geopotential height in the extratropics. Also, both CGCMs show a better performance in simulating the duration and preferred locations of blockings than their frequency. None of these CGCMs simulated well the frequency during Neutral ENSO phase. The ECHAM5/MPI-OM (run2) shows systematic biases in some regions. For instance, this model overestimates the frequency of blockings over East Pacific region during Cold and Neutral ENSO phases. The differences between the two versions of MIROC 3.2 indicate that the increase in resolution improves the performance of the model in simulating the frequency of blockings.

M.Phil. (Energy Studies) / Southern Africa is a major source of regional aerosols and trace gases from biomass burning, and this creates a need for experimental validation and systematics of the magnitude and frequency of aerosol transport episodes affecting the atmosphere of the region. This study links surface measurements of biomass burning atmospheric aerosols and trace gases with air mass trajectory analysis to determine transport pathways for periods of high and low concentrations. The hypothesis of this study is that from chemical signatures of trace gases and aerosols, as well as trajectory analyses, it is possible to identify sources of these emissions from industrial, traffic, marine and biomass burning activities. Consequently, frequencies, durations, intensities and seasonal variations of trace gases can be established. The study aims to interpret the long-term atmospheric monitoring record from a remote monitoring station at Botsalano (North West Province, South Africa) to determine the origin, frequencies, durations, intensities and seasonal occurrences of aerosol/haze episodes influencing the atmosphere of southern Africa. A suite of trace gas analysers and a Differential Mobility Particle Sizer (DMPS®) were used to measure ground level trace gas and aerosol quantities. MATLAB® scripts were used in performing quality assurance and processing to provide a working set of data from which different fire periods could be selected. Fire signatures, based on excess CO above average tropospheric levels and episodes of enhanced particulate matter concentrations in the 10 to 200 nm range, were identified using MATLAB® scripts and Excel®. Altogether 36 plumes were accepted as biomass burning plumes. Twenty-nine fire plumes had weak signals with excess CO ratios ranging between 0.07 and 0.32; seven plumes had strong signals ranging between 0.41 and 0.64. The occurrence of identified biomass burning plumes was high in the dry season from May to October (83%) and low (17%) during the wet season from November to April. Four pathways were identified for the long-range transportation of biomass burning aerosols to the site: easterly, south-westerly, re-circulation and northerly modes, with occurrence frequencies of 39%, 31%, 22% and 8%, respectively. Anti-cyclonic circulation was observed over southern Africa and was evident in the re-circulation and Indian Ocean slow modes. CO and Aitken-mode aerosol number intensities were generally larger for fire emissions arriving in the easterly and south-westerly air masses when compared with those arriving in re-circulation and northerly air masses. Easterly and south-westerly flows were dominated by Aitken-mode aerosol, whereas accumulation mode particles dominated in the re-circulation and northerly modes. Consequently, easterly and south-westerly flows transported emissions from young/fresh fire plumes, with source regions probably close to Botsalano. Re-circulation and northerly flows were responsible for transport of rather aged plumes from more distant regional fires. Based on forward trajectories, this study revealed that the 2006/2007 measurement period exhibited transport features of a La Niña ENSO during which transport of biomass v burning aerosols towards the south in the Indian Ocean slow and Indian Ocean fast modes was most frequent. This study is significant in that it complements earlier studies of regional aerosol transport over the sub-continent and adds to the understanding of the regional scale generation and transport of trace substances through the atmosphere. Furthermore, the study combines a technique for identifying enhanced CO concentrations as a unique identifier of large scale biomass combustion events with the use of the Aitken-mode particle number densities and size distributions. This technique reveals aspects of aerosol growth dynamics through the changing size distributions, thereby adding fresh insights normally not available through conventional particle volume/mass concentrations measurements.

The effects of a non-zero background state on atmospheric dynamics is explored through simple models and observations. Firstly, we examine the effects of moisture gradients on the stability and propagation of Rossby waves in a mid-latitude -plane. We begin by a consistent derivation of the forced quasi-geostrophic equations on a -plane to understand the constraints placed by geostrophy on the time scale of condensation. We see that the presence of meridional gradients of moisture results in a slowdown of the waves. On the introduction of zonal gradients of moisture, the waves become unstable, and for certain parameters which are representative of the real atmosphere, they propagate eastward and mature on an intra-seasonal timescale. The mechanism of the in hence of moisture on waves is understood by thinking of condensation as providing an \equivalent" potential vorticity (PV) gradient which opposes the dynamical PV gradient. Secondly, we look at the effects of a mean background ow on the Matsuno-Gill response in the spherical shallow water system. The mean ow is prescribed to resemble the climatological upper tropospheric zonal wind structure in the atmosphere. As the strength of the ow increases, the equatorially trapped Matsuno-Gill response rst transforms into a poleward propagating Rossby wavetrain. As the strength of the mean ow reaches values similar to that observed in the atmosphere, the stationary wave response becomes a zonally oriented quadrupole structure. This structure bears a striking resemblance to the observed upper level structure of the Madden-Julian oscillation (MJO). The time evolution of this quadrupole structure is quick enough to be relevant on MJO timescales, and the structure is quite robust across a range of values for the drag coefficient. Finally, we look at the role played by low frequency variability in the Pacific in the recent expansion of the Hadley cell. We find that the dominant effect of the low frequency variability is a stationary dispersive Rossby wavetrain extending from the tropical Paci. We further find that most of the observed expansion of the Hadley cell can be accounted for by this low frequency variability. We nd that large scale changes such as the changes in the equator-pole temperature gradient or midlatitude static stability need not be invoked to understand the observed expansion.

MENVSC / Department of Geography and Geo-Information Sciences / The process of cloud formation and distribution in the atmospheric circulation system is very important yet not easy to comprehend and forecast. Clouds affect the climate system by controlling the amount of solar radiation, precipitation and other climatic variables. Parameterised induced General Circulation Model (GCMs) are unable to represent clouds and aerosol particles explicitly and their influence on the climate and are thought to be responsible for most of the uncertainty in climate predictions. Therefore, the aim of the study is to investigate the climate of South Africa as simulated by Super Parameterised Community Atmosphere Model (SPCAM) for the period of 1987-2016. Community Atmosphere Model (CAM) and SPCAM datasets used in the study were obtained from Colorado State University (CSU), whilst dynamic and thermodynamic fields were obtained from the NCEP reanalysis ll. The simulations were compared against rainfall and temperature observations obtained from the South African Weather Service (SAWS) database. The accuracy of the model output from CAM and SPCAM was tested in simulating rainfall and temperature at seasonal timescales using the Root Mean Square Error (RMSE). It was found that CAM overestimates rainfall over the interior of the subcontinent during December - February (DJF) season whilst SPCAM showed a high performance in depicting summer rainfall particularly in the central and eastern parts of South Africa. During June – August (JJA), both configurations (CAM and SPCAM) had a dry bias with simulating winter rainfall over the south Western Cape region in cases of little rainfall in the observations. CAM was also found to underestimate temperatures during DJF with SPCAM results closer to the reanalysis. The study further analyzed inter-annual variability of rainfall and temperature for different homogenous regions across the whole of South Africa using both configurations. It was found that SPCAM had a higher skill than CAM in simulating inter-annual variability of rainfall and temperature over the summer rainfall regions of South Africa for the period of 1987 to 2016. SPCAM also showed reasonable skill simulating (mean sea level pressure, geopotential height, omega etc) in contrast to the standard CAM for all seasons at the low and middle levels (850 hPa and 500 hPa). The study also focused on major El Niño Southern Oscillation (ENSO) events and found that SPCAM tended to compare better in general with the observations. Although both versions of the model still feature substantial biases in simulating South African climate variables (rainfall, temperature, etc), the magnitude of the biases are generally smaller in the super parameterized CAM than the default CAM, suggesting that the implementation of the super parameterization in CAM improves the model performance and therefore seasonal climate prediction. / NRF

No description available.

No description available.

No description available.